Fig. 7
From: An open-source platform for sub-\(\textrm{g}\), sub-\(\upmu\)A data loggers
Tagbase circuit (simplified). The tag base consists of a processor (STM32F042), circuitry for a battery charger and SWD interface to the tag, and (optional) input from an external power source (LPM01A). Selection of the power source for the tag is controlled through an analog switch (SW1A). The processor can be isolated from the tag through a pair of analog switches (SW2A,SW3A). The external power source provides two power lines with programmable, but equal voltages—VDD and VOUT; the current through VOUT is measured. Voltage regulation and circuit protection components are elided