A track-call limiter for slot car racing, built on the RP2040-based Pimoroni Tiny 2040 using the Raspberry Pi Pico C/C++ SDK. When a car comes off the track, the driver needs the track de-energized to safely reset it — TrackCall gives each player exactly 3 of these calls per race, then locks them out.
IMG_3545.MOV
Pressing the Track Call button de-energizes the track for one second (so the player can put their car back on) and lights a different LED to show how many calls have been used. Once the 3rd call is used, the track can no longer be de-energized — pressing the button again just flashes all three LEDs to tell the player they're out of chances. The Reset button clears the call count back to zero for the next race/heat.
| Call # | LED | Track Power (Relay) |
|---|---|---|
| 0 (ready) | Green | energized |
| 1st call | Yellow | de-energized for 1s |
| 2nd call | Red | de-energized for 1s |
| 3rd call | all off | de-energized for 1s |
| 4th+ attempt | all 3 LEDs flash once | stays energized — call denied |
Inputs are debounced with a 50ms settle read, and the main loop runs on a 250ms cycle.
Built and wired against the schematic below.
| Component | GPIO |
|---|---|
| Track Call button | 2 |
| Green LED | 3 |
| Yellow LED | 4 |
| Red LED | 5 |
| Relay | 6 |
| Reset button | 7 |
Requirements: Raspberry Pi Pico C/C++ SDK, CMake, and an ARM GCC embedded toolchain (arm-none-eabi-gcc).
Easiest path: open this repo in VS Code with the Raspberry Pi Pico extension installed, then run Compile Project from its sidebar — it handles the SDK, toolchain, and build for you.
Manual build:
git clone https://github.com/olael94/TrackCall.git
cd TrackCall
mkdir build && cd build
cmake ..
makeTo flash: hold BOOTSEL on the Tiny 2040 while plugging it into USB, then drag build/TrackCall.uf2 onto the drive that appears.
TrackCall.c — state machine + GPIO logic
CMakeLists.txt — build configuration
pico_sdk_import.cmake — pulls in the Pico SDK
TrackCallZeroSchematic-1.png — circuit schematic