Upgrading My Stereo PART 2: Connecting the Power and Audio System
This is the second post outlining how I upgraded the basic stereo system in my van to something that would sound much better and be a lot more fun to use!
In this post I’ll guide you through how I connected the power and the audio system for my Raspberry Pi Touchscreen Head Unit.
The Raspberry Pi would provide the music but it wouldn’t be able to drive a pair of speakers on its own. For this I needed an amplifier. The previous amplifier and speakers were really basic and sounded crap so I decided to replace them both.
I found this tiny amp second hand on eBay for £14.00. This is a LEPY LP-2020A Class D Amplifier. It runs from 12v and could therefore be powered straight from my leisure batteries. Perfect!
I had previously made an enclosure above the centre console on the ceiling of the cab. I’d wired a pair of terminals connected to the fuse box of my van and a power switch. Luckily it was big enough to house the amplifier and with a few modifications I installed it without much trouble.
I made a hole in the front of the box big enough for the amplifier face plate.
Then secured the amplifier with two screws. The enclosure was just big enough!
Providing power to the amplifier was pretty straightforward. It takes 12v DC which I already had running to the enclosure from my leisure batteries.
I chopped the barrel connector end off the mains supply included with the amp and then connected it to the power terminals in the enclosure.
It normally shows which part of the connector is positive on the back of the plug, in this case the middle of the barrel. I used a multi-meter set to the ‘continuity’ setting to trace which wire was positive and connected it accordingly.
The Raspberry Pi was a bit more tricky. It takes a 5V supply either from a micro USB connection or connected straight into the GPIO pins. I wanted to use the micro USB to provide power as it gives some extra protection against voltage surging.
The screen takes its power from the Pi so the supply needed to be able to provide power for both, to be safe this should be about 3A . Initially I connected an in-car USB 12v charger with an output of 2.1A. It worked but a few seconds into the boot sequence the screen flashed up with the ‘low power’ icon (a lightning bolt on this version).
I didn’t want to risk damaging the Pi so I had to find another way to provide more power. I found a solution with an adjustable DC – DC 12A Buck Converter that I found on Amazon here for about £9: https://amzn.to/2AF02Xn
This nifty little fellow accepts a wide range of input voltages ( 4.5 – 30V) and outputs a voltage dependant on what is set by the user. Before powering anything you’ll need to connect the converter to your power supply and then use a multimeter on the output pins whilst twiddling the little screw to set the correct output voltage, in my case this was 5V.
Once this was set I ran a length of 2mm² wire from the output of the Buck Converter down to my centre console. I snipped an old Mirco USB cable and connected the red and black wires to the corresponding cables using a choc block. The micro USB cable I used had two additional wires, green and white. These are for data transfer so didn’t need to be connected.
I then wired the positive power connection from my leisure batteries through the switch next to the amplifier so that I could turn the Pi on and off easily.
The last step was to connect the audio cables from the amp to the Pi and the amp to the speakers.
I bought a pair of FLI Audio Integrator 6″ Speakers and mounted them either side of the cab. Given the drivers are only 6″ I was a bit worried they might not be very bassy but after some testing I’m very impressed with the overall sound and bass response. Great value for money and quite balanced for a car speaker.
You can find them here on Amazon: https://amzn.to/2FqgEG9
Eliminating Ground Noise
When I first turned the Pi on with everything connected, there was a horrible clicking, buzzing sound through the speakers. This was because I was using the same power source for both Pi and amplifier and it created a ‘ground loop’.
To fix this I bought a cheap ‘ground loop isolator’ from amazon here: https://amzn.to/2RGxWVq
I connected this in between the audio output of the Pi and the input of the amplifier. Ouala! No more horrible noise.
The music tracks for the system would be stored on a USB drive which would make it easier to update and add more tracks if I wanted. I would also need to connect a keyboard to the Pi to update software and perform maintenance if required.
I didn’t want to be flipping the screen backwards and forwards every time so I decided that a separate USB hub was a good option.
I really wanted the USB hub to be out of sight and after toying with a few ideas I found a great place to hide the hub in the ashtray that sat directly behind the screen. This was perfect. It was close to the Pi and could also be concealed by a sliding lid.
I removed the tray and found an appropriately sized USB hub.
The ashtray was a bit rusty so I took it apart and treated it with some Jenolite rust killer and also removed the ‘cigarette stubby outy bit’.
I then sprayed it black (obviously!) and cut a hole in the side for the USB cable.
Once it was dry, I reassembled the ashtray, popped the lid back on and secured it back into the dashboard. I love it, so sneaky!
Here is a diagram of the whole system:
Despite being fairly cheap, I’m really pleased with the sound quality of the system. It’s so much better than what was in there before and the touchscreen makes it a breeze to navigate through folders of mp3s (something that I find really difficult with standard head units!).
The amp and speakers pair well and the sound is detailed and powerful for the size of the speakers. When I turn the volume up, I feel like the amp has plenty more power to give than these speakers can handle which is impressive considering its only rated at 20 Watts per channel RMS. I think the amp could comfortably drive a pair of 6x9s or a reasonable pair of bookshelf speakers.
Obviously, when living off-grid, tracking the amount of power you’re using is important.
After some testing at various volumes I noted that the power usage was:
- 8 – 10 Watts with the screen on
- 5 – 6 Watts when the screen went into sleep mode.
This is a tiny amount of power for the sound that was being produced, I’m really pleased with this. Because it’s connected to my leisure batteries I don’t have to worry about it draining the van starter battery, which is a nice bonus!
Catch my next post to see how I configured some open-source media centre software to become a touchscreen, stand-alone music player.