Need help on getting started with React Carplay

Carplay Support
1

Hello Rhys/All!
I have very some basic knowledge in programming and electronics and I love retrofitting new tech to older cars but I’m new to Raspberry Pi and have zero knowledge on it.
I want to know more about some details about it before I fully commit on the React CarPlay project (even though I already gathered almost all things required for it :slight_smile: ).

Car in question is a 2005 Citroen C4 Coupe VTS with factory Magneti Marelli - PSA RT3 headunit (in some markets called ‘NaviDrive’). It is featuring relatively big hi-res TFT screen for its era and would look great to be retrofitted with CarPlay with physical controls over steering wheel or buttons on the unit.

Screenshot 2025-03-06 060639
Screenshot 2025-03-06 060639720×662 107 KB

However, there is a slight issue… There is a RCA input in the glovebox and a Video mode which can be turned on in the menu - but the limitation is that the unit switches back to navi mode when you start moving – going over 15km/h. There is no option to code the BSI (Main Body Module / ECU) to remove this limitation with the OEM diagnostics equipment (DiagBox/Lexia) nor with any alternate methods - there just aren’t people fiddling with these cars and equipment so nobody so far has found and posted a solution to this problem on software level.
There is a not-so-elegant workaround which most people used for retrofitting reversing cameras, they would hardwire a switch to the display’s contacts on the ribbon cable thus bypassing the driving-cutoff of Video mode but that makes more problems.
When hardwired, the screen will play the content directly from the RCA input which is great but the steering and headunit controls would still work in the background and thus by using them you’d be moving thru navi Ui menus and maybe even unwillingly change something in the background.

So, question is: Does Raspberry need some CAN expansion board or can it natively be able to read and maybe emulate CAN messages? If so, I guess it would not be hard to send a CAN message to headunit to make it think the car is stationary?
Also, the same question applies for the Steering Wheel controls.

I would like to start from there as the whole project depends if this workaround could be implemented.

Thank you very much in advance for help!

2

It all depends on how it’s working. I suspect that there is a canbus message that triggers this display switch over. It could either be the speed is sent directly to the display, and the display switches when it receives a value over the trigger speed, or it maybe be a simple Boolean value of a zero or a one when the screens enabled/disabled. If this was me, I would look into making what I call a canbus proxy. You need this because canbus messages aren’t generally sent once, but repeatedly ever x milliseconds.

A proxy would allow you to relay all messages to and from the screen as per normal, but override the specific trigger one.

Again this is all dependant on whether canbus is the actual trigger!

A pi doesn’t handle canbus natively, it requires a relatively cheap canbus board.

Thanks

Rhys

3

Thank you very much for replying and for info Rhys, highly appreciated!
I’ve managed to find some CAN info for PSA cars (https://autowp.github.io) and now it’s just up to me to learn how to do progress from here :slight_smile:

The CAN data on pretty much all PSA cars should be quite similar as they share a margin of modules and devices between them and I see that there is a Alert message “10 km/h!” which displays the fasten seatbelts message on display and also uses it for self locking if it is enabled in the car, I have a suspicion it’s the same trigger as for Video cut-off - now just to find the origin of the trigger.