I like numeric keypads. They come in handy when I am working with CAD packages and stuff. So you can see this as a piece of quiet rebellion against the world of hipster 40% or 60% fancy keyboards but one that still gives you a durable, fancy, interesting, artisanal, hand-crafted, mechanically-keyed product at the end of it.
This is partially developed using Ruiqi Mao's Keyboard PCB guide as a reference... except that I'd suggest you don't actually use that guide as a reference because it's got some inaccuracies and at this point is old and unmaintained. It turns out that, because I was designing it around parts that I already was comfortable with using and based it off of prior designs, I'd managed to sidestep all of the problems. The current hotness is arguably the ai03 Keyboard PCB guide which seems to be newer and more accurate.
Otherwise, this has design lineage through a few earlier designs I cooked up but won't bother posting because they were mostly design experiments and aren't really useful for anyone.
- Be mostly standard in being designed for the QMK firmware, use Cherry MX keyswitches and standard-sized keycaps, etc.
- Contain the 17 keys of a numeric keypad, plus maybe some encoders for the funs.
- Look vaguely interesting as just a PCB.
- Use parts I already had in my parts bin for other projects.
- 17 keys in the standard layout so you can use pretty much any standard-layout numeric keypad caps.
- 2 rotary encoders with push-buttons.
- ATMega32u4 processor
- MicroUSB port
- Extra ESD protection diodes and a polyfuse for durability
- Programming port that you shouldn't actually need to ever use.
- 9 4-pin SK6812 "NeoPixel" RGB LEDs pointed downward for underglow
- 6 M2.5 mounting holes
- Not quite able to fit in the 10cm x 10cm box because of the size of the keys.
- Puns on the silkscreen
I did a bunch of digging and datasheet reading.
Given that I'm plugging this into the USB port on my computer, I tend to go for safety. Thus, there's a ESD diode to protect the USB lines from spikes, there's a polyfuse on the power line so it won't use too much power, there's the required capacitors, and there's a decoupling network to keep the EMI from the cable sheath from crossing over to the ground plane. This is more than most of the development boards.
I also added a polyfuse in case you short power to ground so it will reduce the chances that things go really bad.
Col: PF0, PD4, PD5, PD3, PD2 Row: PB6, PC7, PC6. PB5, PB4 Encoders: PF5/PF6, PF1/PF4 Col -> Row
Neopixel: PB7
| Reference | Quantity | Value | Footprint |
|---|---|---|---|
| C10 | 1 | 4.7 nF | 0805 |
| C1,C2 | 2 | 22 pF | 0805 |
| C3 | 1 | 10 uF | 0805 |
| C4 | 1 | 1 uF | 0805 |
| C5,C6,C7,C8 | 4 | 0.1 uF | 0805 |
| D1,D2,D3,D4,D5,D6,D7,D9,D10,D11,D12,D13,D14,D15,D16,D17,D18,D27,D28 | 19 1N4148 | SOD123 / Axial | |
| D19,D20,D21,D22,D23,D24,D25,D26,D29 | 9 | SK6812 | 5050 PLCC4 |
| D8 | 1 | PRTR5V0U2X_215 | TO-253-4 |
| F1 | 1 | 500 mA Polyfuse | 1206 |
| H1-H6 | 6 | Mounting Hole | M2.5 |
| J1 | 1 | MicroUSB | Amphenol 10103594-0001LF |
| J2 | 1 | AVR-ISP-6 | 2x03 2.54mm pitch vertical SMD |
| MX1,MX2,MX3,MX4,MX5,MX6,MX7,MX9,MX10,MX11,MX12,MX13,MX14,MX17 | 14 | Cherry MX | 1U |
| MX8 MX15 | 2 | Cherry MX | 2U Vertical |
| MX16 | 1 | Cherry MX | 2U Horizontal |
| R1 | 1 | 1M | 0805 |
| R2,R3 | 2 | 22 | 0805 |
| R4,R5 | 2 | 10k | 0805 |
| R7 | 1 | 1 M | 0805 |
| S1 | 1 | Toggle switch | RS-187R05A2-DS MT RT |
| SW1,SW2 | 2 | Rotary_Encoder_Switch | PEC11R-4215F-S0024-0-0-0 |
| U1 | 1 | ATMEGA32U4 | TQFP-44 |
| Y1 | 1 | 16 MHz | HC49-U |
The gerber files are as I upload to JLCPCB to be fabbed.
If other people start wanting to try and fab this board, I'll write an actual proper assembly guide. :)
Either way, the important points to consider are:
- Everything should be solderable with a regular old temperature-controlled ESD-protected soldering iron.
- You don't need to populate J2 unless you get yourself in deep trouble.
- The keyboard diodes are hybrid footprints that can use either a SOD-123 surface mount diode or an axial one. I actually find SOD-123's easier to solder all told but I'm probably at least a bit odd.
- You can use either PCB-mount or plate-mount keyswitches and there are holes for PCB-mounted stabilizers.
- You can use a set of Mill-Max 7305-0-15-15-47-27-10-0 maybe the new 3305-1-15-15-47-27-10-0 receptacle connectors so that the keyswitches can be hot-swapped -- The 3305-X series is a new part specifically designed for keyswitches.
You should just be able to program a freshly constructed board to the USB port and use the QMK programming tool to put an appropriate firmware on the board with the default bootloader.
I need to actually submit the upstream patches for QMK.
There are 6 M2.5 sized mounting holes in semi-convenient locations.
This will appear later, still working on it!
- I might try to trim a few mm off of each of the edges.
- I used an Amphenol 10103594-0001LF connector for Micro USB. They are better than a lot of the Micro USB connectors but there's some nice USB-C connectors that look even a little bit sturdier out there these days.
- I used a 5.2mm tactile switch that was from all of the designs I was making around this point in time. These days, I'd probably use a reset button that's smaller yet actually a bit nicer.
- I might remove the hybrid SOD123/Axial feature because I actually solder SOD123's faster than I solder axial parts these days.
- I might throw in a num-lock LED and maybe a few NeoPixels on the top side for more light funs.
- The programming port is kinda annoying in the layout and I guess I need to look at more alternatives in the rare case you need to bootloader it.
