housing Archives - Nerd Corner

DIY keypad lock – 3D printing and code

Nerds — Tue, 17 Dec 2024 20:44:05 +0000

A cupboard that should always be locked and five people who need to access it – a classic challenge. The obvious solutions? Five keys in circulation or a single person who manages the key so that you have to borrow it every time. But we’ve all been there: the key ends up lying in the cupboard, under the carpet or behind the flower pot.

But wouldn’t it be much more practical to do away with physical keys altogether? Nowadays, there are numerous ways to open a lock: Fingerprint scanners, facial recognition, NFC, numeric codes, dials – or, of course, brute force methods such as explosives and brute force. But if you are looking for an inexpensive, non-violent and simple solution, the keypad lock comes into focus.

Surprisingly, there are hardly any really good DIY solutions for hobbyists on the Internet. So I tackle it myself – my first keypad lock, which I simply call “Version 1”.

This might also be interesting for you: Do it yourself powerbank with voltage regulator and voltmeter

Construction of the housing

The initial focus is on the housing and the keypad holder. The first question that always arises is: How big should it be? The answer depends on several factors:

Which components are required? Each component takes up space and influences the design.
How much space do the components take up? A compact design is advantageous, but must not restrict functionality.
What are the haptics and operability like? The keypad should be comfortable to use without being too cramped or impractical.

These considerations form the basis for the housing design – because good planning saves time and nerves later on.

What will be inside the housing?

The central component is, of course, the membrane keypad (1.0.1). It has the following dimensions:

Width: 69 mm
Length: 76 mm
Thickness: 0.6 mm (or 0.95 mm above the keys)

The keypad also has a ribbon cable with DuPont sockets for connection to a microcontroller. The cable itself is 85 mm long and 17.78 mm wide.

The control center of the lock is the Nano (1.0.2). To accommodate it neatly in the housing and to make the cable connections as convenient as possible, I opted for a Nano expansion board with screw terminals (1.0.4).

A hollow socket (5.5 x 2.1 mm, 1.0.4) is used for the emergency power supply so that the lock continues to function even in the event of a power failure.

The pin and socket connectors (1.1.1) serve as the central power distribution and are later soldered to the breadboard (1.1.2). Jumper cables (1.1.3) are used to ensure that all components are reliably connected. Depending on the position of the components, different lengths are required – in this case 10 cm and 20 cm.

For the status display of the keypad lock, I use Neo Pixel addressable LEDs of type WS2812b (1.2.1). These can be used to control different colors and effects to visually display the current status of the lock.

I will go into the positioning of the screws in more detail later.

Now that the components have been determined, I can think about the size of the housing. This is not only determined by the installed elements, but above all by the usability and feel.

We encounter keypads every day – on ATMs, telephones, door lock systems and, of course, smartphones. The decision for the depth of the housing is based on a positive memory of my penultimate workplace: the keypad lock at the entrance was raised and easily accessible from both sides. You could operate it comfortably with your right or left thumb, and the rounded corners provided a pleasant feel when you put your hand on it.

Keypad lock Housing design

This results in a depth of 45 mm (2.0.3). For better ergonomics, the corners have a radius of 15 mm (R15) and the surrounding upper edges have a radius of 10 mm (R10). I am aware that these roundings slightly reduce the interior space, but the comfort and appearance outweigh this disadvantage.

The width and height of the housing are determined by the components to be installed. The space for the cabling must also be taken into account. Particularly important: When installed, the Nano should still be accessible with a standard USB mini cable, for example to be able to install new programs.

Mounting and fastening

Four M3 threads (2.0.1) on the inside allow the support plate to be screwed on.
In addition, there are four mounting points with Ø4.2 mm holes for attaching the housing to a door, cover or wall.
The housing has a window (2.0.2) measuring 60 × 67 mm, which is intended for the keypad. This is later filled with the carrier plate.
Retaining columns with M2 threads and the opening for the hollow socket (1.0.4) are marked with orange ellipses (2.0.1, 2.0.3).
The next picture (2.0.4) shows the external dimensions: 110 mm wide and 117 mm high.
In addition, an aperture or slot 50 mm long is required for the LED cover (2.0.5).

For the wall thickness of the housing, I have provided 2 mm throughout – stable enough for the intended purpose.

With the housing construction completed, we can now continue with the other components.

The support plate – the central mounting element

The next important component is the carrier plate. The name is self-explanatory: With the exception of the hollow bushing, all components are attached here. This system offers several advantages over direct mounting in the housing:

Easy mounting outside the housing – More space and better handling when wiring.
Modularity – different carrier plates with different components are possible.
Simple enclosure design – The enclosure design remains simpler and more flexible.
Easy replacement – Components can be replaced or extended more easily.

But there is another decisive advantage for the keypad lock in particular:

The keypad is glued directly into a designated recess in the carrier plate (2.1.1). The carrier plate and keypad are then inserted into the housing from behind and fixed in place with M3 screws. The frame of the window in the housing completely covers the edge and the cables.

Safety aspect: The window is dimensioned in such a way that the edge and the cables remain concealed, but the buttons are fully visible and operable. This means that the keypad cannot be removed without destroying it – an important protective mechanism against tampering.

Fastening the components to the carrier plate

There are various mounting options for the electronics on the back (2.1.2) of the carrier plate:

M3 thread for the nano adapter (2.1.3) – As nano adapters on the Internet often have different hole spacings, there is an additional fastening thread on the right-hand side (2.1.2) for flexible adjustment. If the holes still do not fit exactly, they can be carefully widened – but without damaging the adapter’s conductor tracks.

M2 thread for the Nano R3 ATMEGA168P (2.1.4) – An alternative, cost-effective solution instead of a Nano R3 with adapter.

M2 thread for the breadboard (20×80 mm, 1.1.2, 2.1.5) – This is used for power distribution and connects all power supply lines neatly at a central point.

The LED cover and its attachment

The LED cover (2.2.1) has been designed so that it is clicked into the slot (2.0.5) of the housing from the rear. The radius on the outside of the LED cover corresponds to the housing radius, creating a smooth transition and allowing the cover to blend in seamlessly.

I don’t need to redesign the mounting bridge (front 2.2.2, back 2.2.3) as I have already used it successfully in other projects.

Mounting the LEDs

Now it remains to mount the three WS2812b LEDs (1.2.1). I will explain why exactly three LEDs are needed later in the programming section of this article.

The development of the LED holder (SMD50, 2.2.4) was more complex than expected. Of course, you could simply glue, clamp or hot glue the LED strips – but that seemed too unprofessional to me.

I therefore invested a lot of time and effort in designing a perfect holder. The result can be seen in picture 2.2.5.

Further information:

For details on the construction, there is a separate article on NerdCorner.

3D printing of the components

Once the design has been completed, the parts must now be printed.

Material selection for the individual components:

Housing (3.0.1): Printed with ABS filament, consisting of front and back.
Carrier plate (3.0.2): made from PLA filament.
LED cover (3.0.3): produced upright in the printer, printed with PLA+ in the color “natural”.
LED terminals (3.0.4): also made of PLA+, manufactured in the same process as the LED cover.
Bridge for the hollow socket: printed from PLA filament, analogous to the carrier plate.

With these materials, the mechanical and thermal properties of the components are optimally matched to their respective applications.

Post-processing of the components

After printing, both the printed parts and some purchased parts need to be processed.

1⃣ Cleaning the 3D printed parts

Removal of support material and protruding print residues.

2⃣ Cutting the thread
Housing (4.0.1):

Four M3 threads (Attention: blind holes! Proceed carefully when cutting so as not to push the base outwards).
Two M2 threads (4.0.2).
Support plate (4.0.3):
- The M2 threads marked in blue must be cut in any case.
- When using a nano adapter with screw terminals (2.1.4), the M2 threads marked in red must also be cut.

3⃣ Shortening the perforated grid plate

The perforated grid plate (4.0.4) must be shortened to 8 to a maximum of 10 perforated grids.
Important: The mounting holes should be retained (see 4.0.5).

4⃣ Shortening the pin header

Shorten the pin header to eight pins using a side cutter (4.0.6).

Soldering the components

Now it’s time to solder the parts. First we concentrate on the power supply board:

1⃣ Soldering the power supply board

Perforated grid plate (4.0.5): Soldering the base strip (1.1.1) and the pin strip (4.0.6).
Pin strip (4.1.2): A two-row pin and skirting board is soldered on. We connect the two rows on the back with solder.
The rows differ in male and female as well as in the colors: red for plus and black for minus. This makes it easier to connect the power supply.

2⃣ Soldering the WS2812B LEDs

Soldering the connections of the WS2812B LED strip (4.1.3).

