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Thread: How would you power a Raspberry glovebox computer?

  1. #1
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    How would you power a Raspberry glovebox computer?

    So my idea for a summer project is fairly straightforward, but there are a few kinks to work out before I just drop several hundred dollars. I want to set up a Raspberry Pi for use with emulators, music, and video. Other than finding a suitable monitor, I think I have put together a list of all the necessary components.

    The problem is, while I am pretty good at setting up software, I have never understood cars or electricity. I need some way to power this little beast without damaging the OS. If I ever forget to turn off the Pi before I kill the engine, I don't want the little guy to just die without a proper shutdown. My biggest concern is accidentally cutting the power and potentially corrupting the SD card.

    The good news is that the Pi uses almost no power. The Pi and the powered USB hub only take 5V apiece (1000mA and 3800mA respectively), so I don't require anything close to the power of a full-size PC.
    So what do you think? What's the best way to get this thing powered? Do I just buy a cheap inverter and plug it into the cigarette lighter or what? I am considering buying one of these. http://www.amazon.com/PowerDrive-RPP...755027&sr=1-16

    What would YOU do in a situation like this?

  2. #2
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    Get one of the DC to DC convertors listed in the store if you are going to be running a number of things off of it. If you look I dare to bet your PI has a 5V DC input. All of the small arm boards I have looked at do.

    This at a minimum would require a simple 12v to 5v dc adapter that could plug into the cigarette lighter to power your device. If you are going to permanent mount it you may want to consider a version you could hard wire into your car. Many have the hardware in the plug that goes into the lighter socket. You want one with the hardware somewhere else so you can cut off the plug.

    Make sense?

    The adapter or "wall wart" that came with your pi is likely an AC-DC adapter and will say the voltage it puts out and the amperage. Pay attention to this when you get a DC-DC adapter. A screen, unless you run it directly off the PI, will likely come with its own lighter type plug but the screens I have seen are made for 12volt systems so you couldn't run both off the same adapter without some additional hardware. But check your system for details.

  3. #3
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    you don't want an inverter, that's just going DC to AC to then go back to DC for the PI and other accessories like the hub - there is wasted power on each conversion.


    to power your PI you just need a 12v to 5v adapter with an amperage the same or higher than what PI requires. the PI's normal AC adapter is rated at 3Amps, so this would work:
    http://www.amazon.com/New-Trent-high...dp/B009HD44US/

    then add this cable to go from the USB power port on that adapter to the 5.5mm barrel jack on your PI:
    http://www.amazon.com/Generic-Volt-B...dp/B00304DZ7I/

    you could get a multi-outlet extension and plug as many of those sort of combinations in as you need to power each of your accessories too, just plug into a constant-on outlet or hardwire to a constant on source to make sure it doesn't go off with the car and corrupt your PI's card:
    http://www.amazon.com/LENMAR-SPP-04-...dp/B00009RUGY/


    now the above will work and you'll never even have to strip a wire, but i would recommend against that whole approach and instead tell you to get an intelligent power supply unit from the store here:
    http://store.mp3car.com/Power_Products_s/2.htm

    the advantages to these smart supplies are:

    - most of those are rated at high enough amperage that you can use single supply to power your PI and multiple accessories.
    - some have configurable and multiple output voltages, so if you had a screen that needed a regulated 12v and the PI and a hub that needed 5V, there are ones that can do that.
    - the most important thing is that nearly all of those "survive engine cranking"... the car's voltage can drop from 12v down to as low as 7v when cranking and some power supplies can't give their rated output consistently when that happens. that essentially gives your PI and other accessories a "brown out" condition and can create all sorts of havoc.
    - secondly most important IMO is that many of them have configurable startup/shutdown controllers built in... you can set timers as to how long before which outputs shut down, ensuring that turning the key off and then back to accessory quickly doesn't kill everything unintentionally. that also can allows the PI a moment to go through it's shut-down procedures gracefully when the vehicle is turned off instead of essentially "yanking the cord".

    the only disadvantage is you will need to do some wire stripping and soldering or crimping. it's really not that hard though, most of them have instructions with diagrams for common scenarios.
    Last edited by theksmith; 05-28-2013 at 06:25 PM.

  4. #4
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    Quote Originally Posted by redheadedrod View Post
    A screen, unless you run it directly off the PI, will likely come with its own lighter type plug but the screens I have seen are made for 12volt systems so you couldn't run both off the same adapter without some additional hardware. But check your system for details.
    Really? I would have thought that the monitor would be wired to the power supply just like the old radio was. If I took a monitor and had it professionally installed, would they really just drag a wire out in front of the unit and use up my 12V socket? That seems a bit sloppy.

    And theksmith, you would recommend a smart PSU for someone who is not quite electrically savvy? I'm sure that once I got the unit, I could figure out how to hook it up properly, but on a student's budget, 100+ dollars is a lot of money. I think the smart PSU sounds like a good option, but I want to be sure I'm getting the right equipment before I drop the money.
    I took a look at the link you gave, and these units stood out.

