RaspberryBox 2PIr – The power brick

So I have been doing research on this here and there for a while. It represents a lot of challenges for me, being my first time diving into a linux distribution, first real attempt at soldering, and some tricky things to figure out regarding compatibility between pi and 360 components. Thankfully a lot of research on that latter part has been done by others.

With the 360’s power brick, while I can’t find anyone else who’s used it specifically for a raspberry pi before, there are a ton of resources online for using it for any number of other projects. Most of the information I found was very project agnostic – they didn’t even mention what they were using it for other than to say it was used as a “power supply”.

I had already decided I’d be ripping the power-in port from the 360’s motherboard (I actually ended up just using a hacksaw to rip that whole section of motherboard off, since my soldering iron didn’t get hot enough to remove it from the board altogether).
I found this video which talks about using the brick as a power supply by chopping off the plug at the end and exposing the wires. Obviously that last part isn’t what I’m after, but the video does talk about the voltages available from the brick, as well as how the ‘power okay’ and power short protection works on it, which was the basis for the circuit I decided on.

I found the below image from this forum post which laid out for me where I need to solder onto the port.

The 12v positive connections are all connected internally, likewise with the grounds.
No power will go through the 12v connections unless the 5v standby and pwr enable connections are shorted.
With that in mind, I just had to connect the 5v to the positive side of a red LED, the negative of the LED to a resistor (interestingly either side of the resistor works fine), and then from the other end of the resistor to the pwr enable. And of course I slapped a switch in there (before the LED on the positive end if I recall). This is especially important, since the raspberry pi doesn’t actually have a power button – it boots up as soon as there’s power going to it.
Thankfully I got that working first try! Not bad for a first solder job, wouldn’t ya say?

You’ll notice in the video that the LED on the power brick changes from orange to green when I switch it on and think that makes my red LED redundant! You’d be right! But I like to be able to just glance behind the machine to see if there’s power rather than fish under the tv stand to find the brick. It’s a useful redundancy.

Also I could have used just the 5v power for the pi and attached a switch to it (as shown in that youtube video), but I wanted to have an LED on the back of the console to indicate when power is going to the device, which would obviously be taking voltage away from the pi, which is not ideal. Not sure if that would have worked or not, but I didn’t wanna risk it.

So as I’m using the 12v power, and the pi requires 5v power, I had to get a 12V DC to 5V DC step down converter! Don’t ask me how these work, I honestly don’t know. What I do know is that they take the 12v power and bring it down to 5v, normally with a max output of 3amps. Which is great, because that’s about right for a pi using external harddrives!
There are a ton of step down convertors available on ebay/trademe/etc. I just bought the cheapest one, which also turned out to have its own encasing, which means I don’t have to worry about it shorting on the 360’s case. Handy!

All I had to do was connect the converter’s inputs to the 12v connectors, and the outputs to the red and black wires on a mini USB male head, which I ripped off a cable I had lying around. The other end will come in handy later.

I did some quick tests with a multimeter to check that all the connections are okay and the step down converter is doing its job nicely, then plugged in the pi! Success!

I used the instruction manual to make sure the micro USB wires didn’t short, since I hadn’t wrapped them up yet. But yeah, as you can see, the power conversion works nicely!
I have a second step-down converter in case the pi has trouble powering more than one HDD at a time – I can power a USB hub with it to fix that problem if it arises.

I took the chance here to do a quick update (sudo apt-get update and sudo apt-get upgrade) and then shut it down. Next step is to get the RF unit and all the buttons wired up.

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