3⃣ Soldering the hollow socket

Finally, the hollow socket (1.0.4) is soldered (4.1.4).
Detailed instructions on soldering the hollow socket can be found in a separate article. It is important to know the exact procedure in order to avoid mistakes.

Assembling the keypad lock

1⃣ Installing the LED cover

First click the LED cover (2.2.1) into the housing.
Glue the LED cover in the intended places as shown in pictures 5.0.1 and 5.0.2.

2⃣ Plug in the Nano R3

Insert the Nano R3 (1.0.2) into the Nano adapter (5.0.3) of your choice.

3⃣ Installing the Nano adapter

Screw the Nano adapter (1.0.3) with the inserted Nano R3 (1.0.2) to the back of the carrier plate (4.0.3).
Use the M3 threads on the carrier plate and the screws (1.2.2), as shown in pictures 5.0.4 and 5.0.5.

4⃣ Attaching the power supply

Attach the power supply (4.1.2) to the back of the carrier plate (4.0.3) using the screws (1.2.4).
See figure 5.0.6.

Mounting the keypad on the support plate

1⃣ Selecting the screw length

Make sure to select the correct screw length as shown in Figure 5.1.1.
Screws must not be too long, otherwise they will protrude from the adhesive surface when the keypad is attached and the keypad cannot be glued on cleanly.

2⃣ Preparing the keypad

Remove the protective film from the keypad (1.0.1).
To remove the film, use a carpet knife to carefully get between the adhesive layer and the protective film at one corner (see 5.1.2).
Once you have reached the corner, peel off the entire protective film (see 5.1.3).

3⃣ Stick on the keypad

Insert the keypad (1.0.1) into the recess on the front of the carrier plate (2.1.1) and press it firmly into place.
The keypad must be completely recessed and must not protrude over the edge (see 5.1.4).
Make sure that the cables are also in the recess (see 5.1.5).

Wiring the keypad to the Arduino Nano R3

1⃣ Using jumper cables

Jumper cables (10 cm long, male-male) are used to connect the keypad to the Arduino Nano R3 (see 5.2.1).

2⃣ Connecting the cables

Make sure that you do not twist the cables, but only bend them.
The left cable is connected to D2 of the Arduino and the right cable to D8.
There are seven cables in total, which occupy the connections D2 to D8 (see 5.2.3).

3⃣ Use pin headers

As the pitch of the Arduino adapter and the keypad do not match, you can use pin strips to make the connection.

4⃣ Fastening the LED terminals

The clips (3.0.4) for the WS2812B LEDs are clicked onto the LEDs.
It is best to do this on a flat surface (see 5.2.4).

5⃣ Attaching the LED strip

The WS2812B strip is now pushed onto the center of the top of the carrier plate (see 5.2.5 Front and 5.2.6 Rear).

Assembling the carrier plate and housing

1⃣ Screwing the support plate to the housing (5.3.1)

Make sure that you use M3 screws that are not too long. Otherwise, they could push a bump into the front of the housing when tightened.
The alignment of the carrier plate in the housing is important: the LED strip should be on the same side as the LED cover.
After screwing, the keypad should be lightly pressed against the inner frame of the housing (see 5.3.2 and 5.3.3).

2⃣ Pre-assembly of the hollow socket for the emergency power supply

For the emergency power supply, you must pre-assemble the hollow socket and screw it to the housing.
The hollow socket with bridge and nut is shown in Figure 5.3.4.
Insert the hollow bush into the round recess of the bridge.
Lock the hollow bushing with the nut on the other side of the bridge.

3⃣ Fastening the hollow bush in the housing

The hollow bush with the bridge is then screwed to the retaining pillars provided in the housing using M2 screws (see 5.3.5 and 5.3.6).

Connecting the cables and completing the power supply

1⃣ Connecting the control cable for the servo motor

The control cable for the servo motor is connected to pin D9 of the Nano R3 (5.4.1).

2⃣ Connecting the power supply for the Nano R3

The power supply for the Nano R3 is connected to the GND pin and the VIN pin of the Nano R3 (5.4.2).

3⃣ Connecting the control cable for the WS2812B

The control cable for the WS2812B LED strip is connected to pin D10 of the Nano R3 (5.4.3).

4⃣ Wiring of the power distributor

All remaining cables must be connected to the power distributor:
- Servo motor connection
- Arduino Nano R3
- WS2812B LED strip
- Hollow socket All connections are made with plus and minus (see 5.4.4 and 5.4.5).

5⃣ Using different colors and connection types for the wiring

It helps to use different cable colors:
- Red for plus
- Black for minus
The power distributor has different connection types:
- Male for plus
- Female for minus

6⃣ Note on the hollow socket

There is a separate article on wiring and connecting the hollow socket, which you should definitely read

7⃣ Attaching the connector housings for the servo motor and power supply

A three-pin plug is required for the servo motor connection.
A two-pin plug is required for the external power supply.

Further details on the construction process and the download links for connector housings can be found here.

Figure 5.5.1 shows the entire cabling again.

Arduino code

After the intensive work with the hardware and the 3D printer, we now turn our attention to the strategy and programming of the keypad lock. Why is a strategy important for a keypad lock? A well thought-out sequence of actions – i.e. the order in which the keypad lock is operated, which events result from certain actions and which goal is being pursued – forms the basis for functional control. This guideline is therefore also crucial for programming the keypad lock: it determines what should happen when and which hardware is used. The aim is to create a logical and comprehensible sequence of events, which in this case can also be understood visually.

Example 1:
The keypad lock should display how many digits have already been entered. (See Figures 7.0.1 to 7.0.4)

Example 2:
The keypad lock should indicate whether the password entered is correct after pressing a specific key. (See figure 7.0.5)

Example 3:
The keypad lock should indicate if something has been entered incorrectly, such as an incorrect password or too many keystrokes. (See figure 7.0.8)

Example 4:
The keypad lock should display the current status. (See Figures 7.0.5 to 7.0.7)

Now let’s move on to programming the keypad lock, which differs from conventional programs on the Internet in a few respects. To begin with, the three necessary libraries are included: for the keypad, for the WS2812B LEDs and for the servo motor (Figure 6.0.1). In the following section, the pin assignment for the LEDs is defined, whereby pin D10 is used and the number of LEDs and the color scheme are determined. The brightness of the LEDs is also defined – this value can be adjusted depending on the location, with higher values providing more brightness (values from 0 to 255). (See figure 6.0.2) The third section is dedicated to the description of the keypad used, including the number of rows and columns and the assignment of the buttons. (See figure 6.0.3).

In the fourth section, the servomotor is configured by defining the degree range it can cover and the speed at which it should move (see Figure 6.1.1). This is followed by the section for entering the password. Here you have the option of changing the default password 1516 to set a new four-digit password. The program will only work correctly if a four-digit code is entered. In this section, the control pin for the servo motor is also set to D9 (see Figure 6.1.2). The following section is dedicated to defining the colors for the various events.

The last two sections explain the behavior of the keypad lock during certain actions. This description is of course only a rough overview of the program. In a future article for keypad lock version 2, we will explain the program in more detail and more comprehensively.

//==========================================Librarys==============================================================
#include 
#include 
#include 
//========================================Neo-Pixel==============================================================
#define LED_PIN 10
#define LED_COUNT 3
Adafruit_NeoPixel strip(LED_COUNT, LED_PIN, NEO_GRB + NEO_KHZ800);
int led_strength = 75; //controlls Brighttness (0 - 255)
//========================================Keypad=================================================================
const byte rows = 4;
const byte cols = 3;
char keys[rows][cols] = {
 {'1', '2', '3'},
 {'4', '5', '6'},
 {'7', '8', '9'},
 {'*', '0', '#'}
};
byte rowPins[rows] = {8, 7, 6, 5};
byte colPins[cols] = {4, 3, 2};
Keypad keypad = Keypad( makeKeymap(keys), rowPins, colPins, rows, cols );
//=========================================Servo============================================================
Servo lock;
int pos = 0;
int servo_angle = 180;
int servo_speed = 15;
//======================================Password===============================================================
String input;
const String password = "1516"; //Set Password
int n = 1;