    The M1-ATX looks like a fantastic choice, but unfortunately it looks like it is no longer produced.

    The Intelligent DC-DC converter also looks good, though I would be a bit concerned if it needed to power a 12V monitor AND two 5V accessories. I may be wrong, but it doesn't appear to be able to handle two separate voltages at the same time.

    A battery is also an intriguing idea and this one seems to fit the bill, though I have no idea where I would store a large battery.

    Any thoughts on these units? If I get one, I am confident that I can learn how to make it work, but I'm not sure that any of these are suitable.
    Just to reiterate, I would need to power 3 different devices.
    Monitor - unknown energy reqs, but presumably 12V
    Raspberry - 5V / 1000mA
    USB Hub - 5V / 3800mA

  5. #5
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    MOST of the monitors you will find for use will be re-purposed monitors designed to be used in car and would come with a mounting bracket to bolt them into your car. Because of their design they are normally 12V. The monitors I have used both have a lighter plug on them with any filtering of the power either being done in the wire its self or in the power supply inside the monitor. Normal consumers purchasing these monitors would likely just use the lighter plug. Professional installers would cut off the lighter plug and hard wire to the proper power feeds. You can feel safe to wire this directly to your car without issue. No need for a separate power supply.

    You do not want any of the MX-ATX power supplies. Those are for ATX motherboards and are NOT a simple DC-DC convertor. Make sure you are choosing a simple DC-DC convertor and NOT a pc power supply. Quite a few people are putting small but standard PC's into their vehicles and that is what these power supplies are for.

    Use of a battery would not work unless you fancy having to take the battery out and recharging it all of the time...

    The DC-DC convertor should work well for your +5 volt needs. This is the one I was thinking of when you mentioned this in the first place.
    You could also get a more expensive unit that does 2 voltages but unless you have a specific need to do so I wouldn't bother.

    If the PI you have has a LVDS connection you won't need to worry about powering the monitor because the PI will power everything. If you are using a HDMI, DVI or VGA monitor you will need a separate power supply. But as I said before, these monitors are likely to be designed to run off car power and can be wire into your cars power directly with no need for another power supply.
    Last edited by redheadedrod; 05-30-2013 at 08:03 AM.

  6. #6
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    Okay then. That sounds good. I was leaning toward option #2 anyway. I think I'll go ahead and buy the monitor and attempt to plug it into the power source that the radio was using (provided that they match up). Failing that, I'll just pay someone who does this sort of thing. Then I'll get the DC-DC converter and learn how to use it.

    Thank you both for your help. I think I know how I'm going to do this now.

  7. #7
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    someone had a kickstarter project to make a raspberry pi power supply for car use. well i think it was a controller, and you used whatever dc-stepdown supply you needed (theyre $4 on ebay, a dc-dc adjustable voltage controller with 3 amps of throughput). ignition fired, and i sent a script to shut down the pi... it would even hard-off after a set time in case the shutdown didnt work.

    i cant find the guy though... he was supposed to be shipping them by now

  8. #8
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    Quote Originally Posted by trader007 View Post
    someone had a kickstarter project to make a raspberry pi power supply for car use. well i think it was a controller, and you used whatever dc-stepdown supply you needed (theyre $4 on ebay, a dc-dc adjustable voltage controller with 3 amps of throughput). ignition fired, and i sent a script to shut down the pi... it would even hard-off after a set time in case the shutdown didnt work.

    i cant find the guy though... he was supposed to be shipping them by now
    I think that is called "pi supply". They are here: http://www.kickstarter.com/projects/...or-raspberry-p.

    I have also been making a carputer with the pi. I have all the easy stuff done, but the power supply is still bugging me. My setup is discussed here: http://vanputer.blogspot.com and I am at the point where I need to do a more permanent power solution. Right now I have:

    12V lighter adapter -> usb -> RPi

    When I turn off the ignition, the thing just crashes. I am hoping to get something like the intelligent car adapters you are discussing above, but one that can plug into a lighter, send a shutdown signal, and plug into the RPi. I am not much for hardware hacking so I have no idea where to begin. I was looking at this power supply (which I believe is the same one as above) but needing to make the wiring on each side stopped me cold. I have no idea what the names of those plugs are, let alone how to safely wire it all up. Maybe if I knew the types of plugs I could find adapters to go from 12v to the power supply. Then I have to do the same to get back out to USB - my RPi is a rev B and only has USB power.

    I want...

    12V lighter adapter -> something smart enough to power the RPi and send a shutoff signal out via usb and GPIO -> RPi

    Maybe if someone could tell me what those plug types were and how to make them end up in a USB input, I would put it all together and post it back here...

    I can definitely strip wires.

    Thanks,

    Judd

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