Battery-wise AI/DI

Hardware
1

To date, I’ve always powered my AI/DI from 3.3 on the April/P3V0 breakout boards, pulling them to ground with a 10K resistor. The boards have always been powered via an AC adapter. This works well for my thermistor inputs as well as simple contact closures.

I now have a project utilizing TheMakeDeck’s C3V0+ in a battery-powered application in which I desire reasonably long battery life (a few weeks, at least). I believe I’d be wise to give up one of the ports and use it as a DO to power any external AI/DI devices in lieu of the 3.3. I would expect to program the device to wake up, turn on the DO when I need to read what will likely be one/more DI contact closures, turn it off afterwards and put the device back to sleep until the next cycle. The application is an ad hoc temp, humidity, equipment status logging device for troubleshooting purposes. Yes, I’ll be using the onboard Si7021 for the temp & humidity.

Is this wise (obvious?) or am I being a bit too concerned. From a quick calculation, it would seem the current draw (0.00033A) through the 10K is too low to worry about, but…I’ll admit I may be missing something. I also hate to give up a port that may be needed in the future as a DI/AI.

2

Quick thoughts… Remember that the C3V0 has a 3.0V rail instead of 3.3V… usually not a big deal for most sensors. I don’t think you’ll be able to power a sensor through one of the pins… typically you would use one to enable a FET to power the sensor and then read it with another pin(s). However… most sensors have a very low Iq, so hooking it directly to the 3V rail should be fine. I may be misunderstanding your intent though…

3

If the imp is staying on, i.e. it’s in shallow sleep, then 330uA is a negligible part of the 4,000uA total. If the imp is in deep sleep, then 330uA is 95% of your power consumption – the imp will be taking 6uA.

Peter

4

@MakeDeck - good catch on the 3.0V rail–I had missed that. However, it’s rather academic, since all I’m doing is pulling the port to ground via a 10K and using something like a thermistor or normally open switch to connected to the port and the rail.

5

You should be ok powering low consumption things from an IO pin. Ensure you have bypass cap there though, as it is a current limited supply.