jumper cable 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.

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.

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.