Day: November 29, 2018

Don’t know how to determine battery capacity for EFM32 Happy Gecko nodes


I have a couple of Silicon Labs EFM32 Happy Gecko modules (info) that I want to use to measure temperature, relative humidity, CO2 (ppm) and if possible air flow. I’m trying to get at least three years out of one battery cycle, but preferably I would like to be able to use it for five years. I send the data over LoRa, with the RN2488 chip.

My problem now is that I don’t know what battery to choose. What voltage to work at? What capacity does the battery need to have?

Voltage range EFM32 HG: 0 to 3.8V

Voltage range RN2488: 2.1 to 3.6V

Current consumption RN2488: Datasheet RN2488 page 22

I tried to make an estimation with this calculation (I’m pretty sure there is a mistake in there):

 Battery: 2Ah at 3V (does not include RN2488 chip) MCU: 160 µA/MHz -> 160 µA each million clock cycli? -> energy consumption MCU per second: 160 µA -> per hour: 160 * 10^(-6) * 3600 = 0.576A 2Ah * 3600s = 7200 Coulomb -> 7200C / 0.576C/s = 12,500 seconds or 3.47 hours If we assume that the MCU only calculates 0.5% of the time (0.5% of a day is 7.2 minutes that the MCU is calculating) and the MCU is completely off the rest of the time (to make calculations easy): 694.4h on one battery charge = 28.9 days. 

Can anyone help me with an estimation on voltage and battery capacity? Or can anyone give me tips how I can look for batteries myself?

Thanks in advance.

Edit: if my method of calculation is correct, I can try to make a more complex equation with the battery capacity as unknown variable and with energy consumption of the RN2488 chip and energy modes of the HG board included.

submitted by /u/mich2000222
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