Battery Capacity Considerations for IoT-based Project

Hello guys from the Arduino Forum!

We are almost finished with our proof-of-concept, IoT-based fire and panic alarm project and I'm still having problems on which battery should I be choosing to power our sensor nodes in terms of capacity.

We'd be using Arduino Pro Minis, XBee S2 2mW radios, LM35s, some LEDs, a smoke detector circuit (based on A5368CA IC) and some buttons. Should someone require the circuit schematic, I'll be posting it after a short while.

Thank you very much. :slight_smile:

Just read the specs of the parts being used and sum up the current consumption. Multiply that by the time You want the project to run and You have the needed battory capacity.

The wireless is the wildcard here. That takes up a lot of power, but you can shut them down when not in use for long battery life.

Same for (most of) the other components. It just depends on how quick you want the thing to be able to react.

rayrayrayyourboat:
We are almost finished with our proof-of-concept, IoT-based fire and panic alarm project and I'm still having problems on which battery should I be choosing to power our sensor nodes in terms of capacity.

By 'proof of concept' do you mean you have not got all the equipment assembled and working so you can measure it ?

Data sheets can help with some calculations, but then you need to know how long the various components are active and consuming current.

@ Railroader
Okay. But how about if some of the modules are on for only about a certain amount of time? For sure the XBee and Pro Mini (5V) will consume the most current. I have the XBees running as routers as well so no sleeping there. Moreover, I have a polling mechanism for the system coordinator to check the devices are still active or not.

@ wvmarle
I don't think I'll be using any sleep here for the XBees. But yeah perhaps I could "shut down the device, most probably the Arduino when battery is nearing the empty threshold.

@srnet
I've got it all working quite well (just not perfect in a way I want or expect it be) in a PCB layout but it's still the battery I'm not sure about. It just affects my completion of the enclosure dimensions for the battery slot as well as with the fact that I'm not sure if it would power the device for at least 2 hours.

You can get an Amp/Hour meter (that reads in MA/Hours) and stick it in the circuit and see what the power used over time is - makes calcs a bit easier - remember to add a safety factor for high use days and the battery capacity being reduced with age

This is one I have: Watt's Up Meter - PRT-14331 - SparkFun Electronics

Well, that's simple to settle.

  1. grab your multimeter, see how much current your contraption takes. Try again while actively sending data (or check the data sheet on the difference - chances are it's so little time it doesn't matter much).
  2. take that value (in mA), multiply by 2, and you get the mAh of power your contraption will use.

Of course you want it to run for at least two hours, guaranteed, so double that number. Now you have the minimum mAh rating of the battery you need. Take the next largest battery you can find.