Data logger shield - turn off power to RTC / SD card?

Using Arduino Project Guidance
1

Hi all,

I'm working on a project where we want to log a distance every 5 minutes for a week, running off a single 9V battery.

Got everything working, using sleep mode and a Pro Mini + ultrasound sensor + the Adafruit data logger shield: Overview | Adafruit Data Logger Shield | Adafruit Learning System. I soldered the pro mini on top of the shield and connected all the necessary pins.

The pro mini in sleep mode consumes very little power (around 10 uA) and is only awake for a fraction of a second every 5 minutes so that's all fine.

My problem now is the RTC of the shield is being powered constantly and uses up most of the power.

Using this shield, would I be able to turn on/off the power to the RTC / (SD card)? The idea is to power it only for the time needed (ie every 5 mins).

Having a look at Nick Gammon's post on power saving (Gammon Forum : Electronics : Microprocessors : Power saving techniques for microprocessors) he explains that you can power the RTC off a digital pin to be able to turn it on/off at will.

From the shield schematic, it looks like the whole thing takes 5V from the Arduino board which feeds the RTC, and is converted to 3.3V to feed the SD card.

So my idea was to connect a digital pin of the Pro Mini to the 5V pin of the shield to be able to turn off power to the shield. However I know the SD card takes several hundred milliamps when reading/writing so I'm not sure if this is possible (I haven't actually measured curent taken by SD card).

I'm looking for solutions allowing me to turn on/off the RTC to save power.

Thanks in advance!

2

The shield consumes much more current than a digital pin can provide. I'd use an FET or relay to turn shield power on or off.

The RTC will continue running on its battery when external power is off. Don't worry, the battery will last a long time (years). And it must run continuously if you want to use it to wake up the Mini.

3

Thanks for the reply. Would a general mosfet do the job? I also need to check if I have enough space left, since with the Mini and US sensor the part of the shield where you can solder stuff on is pretty crammed already :slight_smile:

I'm also considering buying separate RTC and SD card breakouts and putting everything on perf board, seems it would make things simpler maybe.