Raspberry Pi Car Shield

Raspberry Pi 2 + Power supply PCB + 7″ TFT

I’ve had an aftermarket ECU (Adaptronic) in my car for a little while now, and I wanted some extra dash gauges. My car (Nissan R34 GTT) has a spot on the dashboard perfect for a 7″ TFT. Raspberry Pi is the obvious choice, However, you can’t just run a Pi directly off the accessory power in a car. Aside from voltage conversion, graceful shutdown is also mandatory!

Custom PCB time

The first problem with putting a Raspberry Pi in the car is power. Yanking the power out suddenly will corrupt your Pi. Secondly, a car’s electrical system is 12V and the Pi needs 5V. Lastly, the Pi has a serial port on it but it’s TTL. I needed true RS232. Time to build a custom circuit board!

RPI-CS

I’ve called my custom board the RPI-CS – CS = Car shield. What does this let you do?

Convert 12V to 5V for powering the Pi
Graceful shutdown
GPIO inputs for changing functions on screen
RS232 port
RTC (Real Time Clock – the Pi can’t tell the time on its own!)

Pictured below is my first revision PCB sitting on top of the Pi. This PCB converts the car’s 12V down to the 5V needed by the Pi, and also controls the sequencing required to gracefully shut down the Pi when the ignition is switched off. A GPIO line informs the Pi when it’s time to shut down, and after some time the PSU automatically switches off (the standby consumption is microamps so it will never flatten your battery!).

The PCB also converts the TTL serial to RS232 (for the ECU), and provides some pushbuttons to control the Pi (I cheaped out and bought a non-touch TFT). The TFT itself is LVDS and comes with a converter board that takes HDMI from the Pi.

Currently the display runs a Python script to poll the ECU and display gauge data.

Eagle-eyes will spot a GPS module, this has been removed since I can buy a USB GPS for less cost than a solderable module (crazy!). The USB one works natively with gpsd so why reinvent the wheel!

The Pi also can be made to tether to a phone, so a future project will be integrating the Pi’s audio output to my car stereo. I can then plug my phone in and stream internet radio to my car speakers 🙂