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I have a circuit that consumes enough power to keep running from a powerbank. However, to save energy I'm putting it in low energy mode at night.

Problem with powerbanks, they turn off when not enough power is consumed. My proposed solution was creating a separate low-power circuit that times how long the powerbank is off and at the right moment provides a short burst of power. The devices in my circuit then turn on, the powerbank detects this and also turns on.

All the devices in my circuit are Arduinos or Arduino compatible running on 5V. The circuit pulls a maximum of 200mA. I have no physical input on the system as it is placed in a different location. Everything needs to be automated. It preferably has to use the powerbank due to portability and the desire of having no external wires.

What is a safe method for an external circuit, to turn on another circuit in an automated way?

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  • $\begingroup$ Huh? What's this "powerbank" thing? $\endgroup$ – Olin Lathrop Jul 8 '16 at 11:15
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    $\begingroup$ Basically a battery but with regulated 5V output and USB connection. Example. $\endgroup$ – Len Jul 8 '16 at 11:25
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The problem is the Powerbank detects when nothing is drawing power, assumes nothing is connected to it and shuts down. Your circuit doesn't draw enough current to be detected.

One solution - program your controller to wake up from its low power state once a minute, flash an LED for a few seconds to draw some current, then go to sleep again.

(You will need to do some experiments to determine if once a minute is enough, and also if a single LED is enough load.)

I've heard quite a few people on the internet discuss this: for example here is a solution someone invented that draws current off one of the Powerbank's USB outputs.

(Personally I avoid this by just making little packs of, say, ten NiMh AA cells but they're more bulky of course.)

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  • $\begingroup$ Thanks for your response. That's exactly the problem with powerbanks. I want to develop a portable device that can run on a single charge for a few weeks. I thought about AA batteries, but they are indeed bulky, heavy and need to be replaced every single time. Things like powerbanks can be charged easily which is beneficent for my wallet and the environment. The solution you propose is not what I want to do, as it would still draw current. In that case it would be better for me to keep the Arduino on, but that draws too much power for the long run. It's quite the bummer. $\endgroup$ – Len Jul 8 '16 at 13:59
  • $\begingroup$ Would using Li-Po be a proper solution? Just hook up several high mAh Li-Po's to a converter to boost the output from 3.7 to 5V. But, hooking up multiple Li-Pos makes me wonder about safety and fire hazards. $\endgroup$ – Len Jul 8 '16 at 13:59
  • $\begingroup$ @Len, I think the point of the solution I mentioned is though it draws a little power, it's far less than running the system continuously. So still quite a good saving. Also for general low power tips (not powerbank though), try Nick gammon's forum $\endgroup$ – Andy Jul 8 '16 at 14:51
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    $\begingroup$ Thanks for your input. I found Nick's post as well, very interesting so I'll look into that. $\endgroup$ – Len Jul 11 '16 at 7:27

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