The LambdaKB LK7D is a simple 7 keys hotswap macropad with per-key RGB LEDs and an OLED display. The goal was to create a simple macropad based on the XIAO RP2040 microcontroller that had all the bells and whispers of a modern keyboard.
This was created as an experiment to learn more about designing PCBs and to have a simple and cheap way to test new features (such as integrating OLED displays and RGB LEDs in QMK / Vial).
| Front | Back |
|---|---|
The PCB has been designed in KiCad EDA 9.0 using the kicad-lkbd libraries.
You can preview the project files using KiCanvas directly in your browser and download the latest fabrication files for JLCPCB from the latest release.
The exported schematic is also available under output/schematics.
| Parameters | Value |
|---|---|
| Base Material | FR4 |
| Layers | 2 |
| Dimensions | 57.15 × 57.15 mm |
| PCB Thickness | 1.6 mm |
| PCB Color 1 | Black |
| Silkscreen | White |
| Surface Finish 2 | Lead Free HASL or ENIG |
| Copper Weight | 1 oz |
| Via Covering | Tented |
| Min Via Hole Size | 0.3 mm |
| Board Outline Tolerance | ± 0.2 mm |
| Part | Ref. | Quantity | Optional | Remarks |
|---|---|---|---|---|
| PCB | LK7D PCB | 1 | ❌ | The PCB itself. |
| XIAO RP2040 Controller | SeeedStudio XIAO RP2040 | 1 | ❌ | Main controller for QMK/Vial. |
| 1N418 Diodes | 1N4148W T4 SOD-323 | 7 | ❌ | Switch matrix diodes. One MUST be installed under the encoder. |
| Kailh Hot-Swap Sockets | CPG151101S11-16 | 6 | ❌ | MX style hot-swap sockets. |
| Key Switches | Any Cherry MX Compatible Switch | 6 | ❌ | MX style switches. |
| Rotary Encoder | Any EC11 / EC12 style 5-pin Encoder | 1 | ❌ | Can be installed either in top left or top right of the PCB. Only one per PCB is supported. |
| 100nF Capacitor | 1206 SMD Ceramic Capacitor | 2-3 | ✅ | Both C1 and C2 should be installed if populated, used for noise filtering of encoder readings. C3 is only required if a Logic Level Shifter is installed. |
| 0.91" OLED Display | SSD1306 0.91" 128X32 OLED I²C Display Module | 1 | ✅ | Optional, occupies the place of the non-populated encoder and sits on top of the XIAO MCU. |
| RGB LEDs | SK6812MINI-E | 6 | ✅ | Optional, RGB LEDs can be installed under each key switch. |
| 5V Logic Level Converter | SN74AHCT1G125DBVR or SN74LV1T125DBVR (SOT-23-5) | 1 | ✅ | Optional, required if your RGB LEDs are not 3.3V logic tolerant. You MUST cut the JP1 jumper if populated. |
Coming soon.
The pre-build firmware available in this repository are compiled using Vial (a fork of QMK allowing customization via a GUI).
As per the original license of both Vial and QMK, the firmware itself is licensed under the GPLv3 license and its source code is available at vial-qmk/keyboards/lambdakb/lk7d.
| Layer 0 | Layer 1 | Layer 2 | Layer 3 |
|---|---|---|---|
Layer 4, 5 and 6 contains similar layouts with macro keys going from M15 to M29.
| Encoder Position: Left | Encoder Position: Right |
|---|---|
This design is licensed under the CERN Open Hardware Licence Version 2 – Strongly Reciprocal (CERN-OHL-S-2.0).
You are free to use, modify, and distribute this design for any purpose, provided that:
- Attribution: Appropriate credit is given, a link to the license is provided, and any modifications are clearly indicated.
- Reciprocity: Any derivative works must be released under the same license.
If you are a retailer or business interested in producing or selling this design or related products, I’d love to discuss it! Please feel free to reach out so we can explore potential arrangements.
Footnotes
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You can select any PCB color you want but some manufacturers such as JLCPCB may charge you more for uncommon combos (such as Blue PCB + ENIG Surface Finish). ↩
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The "HASL (with lead)" option is extremely discouraged due to the risk of lead poisoning. We strongly recommend paying the premium for the "Lead Free HASL" option. ↩