 

void setup() {
 input.reserve(password.length() +2);
 strip.begin();
 strip.show();
 lock.attach(9); //motor pin
}

void loop() {
//-------------------colours------------------------------------------------------------------- 
 uint32_t blue = strip.Color(0, 0, led_strength);
 uint32_t green = strip.Color(0, led_strength, 0);
 uint32_t red = strip.Color(led_strength, 0, 0);
 uint32_t orange = strip.Color(led_strength, led_strength/2, 0);

 char key = keypad.getKey();

if (key != NO_KEY) {
//-------------------------End conditions------------------------------------------------------
 if (key == '#') {
 if (input == password) {
 //unlock
 strip.clear();
 strip.fill(green, 0, LED_COUNT);
 strip.show();
 for (pos = 0; pos <= servo_angle; pos += 1) {
 lock.write(pos);
 delay(servo_speed );
 }
 while (1 == 1)
 { char key = keypad.getKey();
 strip.clear();
 strip.fill(orange, 0, LED_COUNT);
 strip.show();
 if (key == '*')
 {
 strip.clear();
 strip.fill(green, 0, LED_COUNT);
 strip.show();
 break;
 }
 }

 for (pos = servo_angle; pos >= 0; pos -= 1) {
 lock.write(pos);
 delay(servo_speed );
 }
 n = 1;
 input = "";
 delay (1000);
 strip.clear();
 strip.show();
 } else {
 //wrong password
 strip.clear();
 strip.fill(red, 0, LED_COUNT);
 strip.show();
 n = 1;
 input = "";
 delay (1000);
 strip.clear();
 strip.show();
 }
 }
 else if (n == password.length() + 1) {
 //Input too long
 strip.clear();
 strip.fill(red, 0, LED_COUNT);
 strip.show();
 n = 1;
 input = "";
 delay (1000);
 strip.clear();
 strip.show();
 }
//----------------------------------Buttons------------------------------------------
 else {
 input += key;
 if (n == password.length() ) {
 strip.clear();
 strip.fill(blue, 0, LED_COUNT); 
 strip.show();
 n++;
 }
 else {

 strip.clear();
 strip.setPixelColor(n-1, blue);
 strip.show();
 n++;
 }
 }
 }

}

Function

Operating the keypad lock is very intuitive. As soon as the first button is pressed, the right-hand LED lights up blue (7.0.1). When the second button is pressed, the middle LED turns blue (7.0.2). After the third button is pressed, the left-hand LED lights up blue (7.0.3). Finally, with the fourth button, all three LEDs light up blue (7.0.4). When these three LEDs light up blue, the user knows that the # button must be pressed.

If the # button is pressed, the password is checked. If the password is correct, all three LEDs light up green at the same time and the servomotor is activated (7.0.5). The green light remains on as long as the servomotor has not yet reached its end position (open). As soon as the servomotor reaches the end position (open), the LEDs change from green to orange (7.0.6). The orange color remains until the user presses the * button.

After pressing the * button, the LEDs change back to green (7.0.7) and remain in this color until the servomotor has reached the end position (closed). If this is the case, the LEDs go out and the keypad lock is ready for new entries.

However, if the password is incorrect after pressing the # button in step 7.0.4, all three LEDs light up red (7.0.8). The red light is also displayed if more than four buttons, apart from the # button, are pressed.

Door mounting

Of course, this variant is not intended for use on an ordinary door, where you simply walk through and the door closes by itself. The reason for this is that the lock remains open until the * button is pressed. But how can you press the * button when you are on the other side of the keypad lock, behind the wall? A delay in the program could help, but who knows how long it takes to pass through the door and close it behind you? A much more sensible solution would be to implement an additional switch that is placed on the other side of the door. When pressed, this switch would lead directly to point 7.0.6 and open the lock so that the door can be opened from the inside without having to enter a password.

But that’s for the future. Now we come to mounting the keypad lock on a door. I have provided four holes on the back of the housing for this purpose. These holes have a recess on the inside for conventional hexagon nuts M4 DIN 934. The corresponding holes can be seen in Figure 8.0.1 (rear view) and Figure 8.0.2 (front view), whereby the housing is shown slightly transparent for better visualization. Installing the nuts is very simple: After ensuring that all support material has been removed, the nut is pressed into the recess provided from behind. Press-in nuts should not be used as they are unnecessarily expensive.

I have developed a drilling template for fixing to the wall or door (Fig. 8.0.3). This template contains a hole with a diameter of 4 mm at each of the four corners. The distance between the holes corresponds to the distance between the holes on the housing. The template can be easily fixed to the surface of the door, for example with adhesive tape (Fig. 8.0.4). This saves you the tedious task of marking out the drill holes and avoids errors.

Figure 8.1.1 shows the drilled mounting holes from the front, marked by magenta-colored circles. Thanks to the drilling template, these holes are the correct distance apart. If the position slips slightly during drilling or is not exactly correct, this is not a problem. In this case, you can simply drill the mounting holes slightly larger to align the keypad lock precisely when screwing it on. In addition, two holes can be seen in yellow circles in this picture, which are unfortunately slightly broken out at the edge. These holes are intended for the servo cable and the power supply. Once the holes had been drilled, I fitted the keypad lock and fed the cables through the holes provided on the back of the door (Fig. 8.1.2).

The entire assembly of the keypad lock is shown on the front side of the door in Image 8.2.1. If you are not satisfied with this mounting solution, don’t worry: As a final step, I have designed a back cover that allows the keypad lock to be mounted on a wall or frame (Image 8.2.2). To do this, simply place the housing of the keypad lock onto the back cover and secure it from behind using M4 countersunk screws (marked by magenta circles in Image 8.2.2). After that, the entire construction is mounted on the wall, for which two tabs with two holes each are available (yellow circles in Image 8.2.2).

It is also important to remember to add one or more openings in the housing for the servo and power supply cables. Additionally, the security risk should be considered, as an unauthorized person could potentially unscrew the keypad lock using the accessible screws.

Locking Mechanism

If you’re still missing a real locking mechanism that goes beyond just a servo connection, you can look forward to the “Locking Unit,” which is already in development and will be featured in future versions of the keypad lock.

The development of the keypad lock was an exciting yet challenging task. Some key features of VERSION 1 of the keypad lock are particularly noteworthy:

Compatibility with various Arduino Nano models and adapters – Ensures flexibility in hardware selection.
Visual feedback – Users are directly informed about number input and the status of the keypad lock.
Emergency power supply via barrel jack – Guarantees reliable operation in case of power failures.
Stable software – Developed to ensure reliable functionality.
Optimized ergonomics for both left- and right-handed users – Designed for comfortable use by all users.

Files for Download

Keypad lock housing

The post DIY keypad lock – 3D printing and code appeared first on Nerd Corner.

Mini Digital Voltmeter

Nerds — Wed, 09 Oct 2024 15:02:19 +0000

If you want to measure voltage with a voltmeter or multimeter, you normally need two hands. But usually you only have one hand free. You can of course use crocodile clips or similar to help you, but this is usually awkward. Especially in experimental setups, you often have to measure the voltage at different points to analyze the behavior of the circuit.

The solution to my problem is the mini-voltmeter, which I have used many times in various projects in the past. The accuracy of the mini-voltmeter is usually sufficient and my projects tend to be in the low-voltage range. In addition, the mini voltmeters are relatively inexpensive and you can get them everywhere.

I also use USB multimeters to measure voltage and current, which save the values at the same time. Figure 1.0 shows some USB multimeters that can handle more or less voltage. Some devices are very expensive and the maximum number of amperes that can be measured also varies. If you only want to measure voltage and don’t have much of a budget, my project is just right for you.

This might also interest you: Do it yourself power bank with voltage regulator and voltmeter

List of components

Mini voltmeter DSN-DUM-368 /or DSN-DMU-368k (Figure 2.0.1)
Hollow socket 5.5×2.1 (Figure 2.0.2)
Hollow plug 5.5×2.1 (image 2.0.3)
USB micro adapter board optional (picture 2.0.4)
M2 x 10 countersunk head screw 6x (without picture)
M2 x 4 cylinder head screw 2x optional (without picture)
Cable 0.5mm² (without picture)

As can be seen in Fig. 3.0, there are two different types of mini voltmeters. The one with two cables (Figure 3.0.1) and the one with three cables (Figure 3.0.2).
The main difference is that with the mini-voltmeter with two cables, the supply voltage is the same as the voltage to be measured (Figure 3.0.1).

However, there is a problem with this variant. If the voltage is below 4.7V, the mini-voltmeter will no longer work as it requires a supply voltage of at least 4.7V. So if you want to measure a voltage below 4.7V, you need a supply voltage above 4.7V and a separate cable to measure the voltage (Fig. 3.0.2).

You can also convert a mini-voltmeter with three cables into a mini-voltmeter with two cables. You only need to solder a bridge between +Ub and input at jumper-1 (Figure 3.1.1). Jumpers two to four are used for fine adjustment of the mini-voltmeter (Fig. 3.1.1), in some cases the step widths are printed on as in Fig. 3.0.1.
How such a mini-voltmeter is constructed in detail is documented here or here for example.

Construction

Because of these two different types, I have decided to construct two housings. Let’s start with the variant for the two-cable mini-voltmeter. In the past, I have installed mini-voltmeters in enclosures several times and in doing so have become familiar with the challenges of dimensional accuracy and the diversity of variants from different manufacturers. Despite supposedly standardized components, you often have to reckon with slight deviations in the dimensions. It is therefore important to take larger tolerances into account in the design.

