Today I am going to build a Raspberry Pi Pico-based number pad. I am going to build a simple ortho linear number pad with 20 switches. Then I am going to go through how I installed KMK firmware on it.
KMK can be installed on python based microcontrollers. It can be used for things as simple as number pads all the way up to full keyboards.
To build this num pad I needed the below supplies. Please keep in mind these will change depending on if what you build is larger or smaller.
None of the links below are affiliate links
- (1) Raspberry Pi Pico
- (20) Key Switches
- (20) Diodes
- (20) Key Caps
- Case and hardware
- 3D printer (For the case)
- Wire cutters
- Sand Paper (optional)
- Soldering Iron
- USB cord
Step 1: Prepare the Case
I designed and printed this case out of PLA on my Ender 3 Pro.
The case was designed to use up to 6 M3 screws, but for the num pad, I will only be using 4 of them.
The edges came out a bit rough so I screwed the base onto the top and wet sanded the edges to smooth them out. In just a few minutes I was able to get rid of the bumps and gave the case a nice matte finish.
Step 2: Install the Hardware Components
I am going to lump all the hardware into one step. As I mention in the Part 1 video I have some advice here so you can, hopefully, have an easier time than me.
I have included the circuit diagram above.
- Install the switches
- Put all the switches in the same direction. This makes it easier to install the diodes in the next step.
- Bend the diodes
- Bend one leg of the diode over so that it makes a 45-degree angle from the rest of the diode. Set this angle over the pin so the diode runs down the side of the switch
- Bend the other leg at 90 degrees. This can then be used to connect to the rest of the row of diodes
- Take a look at the other diagram in this step for a better idea of what I mean.
- Install the diodes
- Place the diode in place and then solder the diode to the switch first
- Solder the 90-degree leg to the rest of the row of diodes
- Double-check the diode orientation every time, the orientation doesn’t matter it just matters that they are all the same
- Trim the excess leadoff
- Connect the columns
- I used a piece of the solid core wire and cut the insulation every 14ish mm and then you can slide the insulation around to make small gaps for the other pin on the switch.
- I also remove about 1” (25mm) of insulation from one end to make enough space to move the insulation around
- When putting the wire in place, I zigzag between the pins to connect. This helps hold it in place while I solder
- Trim off the excess wire
- Connect the rows and columns to the Pico
- I used some long sections of stranded wire to connect to each row and column
- Then connect them to the Pico. The pin numbers are not super import just keep track of them so they can be used in the code later.
Step 3: What Is KMK?
Really quickly I am going to touch on what is KMK and why am I using it.
“KMK is a feature-rich and beginner-friendly firmware for computer keyboards written and configured in CircuitPython.”
Here is a link to their GitHub with more information.
I am using it because I find it much easier to use than QMK, the standard for most keyboards. It can all be done in plain text on any computer and is in python, which I know.
I’m making this instructable and the videos linked because I want more eyes on this project because I think it’s great, and I’m not good enough at python to help build software so I hope someone who does this can help with this project.
Step 4: Install the Software on the Pico
With all the hardware in place, we need to install some software on the Pico.
This can all be done without installing any other software.
I learned how to do all of this from the KMK GitHub Getting Started page. There is tons of good information there if you want more information or features.
The first piece of software needed is the most recent CircutPython UF2 from Adafruit.
Simply download the file
Hold the boot button down on the Pico and plug it into the computer (if it keeps giving you an error, try plugging it in without holding down the boot button)
The Pico should show up as an external storage device
Drag the downloaded UF2 file to the Pico. On its own, it should eject and then after a few minutes reconnect with a new name
The next thing is the KMK firmware “install”.
Grab the latest version of KMK from their GitHub (get this link from the getting started page).
It will download a .zip file. Extract all the files.
In the folder find the KMK folder and the boot.py file.
Copy those items from the folder and paste them in the Pico
That should be all the setup on the Pico
Step 5: Add a Code.py
So far the stage has just been set for KMK now I need to tell it what to actually do.
This is done using a code.py file. There should be one on the Pico, if not just create a new file called code.py.
Luckily most of the hardworking has been done already. I just need to copy the example code from the GitHub page and paste it into the code.py file. I edit this file using NotePad++ but this can also be done in NotePad
I need to give this file all the specifics of my num pad.
To do this I first need to give the code the pin numbers for the rows and columns in lines 11 and 12.
Next, I need to change the diode orientation as the code needs to know how everything is set up. I changed it from COL2ROW to ROW2COL.
Most of the way done now, I just need to add the keymap. Or what keys should be where? I referenced this web page to find all the keycodes I can use. I won’t go over this in detail but take a look and what I used and make any changes you want.
print("Starting") import board from kmk.kmk_keyboard import KMKKeyboard from kmk.keys import KC from kmk.matrix import DiodeOrientation keyboard = KMKKeyboard() keyboard.col_pins = (board.GP0,board.GP1, board.GP2, board.GP3) # try D5 on Feather, keeboar keyboard.row_pins = (board.GP4, board.GP5, board.GP6, board.GP7, board.GP8) # try D6 on Feather, keeboar keyboard.diode_orientation = DiodeOrientation.ROW2COL keyboard.keymap = [ [KC.A, KC.LSHIFT, KC.TAB, KC.KP_PLUS, KC.N7, KC.N8, KC.N9, KC.KP_ASTERISK, KC.N4, KC.N5, KC.N6, KC.KP_MINUS, KC.N1, KC.N2, KC.N3, KC.KP_SLASH, KC.BSPC, KC.N0, KC.KP_DOT, KC.KP_ENTER, ] ] if __name__ == '__main__': keyboard.go()