A police-themed Pinewood Derby family build, brought to life with flashing lights, a two-tone siren, motion sensing, and a Home Assistant dashboard that moves with the car.
Project reference v1.1 · Updated October 13, 2026
UNIT 67 · LIFESAVERChange the tilt and switch between awake and sleeping. This browser demo uses illustrative readings; it does not connect to the car.
The car illustration follows pitch and roll. The status badge turns green within ±2°, amber up to 5°, and red beyond that.
Sleep pauses the flashing lights and marks the readouts as unavailable. No audio plays in this demo.
Hardware identified from the build owner and supplied ESPHome configuration.
The tiny main controller handles Wi-Fi, ESPHome, light switching, PWM siren tones, and the connection to Home Assistant. The board also includes lithium-battery charging support.
Seeed board documentation ↗BLE is a board capability; this project configuration uses Wi-Fi.
Acceleration is sampled every 200 ms over I²C at address 0x68. The firmware projects the readings into the car’s own axes to calculate front/back and left/right tilt.
The dashboard also exposes the MPU’s internal temperature, which is a sensor-chip reading rather than an ambient thermometer.
A compact rechargeable lithium-polymer battery powers the car’s electronics. The battery set shown for this build includes two 650 mAh packs with Molex 2.0 connectors and two USB charging leads.
The controller runs the alternating police lights and adjustable two-tone siren, while battery monitoring keeps the charge status visible in Home Assistant.
A 200 ms interval toggles GPIO9/10 and GPIO3/2. Each pair has an interlock and a 200 ms changeover delay. The dashboard adds red/blue reflections around the illustrated car.
GPIO8 alternates between configurable low and high frequencies. Defaults are 850 and 950 Hz; each tone adjusts from 100–3000 Hz. Volume is a 0–100% PWM setting, with a master siren enable.
Capture flat, front-lift, and side-lift positions, solve the car axes, then zero the level reading. Solved axes and zero offsets are saved across restarts.
Moving averages smooth the acceleration and angle readings. A 0.3° deadband reduces jitter near zero; the car-level sensor is true when both tilt angles are within ±2°.
The 3.7 V, 650 mAh LiPo battery has two firmware readings: Battery Voltage in volts and Battery Level as an estimated percentage. Voltage is measured through XIAO D2/A2 (GPIO4); percentage is calculated from that same reading, with no second pin.
The car publishes active at boot and inactive one second before deep sleep. Adjustable defaults are 30 seconds awake and 30 minutes asleep. A motion-sensitivity setting and GPIO5 wake input are configured.
Sleep duration and motion sensitivity are applied during boot in the supplied reference. Verify the MPU interrupt connection and wake behavior on the assembled car; physical operation has not been tested here.
These are raw GPIO numbers in the supplied YAML, not XIAO D-pin labels. The supplied firmware still selects esp32-c3-devkitm-1; the physical board is the XIAO confirmed by the owner.
| Function | ESPHome GPIO | XIAO pin |
|---|---|---|
| Battery Voltage (ADC1) | GPIO4 | D2 / A2 |
| Battery Level (%) | Calculated from voltage | No additional pin |
| MPU6050 SDA / SCL · 0x68 | GPIO6 / GPIO7 | D4 / D5 |
| Configured wake input | GPIO5 | D3 |
| Light output pair A | GPIO9 / GPIO10 | D9 / D10 |
| Light output pair B | GPIO3 / GPIO2 | D1 / D0 |
| Siren PWM | GPIO8 | D8 |
Keep all three captures in the same awake session. Lift captures are temporary and are lost when the controller restarts.
The original SketchUp view and Home Assistant card supplied for this project.
Public reference files with private credentials removed. The supplied firmware logic is preserved; it has not been compiled or tested on hardware.
Setup & Entity Mapping Guide · v1.1
Schematic & Wiring Guide · v1.1The card includes matching vector artwork, explicit unavailable-data handling, and a visible sleeping state. Install custom:button-card, copy the graphics to /config/www/pinewood/, and map the entities to your own Home Assistant installation.
Firmware API, OTA, Wi-Fi, and fallback hotspot credentials use local !secret references. Supply your own values privately.
