Been wanting to do this post for awhile now. It's been a combination of research and a lot of testing to get to this point. Quite pleased with the outcome but would like to make some changes later on, more on that later.
A few goals I had for this project:
- Delete radio/head-unit.
- Keep everything as simple as possible, think minimal.
- Nexus 7 tablet to display all the Megasquirt gauges via Bluetooth.
- GPS with offline maps, pause/resume music on power off/on, wired tether to phone.
- Maintain charge with full brightness, GPS, music and gauges running.
- Easy to remove tablet from the car, one cable to dock.
- Amplifier install that is compact yet has tone controls (bass/treble).
To make it possible for the tablet to dock with just the one cable (USB), and not have to plug the headphone/Auxilary cable in as well, I had to use the tablet's USB OTG Host feature. This basically allows you to plug heaps of USB devices to your Android device, keyboards, mice, thumb-drives, USB DAC, etc...
However, while in OTG Host mode Android doesn't allow the tablet to be charged at the same time. This is where the software comes in to make it all possible. Check out Timur's website for details on his custom built ROM. It is optimised for car installs and enables charging while in USB OTG Host mode, deep sleep mode when power loss is detected (huge power saver), and hot-plugging of audio devices.
You will also need a USB OTG Y-Split cable, I picked up mine off eBay for not much money. While you're there you'll also need a USB DAC, again very little money for these. The USB DAC basically plugs into the tablet via USB and outputs sound for the amplifier.
We're very lucky with Megasquirt when it comes to Android software. MSDroid allows tuning as well as gauges, still in the beta with a new major release soon. ShadowDash is by the same creators as TunerStudio and is a lot more stable but only allows gauges and no tuning features.
For amplification, I decided to go the DIY route. This consists of a pre-amp so that I could have bass and treble control. For the power-amp stage I picked a DIY kit that is built around a IC chip that is commonly used in car radio.
Took me literally under ten minutes to build the power-amp, pre-amp took a bit longer. I than stuffed them both into a plastic case with the USB DAC. The case was picked up from JayCar.
Sound wise, this combo worked very well. The pre-amp gave me plenty of tone adjustments and power-amp was able to keep up with the volume levels I usually listen at. But it did suffer from a "pop" noise on power up, and I may have blown the IC chip because of insufficient heat-sinking!
So the other option I'm look at is this little amplifier, Pyle PLMRMP1B. It's very compact, plenty of power, remote gain control and anti-thump turn on. I'll re-use my current DIY pre-amp though, need those tone controls!
My initial install of the tablet wasn't very successful. Couldn't use my hazard/retractor buttons without removing the tablet, very flimsy, and blocked both centre vents.
I than found a company called ProClip that produce a Nexus 7 holder that was perfect for my requirements.
I used a custom made radio panel, available through my store, and made it a complete blank. This would allow me to hard mount the ProClip tablet holder. Very happy with the qualilty from the holder, sturdy and easy to dock/undock from the car.
For the wiring part, I used new connectors. 4-way connector for the outputs to the speakers, and a 3-way connector for ground, accessory and constant 12V power.
Photos of the finished project!
- Nexus 7 Tablet - $120
- Centre console delete kit - $100
- Stainless steel radio blanking plate - $95
- ProClip Nexus 7 holder - $80
- USB DAC - $14
- Serial to Bluetooth module - $12
- Amplifier TDA7377 - $12
- Pre-amplifier LM1036 - $11
- Narva 4-way connector - $6
- Narva 3-way connector - $5
- USB OTG Y-split charge cable - $5
- Plastic case - $5
- USB car charger - $4