This repository is specific to STM systems. It primarily supports Pyboard 1.x and Pyboard D. An alternative micropower architecture is to use ESPNow with ESP8266 or ESP32. This document describes an MQTT client suitable for long term battery operation.

The Pyboard can be used to build systems with extremely low power consumption, and it is possible to build systems capable of running for over a year on standard batteries such as AA cells or even coin cells. With the Pyboard 1.x series, achieving the lowest possible power consumption where peripheral devices are attached requires a little additional hardware. The Pyboard D overcomes this requirement by virtue of a software switchable 3.3V regulator which also powers the I2C pullups.

Broadly there are two approaches, depending on the acceptable level of power consumption. If an idle current in the range of 500uA to 1mA is acceptable, code can be largely conventional with pyb.stop() being employed to reduce power consumption during periods when the Pyboard is idle.

For the lowest possible power consumption pyb.standby() must be used, cutting consumption to around 6μA. With external hardware on the Pyboard 1.x or via the switchable regulator on the D series the peripherals may be turned off ensuring that the entire system uses only this amount. The drawback of standby is that on waking the Pyboard restarts as if from a reboot. This introduces potential difficulties regarding determining the source of the wakeup and the storage of program state while sleeping.

Two sets of resources are provided to assist with the development of low power solutions.

hardware A discussion of techniques to minimise power consumption including ways to shut down attached devices, calculation of battery usage and measurements of results. A schematic for a typical system is provided with accompanying PCB layout.

upower This documents upower.py, a module providing access to features of the Pyboard SOC which are currently unsupported in the official firmware. Some of these features may be of wider use, such as using the battery backed RAM to store arbitrary Python objects and accessing the RTC registers.

All code is issued under the MIT license