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: <Keypad.h> for the keypad, <Adafruit_NeoPixel.h> for the WS2812B LEDs and <Servo.h> 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 <Keypad.h>
#include <Adafruit_NeoPixel.h>
#include <Servo.h>
//========================================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.

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:

1. Push the cables into the socket strip.
2. 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).
3. 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).
4. As soon as the DuPont plugs are fixed in the housing, the cover is fitted and snapped into place (Fig. 3.0.3).
5. 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.

I do a lot of screwing in my workshop and most often I use Torx, hexagon socket and Phillips bits. I always buy these bits in packs of 10 or 25 because they are cheaper and I like to have a small stock. I feel the same way about tools, so I decided to design a few bit adapters and 3D print them.

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

Procedure

The first thing I did was to tidy up my socket cases to find out which adapters are actually needed. The most common square sizes for sockets are:

• ¼” equals 6,35 mm
• 3/8″ equals 9,52 mm
• ½” equals 12,7 mm

In picture 2.0 I have put together some square photographs. Figure 2.0.1 shows a ¼” hexagonal shaft with three different square sizes. This hexagonal shaft can be easily clamped in a three-jaw chuck which is usually used with a drill or cordless screwdriver. Picture 2.0.2 shows the version with a handle, where the square is at the end of the shaft. In 2.0.3 you can see three joints with different square sizes and picture 2.0.4 shows a so-called “spring pressure piece”. The resilient thrust piece has the task of retracting when inserted into the counterpart and engaging in the intended notch or groove in the counterpart in the final position. This ensures a better hold of both parts in the connection. I have marked the position of the springy pressure piece on the square with red circles on some of the squares as an example. It is important for me to explain the function, because in the construction of the adapter a different solution is realised.

CAD construction of the bit adapter

The realisation on the CAD is actually quite quick. The dimensions for the depth of the square on one side and the insertion depth of the hexagon on the other side of the adapter are measured on the shafts. Picture 3.0.1 shows the surface (red) on the square that is pushed into the adapter, which is the same as the surface on the hexagon (black) in picture 3.0.2. In picture 3.0.3 I made a cut and marked the cut surface in green. The placement of the two shafts is shown by the colours.

Only the square dimensions are decisive for the outer dimensions of the adapters. Since the square shafts are getting bigger and bigger, the outer diameter of the adapter must of course also be adapted. I have therefore added a step to the ½” adapter (4.0.3). After all, there is enough material in the hexagon as it does not change. The recesses or pockets on the lateral surfaces are not for show. On the one hand they serve the stability of the adapter and on the other hand they save material. The two threads are the same on all adapters. The M3 threads are used for optional clamping of the shafts.

I use studs with a hexagon socket, which are flat at the end in order not to damage the surface of the shafts. You can also use normal screws if they don’t bother you. The position of the threads can be seen in the sectional view in figure 3.0.3.

Excursus on spring-loaded pressure pieces: The spring pressure pieces have already been mentioned in picture 2.0.4. I have been trying to use them in plastic for several years and have always found that they do not work. It is easier to design the clamping with screws and it is guaranteed to work!

Finally, the bit adapters are printed and cleaned and the M3 threads are cut. In the pictures under 5.0 you can see some examples for the use of the adapters.

Note

The bit adapters are of course only suitable for use under 15Nm. I easily reached this value with carbon fibre reinforced filament. With higher values there is a risk of breakage and therefore also a risk of injury!

Files for download

• Adapter 3/8″ to  ¼”

The post 3D printed bit adapter square / hexagon appeared first on Nerd Corner.

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.

To organise the workshop, I have developed a storage box for CR2032 and similar batteries of this type. There are already a few, but they all had the same shortcoming. The battery containers for CR2032 must always be opened with the proper side facing upwards, otherwise everything falls onto the floor. My battery cases for the CR2032 offer safe and clean storage without the cells falling out. In addition, you always have an overview of the number of batteries present.

The container is available in 2 versions, one for 10 and one for 22 button cells. The container consists of a drawer and a cover (container) and is safe against shocks and falls. The batteries are simply clicked into place and hold firmly in their drawer.

You might also be interested in: 3D printed Dupont connector

Construction of battery container CR2032

The container must be stable and durable, but still have handy dimensions. In addition, each individual battery must sit firmly in its compartment and yet be easy to remove. I also asked myself how many batteries the battery container for the 2032 should actually contain. Most sets consist of 5, 6, 8 or 10, sometimes even 20. In any case, the container had to fit in my desk drawer. As I was not sure about the number of batteries to be stored, I decided on two variants, one with 10 pieces and one with 22 pieces.

The construction on the CAD starts with the drawer, i.e. the slide-in part, the long part for 22 pieces. The width of the drawer depends of course on the width of the battery, the battery is 3mm thick, 2.95mm to be exact, and needs enough air between the individual walls. A gap of 0.15-0.2mm for each side is enough to avoid friction. So if we add it all up, we get a shaft width of 3.3-3.4mm. We create the holding force that prevents the battery from falling out of the shaft with the edge trick. We create a circular pocket in the centre of the slot with a larger diameter than the battery. Then we cut off about 1 to 3 mm of the material above the centre point, thus creating an edge. This edge must be slightly smaller in absolute length than the diameter of the battery (in this case smaller than 20mm). If you now push the battery into the shaft, it must overcome the edge, which is also possible due to the elasticity of the material.

Now the battery sits in the shaft and cannot overcome the edge in the other direction with its own weight. This principle is actually quite simple, with the necessary knowledge about material, manufacturing tolerances, forces and holding torques. In the end, it was a mixture of experience and a few test prints until the optimum result was achieved. Now the battery fits neatly into the shaft and holds perfectly. And with gentle pressure, the battery can also be removed from the shaft again.

The next goal was to design the slot so that it holds securely in the case. This is also an interaction of material elasticity and the right diameter at the collar that holds the construction together. After a few test pressings, I was satisfied.

The shell of the CR2032 battery container is quickly constructed. Basically, it is a cylinder with a base. The inner diameter was adapted to the insertion size to ensure locking and the hole in the bottom of the sleeve is for air release, because when the insertion is pushed into the sleeve, the air must be able to escape.

Files for download

• Battery container CR2032

The post 3D printed battery container for CR2032 appeared first on Nerd Corner.