One of the housings I designed was intended for the LM2587 step-up module (Figure 3.2.1). This housing seemed suitable for modification to meet the new requirements. It already contains holders for the hollow plug (2.0.3) and the hollow socket (2.0.2) that I want to use. There is also already a recess in the cover for the mini voltmeter (2.0.1). I am largely satisfied with the dimensions (Figure 3.2.2), apart from the length. What bothers me, however, is the position of the voltmeter in the lid – it should be placed more centrally, i.e. closer to the middle.

First I start with the modification of the lid. I’m happy with the width and height, but the housing is too long. I therefore shorten the cover on the side where the hollow socket (2.0.2) is attached. This does not affect the holder of the hollow plug, as this is already perfectly matched to the plug. When shortening, care must be taken to ensure that the internal components do not touch and that there is sufficient space for the cabling. However, you should not overdo it with the reduction in size, as stability and feel are also important factors in a design.

After weighing up all the factors, I shorten the length of the housing or cover to 63.5 mm, and the position of the mini-voltmeter is now centered on the cover (Figure 4.0.1). I have removed the hole for adjusting the LM2587S (marked in white) and the ventilation slots, as no adjustment is required and no ventilation is necessary due to the low heat development.

In picture 4.0.2 (marked in red) you can see that I have changed the recesses or pockets, as some mini voltmeters have a flat surface instead of tabs (picture 4.0.3).

In the next step, I shorten the housing to 63.5 mm, similar to the cover. I also remove the mounting pillars for the LM2587S module, as shown in Figure 4.1.1. On the side of the hollow socket, I remove the recess and move the hole pattern 1 mm upwards, towards the cover (Fig. 4.1.2). Finally, the lettering is corrected to VOLT METER.

3D print of the first variant

Let’s move on to printing the parts for our variant 1 with two cables. We only need three parts for this variant:

Housing Fig. 5.0.1
Cover Fig. 5.0.2
Hollow socket holder Fig. 5.0.3

There are no special requirements for printing these parts and no special material is needed. In this case, I used inexpensive PLA from a reliable manufacturer. The printing was done on a Prusa MK4 with the usual standard settings.

When reworking the printed parts for variant one, only four M2 threads need to be cut into the housing (Fig. 6.0.1) and two M2 threads on the mounting bridge for the hollow bushing (Fig. 6.0.2). Two M2 threads must also be cut in the cover (Figure 6.0.3). Alternatively, self-tapping screws can be used or the parts can be partially glued.

Soldering and wiring the first variant

Once all the parts for variant one have been printed and processed, the hollow socket is soldered to the cables. The positive and negative poles to which the cables are soldered are marked in Figure 6.1.1 (Figure 6.1.2). The cables of the hollow socket and the mini voltmeter are then screwed into the hollow plug (Fig. 6.1.3). Whether the cables are twisted or soldered at the ends is a matter of taste. I always connect the cables of the mini-voltmeter to the current output. Figure 6.1.4 shows the complete inner workings soldered and wired. To stabilize the solder joints on the mini-voltmeter, I reinforced them with a small drop of hot glue. Finally, the hollow socket is inserted into the back of the housing and the hollow plug is pushed into the recess provided (Fig. 6.1.5).

In the penultimate step, I push the mini-voltmeter into the cut-out provided in the cover and secure it by screwing or gluing it in place (Fig. 6.2.1). The cover is then screwed to the housing (Figure 6.2.2). Finally, carry out a function test (Figure 6.2.3).

Construction of the second variant

If you do not want to measure or display the voltage below 4.7 V with the mini-voltmeter, you can stop at this point. However, as I mentioned at the beginning, it is possible to operate these mini-voltmeters with three cables. This option is available if jumper1 (Figure 3.1.1) is not set or not bridged. As the mini-voltmeter requires a minimum supply voltage of 4.7 V in order to function, we need a second voltage source that is above this limit.

In variant one of the housing, however, there is only one input, which is why a second current input is required. As I don’t want to change the dimensions of the housing and there is hardly any space for a second hollow socket, an alternative solution is needed. The solution is a micro-USB board (Figure 2.0.4), which is flat and based on the widely used micro-USB standard.

The question now arises as to where the second connection should be positioned. A side connection would take up too much space, e.g. on a table, as the cable would protrude upwards or downwards at a 90° angle. For me, the best solution is to place the USB port on the same side as the hollow socket.

The next question concerns the mounting of the micro USB board: should it be attached directly to the housing or simply glued on? After careful consideration, I decided to mount the board on the retaining bridge of the hollow socket (Figures 5.0.3, 6.0.2 and 7.0.1). In picture 7.0.2 you can see how I attached a plate to the holder bridge. This plate has two M2 threaded holes (marked in white) for attaching the micro USB board and two cut-outs for cables and solder.

On the housing (Figure 7.0.3), the drilling pattern (marked red) must be moved 1.5 mm towards the cover to create space for the slot of the micro USB connector. The slot (marked yellow) is positioned below the hollow socket.

Printing is relatively quick. We need the housing with USB slot (Fig. 8.0.1), the cover (Fig. 8.0.2) and the new holder for the hollow socket and USB board (Fig. 8.0.3).

In the post-processing of the printed parts for variant “two”, the thread must now be cut. M2 4x on the housing (Fig. 9.0.1) and 4x M2 mounting bridge for the hollow socket and USB board (Fig. 9.0.2). Two M2 threads must also be cut on the cover (Fig. 9.0.3).

Soldering and screwing the second variant

The parts must now be soldered and screwed together, as in variant one (Fig. 6.1). It should be noted that there is now an additional cable and the wiring is different to variant one. The mini-voltmeter is now powered externally via the micro-USB connection. The negative pole is routed from the hollow socket (9.1.3) to the USB board (9.1.1), then to the mini-voltmeter (9.1.2) and finally to the hollow plug (9.1.4).

The positive cable for the power supply of the mini-voltmeter (9.1.2) goes from the positive pole of the micro USB (9.1.1) directly to the positive pole of the mini-voltmeter (9.1.2). The main power cable runs from the positive pole of the hollow socket (9.1.3) to the positive pole of the hollow plug (9.1.4). The test lead runs directly from the mini-voltmeter (9.1.2) to the positive pole of the hollow plug (9.1.4).

Figure 9.2.1 shows how to screw the USB board (9.1.1) to the hollow socket holder (9.0.2). Figure 9.2.2 shows the hollow socket 9.1.3 and the USB board 9.1.1 completely soldered, screwed to the hollow socket holder and then fixed again with hot glue. The result can be seen in picture 9.2.1.

After successfully soldering and gluing, I assemble the mini-voltmeter variant “two”. First, I insert the retaining bridge for the hollow socket and USB board into the back of the housing and screw it in from the outside (Fig. 9.3.1).

The hollow plug is then inserted into the recess provided and pressed down to the bottom (Fig. 9.3.2). Now press the mini-voltmeter into the cover and either screw or glue it in place (Fig. 9.3.3). Finally, the cover is fitted and screwed on with the M2 screws (Fig. 9.3.4).

Function test

Now it’s time for the essential function test. For this we need a micro USB power supply unit and a 12V power supply unit with a 5.5×2.1 mm hollow plug. First, I connect the micro USB power supply, which supplies 5V, to the housing. The display of the mini-voltmeter lights up and shows zero (Figure 9.4.1). This is the expected result, as there is still no voltage on the line to be measured. Only when I connect the 12V power supply unit with hollow plug does the mini-voltmeter correctly display 12V (Fig. 9.4.2).

Everything works perfectly and adds value for me in the workshop.

Files to download

Mini digital voltmeter

The post Mini Digital Voltmeter appeared first on Nerd Corner.

Dupont Connector V1.1

Nerds — Wed, 14 Aug 2024 09:10:06 +0000

In response to the extremely positive feedback on my quick connectors (Dupont connectors), I realized that their original purpose of only being used in the development environment has been extended to permanent use on various devices. Many people also expressed the wish to be able to mount the connectors permanently or screw them on. I have now fulfilled this wish.

You may also be interested in: 3D printed Dupont connector for jumper cables

Implementation of the Dupont connector

As with any new development or modification of an existing part, a number of decisions had to be made, but in this case not many were necessary.

Number of fixing lugs: two or four
Diameter of the fixing holes: 2.2 mm
Cover removable after fastening: yes

With the number of fixing lugs, it is clear that a single lug will cause the housing to rotate around the screw if it is not tightened firmly enough. When the connection is inserted or removed, the housing tries to rotate around the screw. With two or more tabs, insertion and removal can be achieved without any problems, even if the screws are not fully tightened.

