Hardware
What you need
| Part | Notes |
|---|---|
| Mini ESP32-C5 dev board | About US$6. Dual-band Wi-Fi 6 + BLE, native USB, single-core RISC-V. This is the timer. |
| USB-C cable | Power and the USB connection to a phone or computer. A power bank runs it at the gate. |
| Optional: Android phone | For the LapDog app. USB needs an OTG adapter. |
| Optional: HDZero goggles with ELRS Backpack | Shows lap times in your OSD over ESP-NOW. |
| Optional: RacePanel | Also receives the ESP-NOW lap messages. |
An ESP32-C5 board with a touchscreen makes a good test bench, and later a 5.8 GHz field scanner. The antennas differ, though, so signal levels you measure on one board won't match the mini board. Tune your thresholds on the board you'll actually use.
Video systems
- Analog and HDZero on any fixed channel: Raceband, Fatshark, Boscam E/A/B and Lowband.
- DJI and Walksnail aren't supported.
The board's buttons and light
- BOOT, long press (1 s): arm or disarm. BOOT is a strapping pin, so don't hold it while powering on.
- BOOT, short press while armed: start the next heat.
- LED: slow blink = idle, solid = armed, flicker = lap. It's easy to read with goggles half on.
Things to know
- Fixed gain is the big unknown. Wi-Fi automatic gain control would flatten the peak. Whether ESP-SDR's debug path allows fixed gain is still being tested.
- Indoor reflections. A 25 mW whoop indoors gives weak contrast between near and far. Low VTX power and a shielded or directional antenna on the timer help.
- Band edges. Sensitivity can drop near 5.9 GHz. Practise on mid-band channels.
- Fragility. ESP-SDR uses undocumented registers. A new ESP-IDF release or chip revision may break it.