car power circuit thingy

[tehtehteh]

I have a raspberry pi running in my car with a cheap buck converter providing 5v from the ignition, I would like to do something more advanced with the shut-down but I can't think up anything ideal in my head, my knowledge is too limited, I was hoping someone here could help

currently power is cut when the engine is switched off, to delay this I would run the pi off the battery instead, but I don't want it to be continuously running

I have picaxe 8 and 14 programming boards, my first thought would be to have a picaxe running off the battery controlling a relay between the battery and the pi's buck converter. I would have the ignition on one of the inputs, the picaxe will switch on the power relay when it gets the ignition signal, then when the car is turned off the ignition signal will end, the picaxe will send a signal to the pi to commence shutdown and then the pi will send a signal back to the picaxe when it's ready and that will turn off the relay again

the problem with this is it will always be drawing a bit of battery power, also I can't get away with a simple voltage divider to turn the 12v into 5v for the picaxe because power fluctuates too much on startup, I don't want the buck converter running the whole time either so putting this before the relay is out of the question

does anyone here know a good solution?

 

[signalman72]

Have you considered a slow release or delayed relay? How much of a time period are you looking at?

 

[tehtehteh]

while I want as simple a solution as possible that is probably too simple, I have to send a signal to the pi when the ignition turns off to run the shutdown scripts, also it could be up to 20 minutes that I want to continue

 

[cjdelphi]

So what determines shutdown? Why not shut ut down then?

 

[tehtehteh]

I'm not manually shutting down every time I turn my car off

 

[sureshot]

Why over engineer it, what's wrong with a switch. Seems a lot of extra unessersery circuitry for an ignition turn off, or some would be time delay.

 

[tehtehteh]

1 - it defeats the purpose of being automatic if you have to remember to do it manually each time

2 - there's a set process of things I want the pi to run through after I turn the ignition off, culminating in a 20 minute delay, I'm not going to come back to my car after 20 minutes every time I drive it do turn something off

I'm sorry if my project offends you

 

[cjdelphi]

And offending project?

I want to know why it can't shutdown when finished with the scripts

 

[tehtehteh]

I made a mistake posting here

big thank you to the guy at the top who actually tried to make a suggestion

 

[cjdelphi]

No, i'm just confused as to what you want and what it it's already doing...

 

[tehtehteh]

the details aren't important, if you must know the setup powers a dash cam and I want it to stay on for 20 minutes after engine off

 

[sureshot]

No its not offending, I'm sorry if you saw my post as such. It was just a reply no offence intended ! Lighten up (-;

 

[cjdelphi]

Look, the switching reg uses little in standby mode..

Use a 7805 to the pic from the sw/reg to power it

Obviously some kind of script initiates after 20 mins or so, this will trigger an interrupt on the mc which powers off the pi...

I don't see a problem

 

[tehtehteh]

thank you for the suggestion, but I'd really rather not leave it running 24/7

 

[cjdelphi]

Why not? Even an lm2596 will use a few ma in stand by, putting it another way

The car battery will run it for months!

 

[tehtehteh]

yeah the battery life will probably be ok, I'd just rather not leave a cheap ebay chinese circuit running 24/7 in the car when I'm not there to put out any fires

 

[cjdelphi]

Switching regs have an internal temp sensor, which limits the current...

If they both fail?

Add a fuse, if you want to go one step further, buy a thermal fuse! - i have these running 24/7 in my home i even beat the crap out of one, all the flux bubbled, so much heat damage looks bad, still going!

These things are tougher than bruce lee, before any security add ons

 

[tehtehteh]

just thinking stuff up here, my knowledge of electronics mean I could be talking complete rubbish, but could I not have both of the power options going into the picaxe?

the ignition 12v goes into a linear regulator which then goes to power the picaxe AND provide the signal, the picaxe then turns on the relay, with the relay on the buck converter then powers the raspberry pi and also sends power back to the picaxe, then when ignition is turned off the signal ends but the picaxe is still powered and can send the shutdown signal, at the end it shuts off the relay and cuts power to everything

could it be as simple as I am saying sending 2 different sources of 12v into the picaxe? I am using yenka here and it seems ok

 

[tehtehteh]

how does this look?

 

[cjdelphi]

Inition signal in.... ah ok you step it down to 5v

Is this a 5v relay? If it's 12, it's only going to see 5v, it might struggle to energize

You're not far off ... you need a resistor on the base of the transistor or you'll risk cooking your micro controller, you could also do with smoothing caps