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Message from discussion GPIO Interface hardware & Power Maintenance
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Stefan Lacombe  
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 More options Sep 5 2012, 9:45 pm
From: Stefan Lacombe <stefanlaco...@gmail.com>
Date: Thu, 6 Sep 2012 11:36:24 +1000
Local: Wed, Sep 5 2012 9:36 pm
Subject: Re: [CCHS] GPIO Interface hardware & Power Maintenance
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Not sure if this helps, but there is normally a permanent 12v and an
ignition switched 12v supply the the radio in a car.  The RasPi could be
permanently on but in a sleep mode (if it has such a thing) and made to
wake on the switched 12v signal. That's how the radio retains it's memory
when the ignition if off.

Stef

On 06/09/2012 11:31 AM, "kspn" <ksp...@gmail.com> wrote:

Hi David,

I did consider that, but unfortunately as described above (note I have
Revision 1 without a reset switch) I would have no way of turning the
device back on.

My basic scenario for this is:
1) Turn car on
2) Enable power from a battery pack (Which I have)
3) RasPi turns on
4) RasPi sets a signal to 'high' to keep power form the Battery Pack 'On'
(don't know how to do this bit)
5) Car Turns Off
6) RasPi detects that car is no longer sending Power to the battery pack
(don't know how to do this bit)
7) RasPi Shuts Down, stopping the 'high' maintenance signal
8) Power from Battery pack is turned off after a small delay (don't know
how to do this bit)
9) Entire setup now has no power, GoTo 1

This scenario is designed in such a way that the Car is turning the RasPi
on/off depending on if it is running with the limitation of the on/off
being Power On/Power Off

I will probably come along to the CCHS meeting on Saturday morning, which
may help with some of the explanation of what I am trying to achieve with
this.

As far as the switches go, I am looking for Simple, the simpler the better,
at the moment my solution is 'too' simple, and I am having to do some high
speed loops to read the GPIO pins and get the status of the buttons (I have
4), which is not ideal.
I am going to investigate the option for setting up a flip-flop so that I
only have to check the button whenever I update the screen (once per
second) as that seems to be the next simplest solution, it also means that
I can use the same code for signal checking and power maintenance for the
power issue that I am having.

Thanks
Karel

On Tuesday, September 4, 2012 5:08:44 PM UTC+10, David Lyon wrote:

> On Tue, Sep 4, 2012 at 3:37 PM, kspn <ksp...@gmail.com> wrote:

>> Hi All,
>> 2) The seco...

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