Optical keyboard PCB based on Gateron MX optical switches (KiCad project).
Keyboard matrix uses column-to-row scanning approach. The IR (infra-red) led's in each column is connected to a GPIO pin configured as output. A column is powered by setting the pin HIGH. Each row is connected to a GPIO pin configured as input so that voltage drop across the load register of PT (Phototransistor) can be read.
QMK code is in a PR. In the
qmk tree you could find it in keyboards/opticalkb/rev1 folder.
This is not a high-performance keyboard since IR's are provided with very minimal current (way below the suggested operating value). This is done so as to keep the design simple. A single GPIO pin of STM32F4 (set as output) can provide 20 ma. Each IR is supplied with ~3.6 ma. The total current for 5 rows (IRs) falls within the allowable maximum current per pin. Yet it achieves a scan rate of 400 hz. Since there is no debounce delay the latency (before USB transit) is 2.5 ms. Compared to mechanical keyboards (with 5 ms debounce delay) this keyboard achieves respectable performance. It is possible to push scanning rate much higher, but it requires a different matrix design and additional switching components to increase current to IR.
Follow the blog for more keyboard designs in the future.
It takes minimal effort to put together this keyboard. When you order from jlcpcb have them assemble only 2 (out of 5) pcbs with SMD components (choose green FR4). The other pcb's can be used as base plates. The two pcb's (one with SMD assembly and one without) are soldered together using a special type of tin-coated standoff. If you are using a heatgun use solder paste generously. If using soldering iron solder from back of the standoff also. Then screw the switch plate on top. There is also a wrist rest. You can eliminate the wrist area completely by editing the Edge Cuts layer of main pcb. All pcb's are 1.6 mm thickness.
All the part numbers (of jlcpcb) are embedded in the symbols so you can generate BOM.
Switch plate is in switch-plate folder. Wrist support is in wrist-support folder.
- SMTSO-M2-3.5ET standoff (17 pcs)
- M2x4mm screws (17 pcs)
- Blackpill STM32F401 MCU
For wrist support:
- M2x4mm screws (8 pcs)
- SMTSO-M2-10ET standoff (8)
