Power supply

The main power source is a rechargeable lithium polymer (Li-Po) battery. The battery has a nominal capacity of 1440 mAh and it can be recharged through USB.

Thingy has a power switch that physically disconnects the battery and the USB power from the rest of the circuits. This switch must be on in order for Thingy to work and to charge the battery. A voltage divider circuit is connected to the USB power so the MCU can detect when a USB cable is connected.

Figure 1. Schematics for USB and battery connectors, and the power switch

A battery charger circuit is present on Thingy in order to charge the battery. The max charge current is set to 0.5 C. Battery charge status output is connected to the MCU. While the charger has a thermistor input, the battery used in Thingy has no internal thermistor. Therefore, there is a thermistor on the main circuit board to monitor the temperature in the casing.

Figure 2. Battery charger schematic

To provide the circuits with a stable voltage, a DC/DC buck regulator with an output of 3.3 V is used.

Figure 3. Voltage regulator schematic

To save power during sleep mode, an analog switch is used to turn off the VDD power net. The low-power accelerometer and nRF52832 are powered directly from VREG and will always be powered to wake up Thingy.

Figure 4. VDD power switch schematic

To monitor the battery voltage, a voltage divider circuit is connected to the battery. nRF52832 will use the ADC to read out the voltage level. To avoid unnecessary current drain, the voltage divider is turned off with a transistor when not in use.

Figure 5. Battery monitoring schematic