Power overview

Power source

2000mAh LiPo battery

Battery life

1 month

Charging duration

12 hours

Remove the WeMos Battery shield from the board. Plug in the USB cable to the WeMos battery shield to charge. Red LED will be on while it is charging.Green LED will be on when charging is complete.

Power tree schematic

Edit power_tree_drawio.xml at draw.io.

Power consumption of main components

Chip #	Chip	Operating Voltage	Active mode	Modem-sleep mode	Deep-sleep mode
ESP8266	WiFi based MCU	3.3V	170mA	15mA	10uA
Si7021	Temperature / Humidity sensor	1.9V - 3.6V	150uA		60nA
SN4HC595	Shift register	2V - 6V	60uA		1uA
Total consumption			170.23mA	15mA	11.06uA

Total duration: 30s.
Total duration in Modem-sleep mode: 10s x 12 = 120s.
Total duration in Deep-sleep mode: 4h.
Total charge in Active mode: 30/14400 * 170.21m = 0.354 mAs
Total charge in Modem-sleep mode: 120/14400 * 15m = 0.125mAs
Total charge in Deep-sleep mode: 14250/14400 * 11.06u = 0.011mAs
Total charge: 0.589mAs

Power calculation

3 power modes:

Wakes up in Active mode for 30 seconds every 4 hours to read the sensor value and ping to cloud
Wakes up in Mode-sleep mode for 10 seconds every 20 minutes to check whether the counter has reached the threshold
Deep-sleep mode for the rest of the time, unless user button pressed

1200mAh battery will last for (1200/24/30) = 2.89 months

Measuring power

Mode	Pins	Voltage
Deep sleep	`5V` - `GND` on WeMos D1 mini	`4.94V`
Deep sleep	`Vin` - `GND` on Si7021 breakout board	`5V`
Deep sleep	`Vcc` - `GND` on 74HC595 chip	`5V`
Deep sleep	`EN` - `GND` on 74HC595 chip

Actual vs. calculated power

Periodic wakeup	Calculated	Actual	Error %
6 hours	2.89 months	30 days	~300% ⁉️

Cactus