The heart of the Wemos Board used in our Weather Station is an ESP8266 SOC which is a power hungry chip. Our objective is to run the device by using a 18650 battery but the demand for power usually makes battery operation impractical.

Another problem is that as the device will run continuously, it is quite obvious that the device will experience warming, and therefore the measured temperature will be higher than the ambient temperature.

From the above, it is clear that we have to lower the power consumption of the ESP8266 WiFi chip. To do that, we’ll use the Deep Sleep mode which is the most power efficient option for ESP chip. It allows to put the ESP8266 into hibernation and saves the battery. You can wake up it at regular intervals to make measurements and publish them.

Component Operation mode ----- Sleep mode

1. ESP8266 170 mA -------- 10 uA

2. CH340 12 mA --------- 50 uA

3. Built in LED 3 mA ----------- 0 uA

4. Voltage monitor 0.006 mA ----- 6 uA

-----------------------------------

Total185 mA ---- 66 uA

If the sleep-wake cycle is 10 minutes, with a 30 second wake time, the energy consumption budget looks like this:

Wake time 185 mA for 0.5 minutes = 92.5 mA-minutes

Sleep time 0.066 mA for 9.5 minutes = 0.627 mA-minutes

Total in 10 minutes = 93.13 mA-minutes

Thus the average current consumption is 9.3 mA.