As a fan of wireless tech I always had an intention to have most smart home devices to be battery operated. This project is an intention to build a wireless board that will be able to operate efficiently on battery. Not only act as an efficient sensor (which is also some kind of challenge) but also be able to directly control external devices.

The core of the board is nrf52832 which as I learned during some work duties is extremely efficient for battery operation. I also found that MySenors library can work efficiently on it and draw as low as few uA in suspend mode and stay within < 10uA while maintaining periodic exchange of messages.

For the power source board can work from internal 3v battery (2477) or external power from 3.3v to 12v. Board has an extremely efficient DCDC power supply that is based on LTC3103. In real application I personally used both options. One of application I've used it is battery operated water leak detector. Water leak detector is powered from a 3s lithium battery (11.2v) which is strong enough to drive water valve. Eventually water leak spends all the time in the idle mode just checking for water leak and is supposed to shoot once when water leak is detected. In this idle mode board can draw about 3-5 uA from 11.2v battery and can stay years without maintenance. With 3v 2477 battery I've used it as a controller for gas boiler. This controller is reporting and maintaining desired temperature of coolant which in turn is managed by some weather and climate dependent logic. On 1000 mAh 2477 battery board can last several years.

Looking to possible sensors or actuator connections board offers:

• 2 inputs for generic and widely available 10k PTC thermistors. Through all possible options this is most cheap, battery efficient yet precise enough way to measure temperature. Battery efficiency is achieved by possibility to toggle power on the thermistor for a very short amount of time. Don't get it wrong, in classic R+PTC measurement scheme total resistance is ~20k which gives 15 uA of power consumption for constant measurement which is bigger than MCU + build in DCDC. In other words, 15 uA in battery operated world is really big value.
• 3 GPIO pins. These pins can be used to connect external i2C or serial sensors actuator if required
• 2 GPIO/ADC pins with optional jumper controlled 1/5 voltage divider
• 2 managed power lines with jumper selected 3v or external voltage source. These lines can be used to power external sensors and I've used this to control generic Arduino water leak sensor. This also part of power optimization strategy.

For built-in actuators board offers a pair of latching relays. Latching relay keeps it state without necessity to power it and toggled by current impulse. Board is routed to support either EC2-T3ENU (2A current) or HF163F-L/3-HL2T (8A current).