The diameter of the fixing holes has been set at 2.2 mm for M2 screws. Larger screws would make the lugs larger than the connector housing itself, and two M2 screws already provide sufficient holding force.

The decision as to whether the cover should still be removable after the connector had been attached was inevitable. As the clamping tabs of the cover protrude from the base of the housing, the fastening tabs had to be raised above the base anyway. If the lugs were flush with the base of the housing, the lid could rise by around 0.3 mm when the screws were tightened. Why were the fixing lugs not attached directly to the lid? The lid is not stable enough to support the side tabs. The distance between the surface and the base of the housing is 1.1 mm when screwed on, which is sufficient to remove the lid without any problems.

Regarding the fixing holes with a diameter of 2.2 mm: The hole spacing is always a multiple of 2.54 mm, which makes sense as the DuPont plugs also have a width and height of 2.54 mm. The hole spacing increases in proportion to the number of pins on the housing. A positive side effect: These distances also match the holes of a breadboard. In Figure 1.0.1 I have mounted two 4-pin connectors on a breadboard. For the attachment, I used the matching holes at the distance of the 4-pin connectors and cut threads with an M2 tap. As you can see, the screws hold perfectly without the need for a nut.

Yes, that’s almost it for this time – we’re actually finished now, but two things are still important to me. Firstly, I would like to talk about the versatility of the connectors. I’ve been using them for four years and am constantly discovering new ways to use them flexibly. Below are some examples with version one, which is identical to version 1.1 except for the screw-on option.

Figure 2.0.1 shows a 10-PIN connector with a 200 mm jumper cable. Figure 2.0.2 shows the difference between a 10-PIN connector with a 100 mm jumper cable and one with a 200 mm jumper cable.

Figure 2.1.1 shows a 9-PIN connector on one side and three different connectors on the opposite side. Figure 2.1.2 shows this side enlarged. Here you can see the three connectors: a 4-PIN connector, next to it a 3-PIN connector and on the far left a 2-PIN connector. If you add up the pins of the three connectors, you get the nine pins as on the other side.

You have probably noticed that the DuPont plugs of the three connections are different. On the 4-PIN connector, all pins are male, i.e. pins. In contrast, all pins on the middle 3-PIN connector are female, i.e. sockets. The 2-PIN connector, which combines a male and a female connector, is particularly interesting. What is it all about? Here I would like to demonstrate the flexibility of Nerd-Corner’s tool-free connector system. As with the 2-PIN plug, these plugs can be used to install reverse polarity protection: The pin is the positive pole, the socket is the negative pole. The reverse is true for the mating connector, which means that the connection cannot be plugged in incorrectly!

The 2-PIN plug is the simplest example, but this principle can be applied to all plugs so that more complex protection systems can also be set up.

The structure in Figure 2.2.1 shows another way of creating a wiring harness. There is a 10-PIN connector on the left-hand side and a 5-PIN connector on the far right, connected by a 200 mm jumper cable. The orange 3-PIN connector is connected to the 10-PIN connector via a 400 mm jumper cable, as is the 2-PIN connector, but with a 500 mm jumper cable. This solution offers unlimited flexibility across the entire connector family and is completely tool-free.

Assembling the Dupont connector

I keep getting requests to build connector housings for 15 or 22 pins. Unfortunately, this is not impossible with this system, but it is a major challenge. The effort involved is disproportionate to the benefit – at least for me. I actually wanted to stop at the 6-PIN version, as the assembly requires a lot of fine motor skills and the holding force of the tabs decreases. I was able to solve the problem of the holding force from the 7-PIN version onwards by using a third tab, but this made assembly very difficult.

However, there is usually a solution, as can be seen in picture series 3.0.

In picture 3.0.1 you can see that a female connector comes into play, as we are using male (pin) cables here. A pin header could be used instead for female cables.

The procedure for assembling with male cables (pins) is as follows:

Push the cables into the socket strip.
Press the inserted DuPont housings lightly into the base of the connector and press the cables into the recesses provided (see Fig. 3.0.1).
Press the DuPont housings fully into the base of the housing and push them towards the internal stop strip. Then pull the cables backwards one by one – the socket strip should not be removed (Fig. 3.0.2).
As soon as the DuPont plugs are fixed in the housing, the cover is fitted and snapped into place (Fig. 3.0.3).
Finally, the socket strip is removed and the assembly is complete (Fig. 3.0.4).

Files to download

Dupont Connector 3PIN

The post Dupont Connector V1.1 appeared first on Nerd Corner.

Using a barrel jack as a switch

Nerds — Tue, 18 Jun 2024 17:11:28 +0000

In many everyday devices, such as battery-operated radios, lamps, torches and especially laptops, a barrel jack is used for the power supply. In these cases, the barrel jack often serves as a switch: as soon as a plug is inserted, the power supply from the battery, rechargeable battery or other source is interrupted and the device is supplied with power directly from the plug, thus saving the battery. The primary circuit is disconnected purely mechanically.

This might also be interesting for you: Do it yourself powerbank with voltage regulator and voltmeter

List of components

To demonstrate the function, I have decided on a small test setup. I need the following for my test setup:

Barrel jack 5,5 x 2,1 (1.0.1)
Voltmeter (1.0.2)
5V power supply unit (1.0.3)
Barrel jack holder (1.0.4)
Barrel jack Bridge(1.0.5)
Some cables (1.0.6)

Assembly instructions for bracket and bridge

The first step is to print the holder (1.0.4) and the bridge (1.0.5) with the 3D printer. After cleaning the printed parts, I cut two M2 threads into the holder (see 2.0.1). If you prefer to work with self-tapping screws, you can skip this step. The barrel jack is then pushed into the large hole in the bridge (2.0.2) and screwed tight with the nut on the front of the bridge (2.0.3). Fitting the bridge to the bracket is also very simple: Slide the bridge with the recesses on the right and left over the two cylinder surfaces on the bracket (2.0.4) and secure it with M2 screws (2.0.5). The bracket and bridge with the barrel jack fitted form a very stable unit that can absorb large forces. If everything is fitted correctly, the barrel jack should not protrude, but should be recessed by 0.3 to 0.5 mm.

Wiring and soldering the barrel jack

Now we come to the core of this article: wiring and soldering the barrel jack. I use pre-assembled plugs and sockets that already contain crimped cables and a strain relief. The colour coding of the cables is also practical, as red stands for plus and black for minus (3.0.1).

The barrel jack with switching function usually has three solder lugs. The negative pole is always switched, i.e. in figure 3.0.2 this corresponds to number two. The negative pole of the primary power supply, e.g. battery or accumulator, is also soldered on here. Solder lug number one is intended for the common positive terminal; all positive connections are soldered here. The negative pole to the consumers in the device is soldered to soldering lug number three. Figure 3.0.3 shows the complete soldering of the barrel jack.

Assembly and connection

After successful soldering, you can now continue with the rest of the test setup. Firstly, the holder with the soldered barrel jack is screwed onto a wooden plate (4.0.1). The two mini-voltmeters are then attached to the wooden plate (4.0.2). The mini voltmeters are a creation of Nerd Corner. If you are interested in such housings, you can read the corresponding article and download the STL files at the following link.

Now I connect the cables soldered to the barrel jack to the mini-voltmeters (see Figure 4.0.2, pink frame). Next, I connect the primary power source to my 5V power supply and switch it on (see Figure 4.0.3, yellow frame). After switching on the power supply, a voltage is present at both mini voltmeters: 5.35 volts at the supply (red circle) and 5.28 volts at the load (green circle).

Integration of the second power source

As the current flows cleanly via the barrel jack to the consumer, the second power source now comes into play. I operate this with 12 V in order to have a clear difference to the primary power supply. Figure 4.1.1 shows the second power supply with 12.2 volts (turquoise frame).

Now I plug the second power supply with 12 volts into the barrel jack (Figure 4.1.2, blue frame). After a short delay, the value on the consumer’s mini-voltmeter changes to 12 volts (green frame). Nothing has changed on the primary power supply; it remains plugged in and switched on (red frame). The value is still 5.34 volts, which is 0.01 volts lower than before the second power supply was plugged in, but this is due to the fluctuations of the 5V power supply.

As a final step, I remove the 5 volt power supply unit from the primary circuit to check whether there really is no voltage on the primary circuit. Figure 4.2.1 in the yellow frame remains dark and so the test was successful!

Files for Downloading

Barrel jack holder and bridge

The post Using a barrel jack as a switch appeared first on Nerd Corner.

