Considerations of Power consumption on LoRa Nodes

After designing and building 2 types of Low Power LoRa nodes I did some measurements and calculations. I hope it will benefit your considerations how to use and program Low Power LoRa nodes.

I’ve measured the current by putting a resistor (10 or 1 Ohm) in series with the power supply (3V3). With a digital oscilloscope I measured the Voltage and then calculated the Current.

Number of pulses with high current

One pulse ATtiny84 Low Power LoRa node
Three pulsed on MiniPill LoRa node
Total time of low current consumption on MiniPill LoRa node

As shown in the diagrams above the ATtiny84 node only shows one pulse because it is programmed this way. The MiniPill LoRa shows three pulses: one for sending data and two for the receiving windows after 1 and 2 seconds. You can also see the time the processor is running during about 6 seconds. This will use also an amount of power.

Power calculations of ATtiny84 node with 5 minutes interval
Power calculations of MiniPill LoRa with 5 minutes interval
Power Calculations of MiniPill LoRa with 15 minutes interval

Conclusion

After measuring and calculation the power consumption you can draw a few conclusions:

  • The lowest power on sending data is just sending data and not wait for downlink data. Remember you need downlink data by using OTAA, but only for getting the “device address”.
  • The time the controller is not in sleep mode should be reduced to minimise power consumption during data acquisition and preparing data for sending.
  • To extend lifetime of the battery you can extend the interval when the sleep current is very low and you do not need very often updated data.

For the MiniPill LoRa board a few updates on the software might be possible to achieve lower power consumption.

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