Traditionally, mmWave sensors are power-hungry and their placement is often constrained by the outlet locations.
Therefore, I’ve built a battery-powered one that has an expected battery life of around 2-3 months. It has a extremely low stand-by current of only 6-9 uA, and I’ve probably reduced it down further by disabling the logger component. Compaired to commercial solutions, this reduced the cost significantly to only 58 CNY (8 USD). It is also rechargeable with a 18650 battery, and you could add 1 more cell to increase battery life. Most importantly, you can use this even in the bathroom as it is can be water-proof.
The working principle behind this is to use a PIR sensor as a trigger to wake up the esp32c3. Transmitt the “presence” signal and go to sleep. When the PIR no longer detects movement, check the mmWave sensor to see if there’s anyone here before transmitting the “absence” signal. Because anyone leaving must trigger the PIR again, it can save a lot of power by not having the mmWave sensor constantly running. This method is suitable for most mmWave sensor
But then the LD2410S sensor came out and it advertised the exceptionally low power draw. So this new design simplified things a bit by not needing to have a transistor to turn on/off the mmWave sensor.
I also used BLE broadcast instead of Wi-Fi + API/mqtt to reduce the power consumption even further. The “active” current is just 80-90mA, and it just lasts for fractions of a second. To recieve the broadcast, just use another esphome device and the esp32_ble_tracker: component.