3D Printed Tealight Holder

Nerds — Mon, 25 Sep 2023 11:37:52 +0000

Tea lights are practical and create a pleasant Christmas atmosphere. Meanwhile, LED tea lights are also very popular. They usually have a battery as their energy supply. They are often operated with the CR2032 button cell. This has a voltage of 3V and the tea lights light up between 3 and 8 hours with one battery charge. After that, you have to change the battery. This bothers me because it is a lot of work and I have a guilty conscience. I would find it better to supply the tea lights with power permanently via a cable.

You might also be interested in: 3D printed battery container

List of components

LED tealightset
Button cell CR2032
Jumper cables
Screws

Procedure

First, I ordered a set of LED tea lights. I measured it and examined whether it could be connected to a cable. I was quite surprised by the technique of how the LED gets power from the battery. It is simple but well thought out! With the on/off switch, a metal pin is pushed to the edge of the battery. This edge is the positive pole. The other metal pin is fixed in the housing and permanently touches the bottom of the battery. The bottom is the negative pole. The metal pins reminded me of pins on jumper cables. You can see how I connected the cables to the tea lights in the following series of pictures.

First, the cover and contact foil must be removed. Then the battery is removed.

The two current collectors are now visible in the battery compartment. The negative pole is brought into the vertical position using a screwdriver or pliers.

Then remove the black plastic cover (female) from both jumper cables with side cutters. But be careful not to damage or crush the metal clamps!

A jumper cable is pushed over the pin at the positive terminal and at the negative terminal and pressed on. Afterwards, the holding capacity of the press connection should be tested. When the metal clamps are firmly seated on the pin, the function of the LED should be checked. For example, by removing the battery.

The cables are fixed with hot glue. Finally, after checking the function of the LED again, I attach a connector housing to the cables. You can find out how to construct such a connector housing here.

Secondly, I need a holder for my wired tea lights. I want to design the holder myself on the CAD and then print it out on the 3D printer. You can see how to design such a tea light holder in Solidworks in the video below:

After the tealight holder has been designed and printed, it is painted. Then the wired LED tea light can be mounted in the holder. Of course, the holder should be properly deburred beforehand. You can see the procedure in the next picture.

When using the tealight holder shown here, make sure that the cables are fed through the hole provided for this purpose. Please also take care to insert the cables one after the other into the hole in step 6.4.

Power supply

The third step is the power supply for the tea lights. For this I use a USB power supply with 5V and a step down module like the LM2596s. The voltage converter is supposed to provide me with the 3V that the tea lights need. Fortunately, I have constructed some housings for the LM2596 in the past that I can use here.

With the LM2596 used here, I reduce the voltage from the USB charger from 5V to 3V for the LED. You can also apply a voltage of less than 3V, in which case only the luminosity of the LEDs is reduced. The arrangement of the holders in the picture is only an example.

If you need an independent power source, e.g. a power bank, you can use my power bank with 3V output.

Assembly

Different screws can be used for mounting the tea light holders. Depending on the surface, you can use wood screws or cylinder head screws, for example. Alternatively, you can also screw the holder directly to the wall with the help of dowels. The only thing to note is that the screw head must be larger than 7 mm and smaller than 11 mm in diameter. The hole for the screws has a diameter of 5 mm. The hole for the cables lies vertically on the centre line of the screw hole and the centre distance to this is exactly 7 mm. The diameter of the cable hole is 4.5 mm.

Files for download

Tealight holder

The post 3D Printed Tealight Holder appeared first on Nerd Corner.

DIY powerbank with voltage regulator and voltmeter

Nerds — Fri, 24 Feb 2023 22:02:44 +0000

After building a simple powerbank, I now decided to combine a step-up module XL6009 with my existing powerbank. Fortunately, I had already constructed and tried three different case variations for the XL6009 in the past. The picture below shows these three different case designs. As usual, the cases can be downloaded individually via a link at the end of the post. The exact procedure for constructing the enclosures has already been described in detail in the article about the LM2587S.

You might also be interested in: DIY Powerbank with the Battery Shield V3 and Lipo Battery 18650

List of components:

2 x Hollow socket 5.5 x 2.1
1 x Battery Shield V3
1 x LiPo 18650 3500mAh
1 x rocker switch 250V/3A mounting dimension 15×10,5mm
4 x hexagon socket head screws M2 x6
6 x raised countersunk head screws M2 x 12
1 x module XL6009
1 x Mini voltmeter DSN – DVM – 368
7 x jumper cable

Implementation

Basically, the XL6009 differs from the LM2587S only in terms of current. The XL6009 provides an output voltage of 5V-35V and an input voltage of 3V-32V at 2.5A output current. To operate at 3A output current the XL6009 must be cooled with a heatsink. My choice fell primarily due to the small dimensions and the low price on this module. Since the capacity of the LiPi battery is limited, there is no need to install a too large step-up.

Construction

The Battery shield V3 has already been analyzed in detail here. Therefore we can start directly with the construction of the case. The case of the last powerbank is used as a basis, because the mount for the Battery shield V3 is already included. Now the two hollow sockets, the XL6009 and the mini voltmeter have to be integrated. There seems to be enough space for the hollow socket at the XL6009 output to be placed vertically above the USB Micro input.

For this project only the height of the case has to be increased. The raise also helps to fix the second hollow socket in the lid at the front. The position of the hollow socket with a mounting bridge is placed vertically as well. The hollow bushing for the XL6009 output is screwed from the outside. The hollow socket for the 3V output from the inside. This is important because two different hollow socket mounting bridges are needed. For a better overview the following illustration is provided:

I have added a new mounting part for the XL6009 module. It is a holder that is attached to the inner wall of the case. So the module can be screwed tightly from the outside. A disadvantage is the fact that the holder with module covers the LiPo and when changing the LiPo battery, the step-up must be removed at first. Ideally, though, the battery is rarely changed.

The lid was raised a bit compared to the simple powerbank and one or two crossbars were removed. This created space for the mini voltmeter. To be able to adjust the XL6009 without removing the lid, another hole was needed in the lid.

To set the hole as ideal as possible, it helps to assemble the case physically at first. So you can move the position of the XL6009 module on the mount a bit because the module has a 3mm hole and the mounting screws with M2 leave a little space.

To be able to turn the XL6009 on and off, a switch was still necessary. Here I opted for an ordinary toggle switch. Overall, I am satisfied, because the housing has increased by only 12mm compared to the other powerbank and the dimensions in width and length have remained the same.

Step by step assembly

Purpose of the powerbank

The powerbank obviously can charge smartphones and headsets via the USB A, just like any other powerbank. The 3V output can be used to power common flashlights or electronic modules. In addition, the adjustable voltage output can cover a range from 6V to 30V. There are many devices which are operated with 6V, 9V and 12V e.g. LED, radio etc..

I have specified the top voltage value up to 30V, but the XL6009 module could at least handle 35V. However, the mini voltmeter that I use is only specified up to 30V. Another reason is the Battery Shield V3 itself. For the Shield, the output is described as 5V and 3A, but the reality is lower than that. The reason is the internal voltage converter which brings the LiPo voltage to 5V.

The following table contains measured values that show the relationship (without internal voltage converter) between the increase of the ampere value at the input and the voltage value at the output:

State of charge in volt
Volt for 1A	3,2	3,7	4,2
6	1,88	1,62	1,43
7	2,19	1,89	1,67
8	2,50	2,16	1,90
9	2,81	2,43	2,14
10	3,13	2,70	2,38
11	3,44	2,97	2,62
12	3,75	3,24	2,86
13	4,06	3,51	3,10
14	4,38	3,78	3,33
15	4,69	4,05	3,57
16	5,00	4,32	3,81
17	5,31	4,59	4,05
18	5,63	4,86	4,29
19	5,94	5,14	4,52
20	6,25	5,41	4,76
21	6,56	5,68	5,00
22	6,88	5,95	5,24
23	7,19	6,22	5,48
24	7,50	6,49	5,71
25	7,81	6,76	5,95
26	8,13	7,03	6,19
27	8,44	7,30	6,43
28	8,75	7,57	6,67
29	9,06	7,84	6,90
30	9,38	8,11	7,14

One should not forget that with battery-powered voltage converters, the voltage drop during discharge is also a factor. In order to be on the safe side, I have installed a pico fuse with 2A in this powerbank. Attached is a table with ampere values that should not be exceeded by the consumer at the specified voltage:

Volt	max. A consumer
6	1,67
7	1,43
8	1,25
9	1,11
10	1,00
11	0,91
12	0,83
13	0,77
14	0,71
15	0,67
16	0,63
17	0,59
18	0,56
19	0,53
20	0,50
21	0,48
22	0,45
23	0,43
24	0,42
25	0,40
26	0,38
27	0,37
28	0,36
29	0,34
30	0,33

Download Files

The post DIY powerbank with voltage regulator and voltmeter appeared first on Nerd Corner.

