how to turning back on after recharge


10 posts
by texaspete » Fri Jul 06, 2012 5:56 pm
Can someone help me figure this out? Lets say I have a raspberry pi running outside off a battery and the battery dies. If I have some kind of trickle charger feeding the battery, at some point the battery will have enough power to run things. Would the raspberry pi turn back on as soon as there is enough charge in the battery (and perhaps right back off again when it falls below the needed threshold)? Ideally I hope for something that can charge itself during the day and turn on for a little bit at night. Where can I find some information on a design for this?

Thanks
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by mahjongg » Fri Jul 06, 2012 5:59 pm
Sounds like you want to connect a raw battery to the PI, which won't work, the PI needs a voltage regulated to 5 Volt, with just a 5% tolerance (4.75 to 5.25 Volt).
So you need some kind of converter, and the question becomes, when does the converter turn on.
When it does the PI will turn on too.
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by Gert van Loo » Fri Jul 06, 2012 8:05 pm
The other problem is that the Pi does not yet really switch off. When it shuts down it keeps using power (rather a lot) so your battery will not recharge
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by jecxjo » Sat Jul 07, 2012 2:15 am
You could attempt to build a low power cut off circuit that would regulate the connection between the Pi and the battery. Using a 555 Timer you can create a switch that goes Vcc or Gnd based on the difference between an input voltage and a reference. The reference voltage will be the difficult part if you are looking at a non-constant charging source (solar panel, wind generator, etc).

Doing a quick google search I found this page that describes a design for a low power cut off circuit for an Amateur Radio Repeater system. Might be a good place to start.

http://gorum.ca/lvdisc.html
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by mahjongg » Sat Jul 07, 2012 2:34 pm
Gert van Loo wrote:The other problem is that the Pi does not yet really switch off. When it shuts down it keeps using power (rather a lot) so your battery will not recharge


A little addendum is in place here. Newer distro's shut down in a new way that uses much less power.
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by higwoth1 » Sat Jul 07, 2012 3:11 pm
Yeah, I noticed that yesterday. The chips go cold on shutdown, so must be in sleep state, maybe deep sleep?

I wonder if the Pi can be woken up with a GPIO interrupt?
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by mahjongg » Sun Jul 08, 2012 3:08 pm
In principle this could be possible, as any of the GPIO's is capable of causing an interrupt.
But I dare say such a thing is probably not yet implemented.
The problem would be which GPIO would be chosen to be capable of doing this.
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by zardoz99 » Sun Jul 08, 2012 3:14 pm
Just tickle the SoC reset line.

"If you check the schematics you find that the BCM2835 RUN pin (D15) is pulled high through a 100K resistor (R15). Pull pin 1 of R15 low to have a reset." (this is a reply copied from Gert).

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by higwoth1 » Mon Jul 09, 2012 2:37 pm
Thanks.

Just to confirm, having found R15/D15 on the schematics, do you mean pin 1 on the GPIO port?
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by zardoz99 » Mon Jul 09, 2012 2:41 pm
higwoth1 wrote:Thanks.

Just to confirm, having found R15/D15 on the schematics, do you mean pin 1 on the GPIO port?


No, I think he means the end of the R15 resistor and nothing to do with GPIO pins at all.
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