5v Arduino Mini Pro Evening Power Down Suggestions

I have setup a 5v Adruino Mini Pro powered initially by a 17v solar panel to a set of 3 18650 batteries (that is controlled by a TP4056 charging board) to a buck step down converter giving a constant 5v output. This drives a 5v pump in a Japanese water fountain that I have built using bamboo (well recycled didgeridoos!). This is working fine during the day but there is no need for it to be working at night. So I added a Photocell to the Mini Pro that switchs on a digital pin when the Photocell is reading above 300. I am using the “delay” function to only check the Photocell every 15 minutes. But the Mini Pro is still powered up 24 * 7 when it doesn’t need to be using battery power. So I am thinking about using the LowPower.power down function to put the processor to sleep for 8 seconds at a time (the longest I think I can do). This drops the drain of the processor down from about 15mA to 6uA apparently. So very good. The problem is 8 seconds is not long so how would you suggest I put the processor to sleep for say at least 8 hours? It would be great to use the PhotoCell to restart the processor but it all becomes a bit circular at that stage as putting the processor to sleep will also stop the Photocell. Would appreciate your thoughts ! :slightly_smiling_face:

It’s a bit outside my area of expertise but can’t you use that same photocell (maybe with some additional electronics) to wake the pro Mini up again using an interrupt?

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Just put it back to sleep after the 8 seconds. A burst of 15mA every 8 seconds will not drain the battery noticeably.

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Put it to sleep, wake up after 8 seconds , increment a counter , go back to sleep
when the counter reaches a set value , stay awake , power the LDR , check light level .
Reset the counter .Then sleep again or put the light on

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Would you happen to have any sample code using an Interrupt to wake the Mini pro or my Photocell?

Have a look at https://www.gammon.com.au/power, sketch J.

The trouble is that you then need more analog circuitry to turn the photocell voltage into a digital control signal and that analog circuitry itself would tend to consume current.

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