Glare free lamp and powerbank

Nerds — Mon, 26 Dec 2022 15:31:51 +0000

I bought a new 3D printer with a closed build chamber. At some point I noticed that one of the two extruders was clogged. The issue was, to unclog the extruder I needed light, because the build room light only works when the printer is on. When the printer is on, the fans would also start spinning, and those can quickly break if you slip off with the hex key. Therefore, I preferred to use a flashlight.

The flashlight was hard to position properly and it dazzled. For this reason, I came up with the idea of developing my own glare-free lamp, which you can simply place on the heating bed and is not blinding. Preferably wireless with a powerbank. I had already built my own powerbank with the Battery Shield V3, which I used as a basis this time.

This might also be interesting for you: Own powerbank with the Battery Shield V3

List of components

1 x Hollow socket 5,5×2,1
1 x Battery Shield V3
1 x LiPo 18650 3500mAh
1 x rocker switch 250V/3A mounting dimension 15×10,5mm
4 x hexagon socket head screws M2 x6
6 x raised countersunk head screws M2 x 20
17 x 5V SMD2835 LED strips
5 x jumper cable

Choice of LED

Since the basic housing of the powerbank with the Battery shield V3 was already finished, I mainly had to think about the lighting. LEDs with 5V or 3V should be used as illuminants, because the Battery shield V3 provides either 5V or 3V. For my purposes a lower lumen value is sufficient. After a short research I found suitable LED strips.

The light temperature of my LED strip is 6500K also called cold white. This light contains a lot of blue, which makes it easy to work with and details become visible quickly. Since the Battery shield V3 has three additional 5V and one USB A output, powering the LEDs is no problem.

The LEDs for the glare-free lamp are SMD2835. These are 2.5 mm wide and 3.5 mm long and have a slightly lower luminosity than a SMD5050. How much the LEDs consume is critical to the lamp’s burn time, as the power supply from the battery is limited.

Construction of the cover and middle cover

As already mentioned in the previous section, the base case of the powerbank is not changed. Instead, the LEDs are glued onto an inner cover. The middle cover also serves as a support for the hollow socket for the 3V output. Furthermore, a breakthrough was contructed to pass through the cables from the on-off switch. The slanted openings of the intermediate cover should help to apply adhesive to the LED strips from behind if necessary.

For the top side (the lid, where the light shines through) it became a little more complex. On the one hand, enough light should shine through, but on the other hand, it must not dazzle! Of course, a crystal clear lid would be ideal for the light yield, but as I said, then it would possibly dazzle. To strike a balance between effective light output and freedom from glare, several factors must be taken into account:

Material selection (filament)
Distance to the light source
Thickness of the lens
Printing strategy

The choice of material for the anti-glare lamp was “ivory”. The distance to the illuminant is 10.5 mm and the layer thickness (material thickness) is 1 mm. The layer height is 0.25 mm, i.e. one millimeter results in four layers, with the first layer applied 45° to the left and the second layer 45° to the right. Due to the different directions of the layers, the light is refracted again and again and becomes glare-free. This is a subjective perception and the designation glare-free therefore does not apply to all people.

Assembly

Soldering the parts to the jumper cables:
Cutting and gluing the LED strips: The LED strip is separated into two times 6 LEDs and once 5 LEDs and glued to the intermediate cover. The cable opening on the lid for the plug must remain free:
Attach the hollow bushing to the intermediate cover:
Screw the battery shield into the housing after the ten threads have been previously cut into the housing.
Press the rocker switch into the cover:
Press LiPo 18650 into the receptacle
Connect cable and turn on:
If all LEDs light up, place the middle cover on the housing and then place the cover on the middle cover and screw it down:

Glare free lamp CAD design

For the threads, the holes are designed for core hole diameter, i.e. for M2 for diameter 1.6 mm. You can tap the thread with the tap or form (press in) with a screw. Personally, I prefer the thread cutting. The two graphics show where the threads have to be cut on the housing.

Further notes

Some may wonder why the rocker switch sticks out of the lid and is not recessed. It makes it easier to turn the lamp on and off. Most of the time you only have one hand free and can’t really reach into the recess, but if the rocker switch sticks out it’s easier to operate it. Nevertheless, I have also designed a version with recessed rocker switch, which you can download in the download section!

The power of the lamp is about 1.4 watts. At 5.05 V the current is therefore 0.27 A, which is no problem for the Battery Shield V3 and the LiPo. The burn time of the lamp is about 5 hours in continuous operation. For this data, I used a Samsung 18650 with 3500 mAh. The powerbank can be used in parallel to run the lamp. However, the total current should not exceed 3A.

I use this lamp not only for my 3D printer, but also for soldering, reading or as a night light. The powerbank is also extremely light with 127g.

Download files

STL files of the glare free lamp

The post Glare free lamp and powerbank appeared first on Nerd Corner.

3D printed Dupont connector for jumper cable

Nerds — Fri, 27 May 2022 10:10:38 +0000

Many DIY projects are accompanied by chaos at the workbench. Screwdrivers, soldering irons, jumper cables, everything lies all over the place. Clean up is usually only at the end of the day or when the project is finished. I was annoyed by this mess, especially the jumper cables were everywhere. After I designed a connector as a soldering aid for jumper cables and LED strips, I came up with an idea with which I could both get the chaos under control and increase the stability of the jumper cable PINs. The idea was to use a Dupont connector.

The following picture shows such a connection. I am absolutely thrilled with how practical these connectors are in everyday life. For example, several LED strips can be connected via a 4 PIN Dupont connector to a controller without any additional tools!

This might also be interesting for you: designed a connector as a soldering aid for jumper cables

List of components:

3D printer
Filament PLA
Jumper cables

CAD design for Dupont connector

As with any CAD design, you shouldn’t just start off without a plan, but rather clarify a few questions first.

What manufacturing tolerance do the black housings of the jumper cables have?
What lengths exist for the black housings?
Are there different cable diameters?
How big should the lug on the cover be?
Which material should be used?

The measurements (with a digital caliper) from different manufacturers of the jumper cables showed that there were hardly any deviations. The biggest deviation was the length from 12 mm to 14mm. Since most of them have a length of 14 mm, this measurement was also used for my CAD design.

The goal was to design a quick connector, i.e. put the cable in, press the lid on and it’s done. With this I wanted to avoid screws, cable ties, hose clamps, gluing or soldering.

Material and Dimensioning

To achieve this, I decided to use retaining lugs or claws. For this you have to pay attention to the dimensioning and the choice of the material. Probably the best material would be nylon. Unfortunately I don’t have the possibilities to print with nylon. This would have required a closed construction space. The same goes for ABS the second best solution. That leaves only PET or PLA. I still had a larger supply of colorless PLA, so I decided to use PLA. Note at this point: The color additive in the filament influences the printing properties and not insignificantly! For functional prints I always choose colorless PLA.

To be able to put 4 jumper cables into the case, I chose an inner dimension of 10.6 mm. For the side walls I chose a thickness of 1.7 mm and for the bottom a thickness of 1.46 mm. The outer dimensions were 4 mm x 14 mm x 25 mm.

Lid construction

For the lid, the dimensions are identical to the housing, but with an addition for the protruding tabs with the lugs. The dimensions of the tabs are based on my previous experience. I decided to use a second pair of tabs because it increases the holding force and distributes the force better. Also, if one tab should break, the lid would still hold securely to the case.

The shape of the lug at the end of the tab (Detail A) is important, as the 3D printer will not print this exactly as designed on the CAD.

As shown in detail B, an elevation was constructed on the inside of the lid. This elevation helps to press the cables down slightly when the lid is pressed onto the housing. The cables are fixed in the housing and pull the housing towards the stopper (detail D). The additional tension secures the cable housing more precisely. This works because the pressing takes place behind the fastening in the housing and the cables have some distance to the bottom of the housing. However, the height of the pressure bar (detail B) must not be too large, otherwise the lugs of the tabs cannot click into place on the bottom of the housing.

The roundings on the cable seat (detail C) are used for easy insertion of the cables. The apertures or also called windows were originally intended for the opposite side of a connector as a holding point. However, I discarded this because the holding torque is more than sufficient. The rectangular apertures now help with orientation during assembly.

Assembly

The assembly is quick and easy. The first Dupont cable is placed from the front on one of the two side panels and the cable housing is pushed to the stop (detail D). Then hold the housing and pull on the cable to eliminate any gap between the crimp connection and the cable housing. Now press the cable into the cable guide on the connector housing. Do the same with cable number 2, 3 and 4 and then press the cover onto the housing until it clicks.

Applications for the Dupont connector

Originally I had constructed this connector design for a project with many 4PIN RGB strips. After a short time I realized how practical the design was. I can use it for the Arduino, sensors, LED strips, Raspberry Pi and much more and that without soldering or using other tools. Of course, I know that you always have to leave a gap of 2 PINs between the connectors on the Arduino, but this doesn’t really bother me in everyday life.

