A high-efficiency, battery-powered wind speed sensor (Anemometer) using the ESP32-C6. This project leverages the ULP (Ultra-Low Power) co-processor to monitor wind pulses while the main CPU is in Deep Sleep, allowing for years of battery life.
The project uses the LP/ULP core to count anemometer pulses while the main CPU stays in deep sleep, then wakes periodically to compute wind speed and advertise telemetry over BLE using BTHome v2 format.
- Ultra-Low Power: Can be as low as ~15µA in deep sleep on the ESP32-C6 alone. Actual current depends on the board and any attached hardware. The main cores only wake up to calculate and transmit data.
- BTHome V2 Protocol: Works natively with Home Assistant via Bluetooth—no custom integration or ESPHome YAML required. See bthome.io.
- Waterproof: Designed to be waterproof for outdoor use.
- Intelligent Reporting:
- Wind Detected: Typically reports on the next 5-second wake cycle while wind is present.
- Change Detection: Tries to report a speed change as soon as it is noticed on the next wake cycle.
- Heartbeat: Sends a periodic "still alive" update, usually about every 60 seconds during calm periods.
- Hardware Debouncing: ULP-based software sampling filters out mechanical reed switch "bounce."
If you are building a similar low-power sensor, these patterns are practical to reuse:
- Keep the main CPU in deep sleep and let the LP/ULP RISC-V core handle pulse counting.
- Wake on a fixed interval, compute pulse delta and wind speed, then advertise only when needed.
- Use BTHome v2 so the sensor works directly with Home Assistant over BLE.
- Add a heartbeat report so the device still publishes when conditions are calm.
- Filter reed-switch bounce in ULP software instead of relying only on hardware.
- Use RTC-capable GPIOs for ULP inputs on ESP32-C6, and avoid strapping pins.
- Add a capacitor across the battery sense divider to stabilize high-impedance ADC readings.
- Keep timing, calibration, BLE, and ADC values in a single header so they are easy to tune.
- Treat wind-speed calibration as a single empirical factor that can be adjusted without changing the rest of the flow.
- Preserve the PlatformIO + ESP-IDF setup and the debug/release sdkconfig defaults for repeatable builds.
- ESP32-C6 Board (e.g., ESP32-C6 Super Mini).
- For ESP32 and ESP32-S3 boards, check the ESP32/ESP32-S3 anemometer project.
- Anemometer (3-cup type with a Reed Switch).
- Battery: Li-ion 18650 or LiPo.
| Item | Quantity | Notes |
|---|---|---|
| ESP32-C6 Super Mini | 1 | Very cheap and low power board |
| 3D-printed anemometer | 1 | STL files for the 3D-printed parts |
| 608 bearing 8x22x7 mm | 1 | Very common bearing for shaft support |
| M3 heat-set insert | 3 | For connecting the main body to the support and collar |
| M3 hex socket cap screw M3x10 | 3 | Fastens the main body to the support |
| Reed switch | 1 | Wind pulse sensor |
| Magnet 6x3 mm | 2 | For triggering the reed switch |
| O-Ring 8x2 mm | 1 | To seal the base of the rotor and the support |
| Battery | 1 | Li-ion 18650 or LiPo |
| Battery Holder | 1 |
Connect the reed switch between SENSOR_GPIO pin and GND (no need of external pull-up resistor because internal pull-up resistor is used).
SENSOR_PIN
|
|
+ |
+--- Reed switch
+ |
|
|
GND
For battery monitoring, a 470 kΩ resistor divider is required. For stable ADC readings with high-value resistors, place a 0.1uF capacitor from ADC pin to GND.
BATTERY_ADC_GPIO
|
|
B+ -----/\/\/\/------+-----/\/\/\/-----+----- GND (B-)
470k | 470k |
| |
+-------||--------+
0.1uF
(optional)
- PlatformIO
- ESP-IDF framework via PlatformIO (already defined in
platformio.ini)
Advertising payload includes BTHome v2 service data with:
- Packet ID (object id
0x00) - Battery percentage (object id
0x01) - Wind speed in 0.01 m/s units (object id
0x44)
Device name in advertisement: Wind Sensor
Edit src/anemometer.h:
#define SENSOR_PIN 6 // GPIO used for the anemometer pulse input
// Must be RTC-capable pin: GPIO0-GPIO7 on ESP32-C6
// Avoid GPIO4 and GPIO5 which are used for strapping
#define SLEEP_DURATION 5 // Deep-sleep interval in seconds between wakeups
#define HEARTBEAT_INTERVAL 60 // Force a periodic telemetry heartbeat every N seconds
#define DEBOUNCE_INTERVAL_CYCLES 1000 // Minimum ULP clock cycles between valid edges to filter out noise (debouncing)
/* Anemometer conversion constants */
#define PULSES_PER_ROTATION 2.0f // Sensor pulses generated for one full rotor rotation
#define RADIUS 0.078f // Rotor radius in meters (center to cup midpoint)
#define CALIBRATION_FACTOR 2.5f // Empirical multiplier to match real wind speed
/* BLE/BTHome beacon behavior */
#define BLE_ADV_DURATION_MS 1000 // Advertising window duration after each wakeup
#define BLE_ADV_INTERVAL_UNITS 32 // BLE adv interval units (0.625 ms each): 32 = 20 ms
/* Battery measurement via ADC */
#define BATTERY_ADC_GPIO 0 // GPIO connected to battery sense divider output
// Must be an ADC-capable pin: GPIO0-GPIO6 on ESP32-C6
// Avoid GPIO4 and GPIO5 which are used for strapping
#define BATTERY_ADC_SAMPLES 1 // Number of ADC readings averaged per measurement
#define BATTERY_VOLTAGE_DIVIDER_RATIO 2.0f // Scale factor from ADC node voltage to battery voltage
#define BATTERY_MIN_MV 3200 // Battery voltage mapped to 0%
#define BATTERY_MAX_MV 4100 // Battery voltage mapped to 100%- The main CPU enters deep sleep.
- LP/ULP firmware monitors the sensor pin (
SENSOR_PIN) and increments pulse count on valid rising edges. - Every wake interval (
SLEEP_DURATION), the main CPU wakes up. - Firmware computes:
- pulse delta
- RPM
- wind speed (m/s and km/h)
- battery voltage and percentage
- BLE advertising is sent when:
- wind value changed, or
- heartbeat interval is reached
- Device returns to deep sleep.
This project is licensed under the MIT License - see the LICENSE file for details.