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layout power
title Power
permalink /power
sequence 6
power
tree components calculation source battery_life charging_duration charging_instruction
true
true
true
<code>2000mAh</code> LiPo battery
1 month
12 hours
Remove the WeMos Battery shield from the board. Plug in the USB cable to the WeMos battery shield to charge. <code>Red</code> LED will be on while it is charging.<code>Green</code> LED will be on when charging is complete.

Power consumption of main components

Chip # Chip Operating Voltage Active mode Modem-sleep mode Deep-sleep mode Total
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:

  1. Wakes up in Active mode for 30 seconds every 4 hours to read the sensor value and ping to cloud
  2. Wakes up in Mode-sleep mode for 10 seconds every 20 minutes to check whether the counter has reached the threshold
  3. 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% ⁉️