Advantages of the Dupont connector:

Quick assembly
Universal use
Enormous holding force
Easy to print

Disadvantages of the Dupont connector:

Greater space requirement

Download files

The post 3D printed Dupont connector for jumper cable appeared first on Nerd Corner.

Printed connector as soldering aid for jumper cables and LED strips

Nerds — Tue, 26 Apr 2022 18:31:53 +0000

For one project, I spent a lot of time preparing cables (cutting, stripping, twisting, and applying solder to the strands). For prototypes, on the other hand, I usually prefer jumper cables. I have often thought that it would be incredibly practical to use jumper cables in the final product as well.

That’s why I designed a quick connector in CAD that makes it very easy to solder jumper cables. The connector serves as an ideal soldering aid. Of course, the wire diameter must be sufficient for the required number of amperes! On the market there are mainly inferior connectors. My STL file on the other hand is cheap and works perfectly.

This might also be interesting: Universal connector housing!

List of components

4 Pin RGB LED Strip
Jumper cable
Heat shrink tubing
Hot Glue

Project application

For a larger project I needed 16 RGB strips with 21 LEDs each. The strips were pushed into a 3D printed socket afterwards. The LED strip was separated directly at the pre-marked point with a standard pair of scissors (usually the RGB strips are divisible after every third LED).

For the jumper cables I chose one side male and the other female. The side with the PINs (male) were soldered to the RGB strip and the socket (female) was used as a plug. It is crucial to use jumper cables with square housing (standard dimension: 2.54 mm). The length of the plastic housing does not matter. Depending on the brand, the plastic housings are 12 mm or 14 mm long.

Procedure

Since no preparatory work on the cables is necessary, soldering can be started directly. I prefer to apply solder to the RGB strip at the soldering points (copper layer) first. After that I solder the PINs to the soldering points without additional solder. The PINs should not be soldered too deep towards the LED and the alignment must fit.

Then the connector comes into play. This connector is on the RGB side and open at the top. The RGB strip is inserted into the connector so that the solder joints are in the connector. Then the four cables are pressed into the slots and the solder joints are sealed with hot glue if necessary. For safety reasons, I recommend to attach a heat shrink tubing. This way you get a super strong connection!

Steps in pictures

Advantages:

No cable preparation
Strong connection
Easy 3D printing

Disadvantages:

Requires more space
STL file only for RGB strips with 10 mm width

Download files

- STL file of the soldering aid

The post Printed connector as soldering aid for jumper cables and LED strips appeared first on Nerd Corner.

Improved LM2587S voltage converter (Step-Up Modul DC-DC)

Nerds — Mon, 27 Sep 2021 21:26:22 +0000

I found some more possibilities to use the LM2587S voltage converter (step-up DC-DC module) after the development of the first case. The module is extremely useful to quickly supply other devices with voltage. Originally, I just wanted to use it to charge a vacuum cleaner battery and had to set the correct volts once for that.

However, it is impractical to vary the voltages for different devices. First, the input jack is located at the bottom of the case, which unfortunately creates an uncomfortable angle for holding the screwdriver when adjusting the voltage and leaves little room for your fingers. Second, a multimeter is needed each time to measure the voltage. The goal of the adjustments was to improve the handling and the design.

This might also be interesting for you: Development of a charging device from a LM2587S Step-Up

Liste der Bauteile:

1x hollow plug 5.5 x 2.1
1x screw socket 5.5 x 2.1
2x flat head screw M2x6
2x flat head screw M2x4
4x raised countersunk head screw M2x10
1x Module LM2587S DC-DC Step Up
2x Pico fuse 3A 125V / 230V
1x Mini Voltmeter Digital with LED display 0,36″ (optional)

Housing construction of the LM2587S voltage converter

The vertical position of the socket results from the housing length. Since the power input is now to be on the back, the housing had to be longer. 12 mm was sufficient to install the socket horizontally. Due to the length of the housing, the screwdriver can easily fasten the socket on the inside.

Alternatively, the socket could have been rotated 90°, which would have kept the socket on the side and the length of the housing the same. However, the distance to the opposite wall would be extremely small and problems would arise when screwing. You would need an angled screwdriver or drill mounting holes in the side panel.

Now the bridge bushings had to be modified. Otherwise the bridge would collide with the corner at the ends. The interfering parts on the bridge were removed in CAD. The column height remains the same, since the bottom thickness and the back wall thickness are the same. The lid also had to be adapted to the length and given a cutout or socket for the mini voltmeter.

The voltmeter 3631AS-1

When selecting the mini voltmeter, I chose the “3631AS-1” variant. This voltmeter sits on a circuit board that has tabs with holes so that you can screw it to the housing cover. On this voltmeter the cables are already soldered with the correct colors (red for plus and black for minus). To protect the voltmeter from mechanical damage, I added a frame to the case lid.

The case height does not have to be changed for the LM2587S voltage converter, because there was already enough space in the previous version. The work on the CAD is definitely an advantage here, because the lid can be extended easily without a cutout for the voltmeter and you get a variant “long” for those who do not need a voltmeter, but want to have the input at the back.

As always, the components were produced on the 3D printer and afterwards the thread was cut (in this case M2). Soldering is very simple, like with the predecessor, and the two additional cables from the voltmeter are screwed to the OUT cables on the hollow connector according to the color.

Setting and adjustment of the LM2578S voltage converter

Now to the adjustment of the LM2587S voltage transformer. Here was mainly the accuracy of the voltmeter interesting. Generally the adjustment should be done under load. That means with a connected load (e.g. a resistor). I repeated the measurements several times and was amazed about the accuracy of the mini voltmeter.

The maximum deviation was less than 0.04 V and this even with different input voltages. The device has been extensively tested from 4 V to 32 V. I recommend not using more than 30V output voltage for operation during longer operation, because the voltmeter is not suitable for higher voltages on a long-term basis.

Of course, the contact resistance is important, because each additional connector reduces the voltage. Therefore follows:

Avoid unnecessary plug connections
Always measure voltage at the last connection

Safety aspect

The safety should not be forgotten either, since the step-up in contrast to the step-down has an open circuit, it should be provided with a fuse! At my step-up I have subsequently attached (unfortunately not visible in the photos) a lazy pico fuse with 3A at the positive terminal on both the input voltage and the output voltage. Thus, you can start using it!

Download files:

The post Improved LM2587S voltage converter (Step-Up Modul DC-DC) appeared first on Nerd Corner.

housing Archives - Nerd Corner

DIY keypad lock – 3D printing and code

Construction of the housing

What will be inside the housing?

Keypad lock Housing design

Mounting and fastening

The support plate – the central mounting element

Fastening the components to the carrier plate

The LED cover and its attachment

Mounting the LEDs

3D printing of the components

Post-processing of the components

Soldering the components

Assembling the keypad lock

Mounting the keypad on the support plate

Wiring the keypad to the Arduino Nano R3

Assembling the carrier plate and housing

Connecting the cables and completing the power supply

Arduino code

Function

Door mounting

Locking Mechanism

Files for Download

Mini Digital Voltmeter

List of components

Construction

3D print of the first variant

Soldering and wiring the first variant

Construction of the second variant

Soldering and screwing the second variant

Function test

Files to download

Dupont Connector V1.1

Implementation of the Dupont connector

Assembling the Dupont connector

Files to download

Using a barrel jack as a switch

List of components

Assembly instructions for bracket and bridge

Wiring and soldering the barrel jack

Assembly and connection

Integration of the second power source

Files for Downloading

3D Printed Tealight Holder

List of components

Procedure

Power supply

Assembly

Files for download

DIY powerbank with voltage regulator and voltmeter

List of components:

Implementation

Construction

Step by step assembly

Download Files

Glare free lamp and powerbank

List of components

Choice of LED

Construction of the cover and middle cover

Assembly

Soldering the parts to the jumper cables:

Cutting and gluing the LED strips: The LED strip is separated into two times 6 LEDs and once 5 LEDs and glued to the intermediate cover. The cable opening on the lid for the plug must remain free:

Attach the hollow bushing to the intermediate cover:

Screw the battery shield into the housing after the ten threads have been previously cut into the housing.

Press the rocker switch into the cover:

Press LiPo 18650 into the receptacle

Connect cable and turn on:

If all LEDs light up, place the middle cover on the housing and then place the cover on the middle cover and screw it down:

Glare free lamp CAD design

Further notes

Download files

3D printed Dupont connector for jumper cable

List of components:

CAD design for Dupont connector

Material and Dimensioning

Lid construction

Assembly

Applications for the Dupont connector

Advantages of the Dupont connector:

Disadvantages of the Dupont connector: