The Making of an Android Auto Demo Unit

Android Auto is a protocol developed by Google to allow mobile devices to be controlled by a car head unit. This means you can use Google Maps navigation, play music, get notifications of important happenings, all from your car dashboard. The official page has more [](

Here we are going to show you how we put together an Android Auto demonstration box, this is so Novoda can use it to help our clients write apps for awesome automobile experiences. Inspiration was from the original demo units that where demonstrated at Google I/O this year. You cannot purchase them as an item and we figured, we want one!


This post was originally going to be cookbook style. However after creating our demonstration box we have learnt the same recipe doesn’t work for everybody. Whilst creating our box Google came out with their [own DIY how-to]( This was too late for us and reading it now looks like it makes a lot of assumptions. So here we will outline the steps you need to take, but really detailed specifics are not necessary as these will vary depending on the shop / country / unit system you adhere to.

The idea is to have a car head unit powered off the mains running Android Auto and connected to our mobile phone via a USB cable. The whole system will be mounted inside of a builders toolbox, this lets us transport it safely and acts as a nice harness to encompass everything … sounds simple enough, right? Lets do it.

## Gather the parts

There are a few ways to set out your stand, we opted for a light up switch for the power, this actually made the build slightly more complicated as we had to work out how to connect three wires instead of the regular two on a simple switch. We also opted for a big (10 amp) power converter, this was on the recommendation that the Pioneer headunit ran at about ±5.2 amps. While a smaller one should work fine, we opted to stay on the safe side.

* 1 x [Toolbox](
* 1 x [Acrylic sheet](
* 1 x [Android Auto headunit](
* 1 x [Headunit-to-wires connecter](
* 2 x [Speakers](
* 2 x [Switches (power & handbrake)](
* 1 x [Cigarette power converter](
* 1 x [Power converter](
* 2 x Hinges
* 2 x Brackets
* 1 x [Sticky-back velcro strap](

Then you need a load of [wire]( to connect the power up (our speakers came with audio wire). Here we also opted for thicker wire than was probably necessary but it allowed greater flexibility to pull and bend. The downside was when we wanted to put two wires onto one switch, the twisted pair was very thick and so it was hard to thread through other clamps.


## Gather the tools

We used so many tools! This was not predicted before the build was started. I would recommend to make sure you have a full compliment or know someone who has such things as, wire strippers, pliers, tweezer pliers, bremmle drill, file, hand drill, wire tape and wire connectors.

We also used a laser cutter at [DoES Liverpool hacker space]( to cut out the acrylic sheet, engraving the Novoda logo and the bugdroids you can see on the finished product. Watch out when creating CAD (computer aided design) designs they may look wonderful on your own computer but when transferred to the actual laser cutter it’s a whole different ballgame. This is because CAD files uses weigh-points to distinguish where to cut and each version of the software (including across mac / windows) have a different perception of how weigh-points work. Many hours spent back and forth here.

## Understand the wiring

Side note: The handbrake (parking brake for you Americans) on a car determines whether you can type text and do other functions on a car headunit. When the handbrake is on, the head unit assumes the car is stationary and so allows keyboard input. Since we are not a car we will be attaching the handbrake to a switch.


Electronics are not our forte I must say. However let me try and explain. Car batteries have ground ( – ) and live ( + ), connecting a device with these gives you power. Switches with built in LED’s need this circuit also. The cigarette power converter has two wires ground and live. The power of the Pioneer head unit has power and ground. The handbrake only needs ground.

Therefore to turn our demo unit on and off, one of our switches has ground from the power supply and ground from the head unit into the ground terminal. It then has live from the power supply into its power terminal and live from the headunit into the accessory (acc) terminal. This allows the light to come on on the switch as we turn the head unit on.

For the handbrake to complete that circuit you have to connect the power supply ground to the green handbrake cable. Unfortunately we couldn’t work out how to get the light to come on when the handbrake was on without shorting out the whole box, so there is no light on the handbrake.

Audio wiring is simpler: it’s plus to plus, minus to minus. Make sure you keep as much audio cable bundled up in a cable tie so as to later avoid cable entanglement hell.


## Measure it all

“Measure twice cut once” is the mantra. I recommend measuring four or five times!

Here we first measure the size of the box so we could order the correct size acrylic perspex for the top. Pro tip: if you’re doing this on a CAD machine, allow extra space on all sides for a margin of error because it’s actually really hard to know exactly where the laser cutter is pointing. Our speakers were four inches in diameter so we traced two circles for them either side of the head unit. This was ordered as a custom piece of perspex from Sign Materials Direct.

Measure your headunit—note that these come in a caddy designed for you to easily fit it into your car, this can be removed before you measure. Another thing to measure is the amount of cable you will need, we added extra slack as we were not sure whereabouts in the box the switches and battery would sit compared to each other.

Something we didn’t do but should have: measure where the hinges, headunit braces and speakers are going to go and add these to your CAD designs. This stops you going back later on and having to drill the plastic (each time hoping you don’t crack it).

## Connect the bits

Connecting it all together allowed us to test the full system before we put it into the box. Connecting the switches allowed us to test the handbrake was working. If you go onto Google maps when the car is in motion you will not be able to search via the keyboard.


## Design fascia

We added some flair to the fascia by engraving Android logos and also positioning the switches in between the “O”s of our company logo.


## Install into fascia

Using nuts and bolts we attached the speakers to the perspex, then the head unit with brackets, nuts and bolts to the perspex. The switches already had a screw mechanism that fit nicely through our holes. Thing to note here: the Pioneer head unit comes with its own plastic surround. You can use this to hide any ‘mishaps’ from your cutting. One thing to keep in mind is that it has little nodules on it that you have to account for when cutting your rectangle (or you’ll need to file them out afterwards like we did—oops).


## Install into box

Adding the hinges is what you need to do here. Pro tip: remove the speakers and pioneer head unit from the perspex before you line up the hinges and attach them. This allows you make sure you have an flat surface to get the contact correct. We also had some sticky back velcro so that we could attach the power supply to the bottom of the box. Don’t forget to drill a hole out of the side so you can hide the power lead when displaying your amazing Android Auto demo unit.


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