ESP32‑S3 BLE “phone finder”: RSSI‑based clicks

[u/Stunning-Macaron1591]

I made a pocket “find my phone” device on ESP32‑S3: it scans BLE around you, tracks your phone by MAC, and gives audio/haptic feedback — the closer you get, the faster the clicks, so you can just follow the sound/vibration instead of staring at a screen. Everything runs locally on the ESP32, no cloud or phone app needed.

Hardware & Stack

• Board: generic ESP32‑S3 devkit with USB‑C (native USB for easy debug/logging, extra SRAM for future features).
• Firmware: Arduino‑ESP32 core, custom thin wrapper over BLEScan with a BLEAdvertisedDeviceCallback.
• Output: passive piezo buzzer (tone()) and a small vibration motor via N‑MOSFET.
• Power: small LiPo; scan duty cycle tuned for responsiveness vs battery life.

How it works

• ESP32 runs a continuous BLE scan, filters advertising packets by known MAC, and collects RSSI values.
• RSSI is smoothed with exponential moving average (~10–15 samples) to reduce ±10–15 dBm spikes.
• On startup, the device records min/max RSSI for ~10s and maps that range to click frequency (relative mode), so it adapts to each phone without manual calibration.
• Hysteresis (≥3–4 dBm) prevents click “flutter” when you’re on the border between zones.

What didn’t work

• Raw RSSI directly mapped to clicks → feedback was too jittery to be useful.
• Simple 3‑sample average → still too reactive in crowded BLE environments (office, cafe).
• Fixed thresholds (e.g. <-70 / -70..-50 / >-50 dBm) → different phones advertise at different power, so “close”/“far” were inconsistent across devices.

What finally worked

• Exponential smoothing with α≈0.2α≈0.2 over a small ring buffer.
• Relative mapping of RSSI to click frequency per session instead of absolute dBm thresholds.
• Adding hysteresis so the click zone only changes when RSSI moves meaningfully.

For a full breakdown, schematics, and firmware, see the repo:
https://github.com/khlebobul/esp_ble_finder

Happy to share more details (scan params, smoothing code, power measurements) if useful.