Steering Wheel Interface for Pioneer Radios

I'm going about creating a steering wheel interface for those of you with Pioneer radios that have the wired remote input.

This is the information about the wired remote:

http://jvde.net/node/7

Here are the resistances you get from the audio controls on the wheel (tested, but these are also from the service manual). Measure between pins 1 and 2 on the audio control pad itself:

71 kOhms = Nothing Pressed
270 Ohms = MODE
740 Ohms = CH UP
1.3 kOhms = CH DOWN
2.1 kOhms = VOL UP
3.1 kOhms = VOL DOWN
4.6 kOhms = SPEECH
6.3 kOhms = OFF HOOK
8.6 kOhms = ON HOOK

They are supposedly routed to the radio on pins 2 and 12 of the main audio harness, but I have not tested that. The service manual does indicate they arrive unmolested there.

I have attached the circuit I plan to build. Sorry for the extremely ugly diagram, I've never used kicad before so... uhhh... still learning. ;) I'll let you all know how well it does or does not work. And I'll add in any significant changes I make (you can set your own choice of output resistors to do any radio functions you like).

As far as I can tell, this should work for any Pioneer stereo that has a 3.5" headphone jack labelled "W/R".

Attachment 11140

Very interesting project!

I hope you don't mind, but I posted a image of your schematic. Its kind of hard to read, but should give the general idea. People can grab the PDF if they require more info.

Thanks! Didn't think of that. Once I finish it up I'll post the actual kicad files so they're editable, too.

So, for those trying this out, the circuit didn't work as pictured for me. I'm working on some improvements that should get it going. We'll see how it turns out. One good thing is that the voltage divider setup I created for the buttons worked exactly as expected (One note: The buttons show 71 kOhms when nothing is pushed). Pins 2 and 12 were the correct pins after all on the head unit connector (REM+ and REM-). I connected ground to REM-. Pin 2 is pink, pin 12 is violet.

My plan is to replace the 2.2 kOhm resistor for the wheel with a 5k multi-turn trimpot. That should give me the adjustability I need to "dial in" the wheel controls. Failing that, I'll replace the two resistors adjusting the current/voltage for the IC with appropriate trimpots to dial in the voltage. Part of the issue is that in the real world getting everything exactly perfect doesn't happen. My expected voltage was 7.71 volts, but it is actually 7.5. Also, the voltages on the voltage divider for the buttons are off. That results in the wrong relays being triggered, and multiple buttons being mapped to the same relay.

Hopefully in the next week or two I'll get this ugly prototype working. Once that's done, I'll update the schematic, give some more useful instructions, and I plan to design a proper printed circuit board so this can be easily replicated. I'm of the opinion now, though, that at least one trimpot will be required to be custom adjusted to your specific situation when you install, but if it can be kept to just one, it shouldn't be too hard to do.

Yes, for those who love microcontrollers, this would be WAY easier with an arduino. Like 100x easier. Maybe even easier than that. But then it would cost more and wouldn't be as fun as doing it the 100% analog way. ;) Plus it would up the parts count to many times more than you see here, necessitating you to buy a pre-made arduino board rather than just having the entire thing custom.

BTW: I did a couple of basic tests on the head unit already and it does accept button "presses" as advertised on that site. So that's encouraging.

Would it be possible to fix your issue with tighter tolerance resistors? I can see that the tolerance stack up would become an issue with that many resistors in series.

Great work btw!

Pretty close now. Replaced the 3.74k resistor with a 10k trimpot and adjusted the voltage on pin 7 and 6 with it until it was exactly 7.71 volts. Also bridged L3 and L4 (moved L4 - L8 to L5 - L9). Now all the buttons are working perfectly except answer and hangup. Nearly there... surprised voice control worked without a hitch.

Alright, all finished. Everything works 100%. All buttons do what I wanted them to do (I actually set my mode button to be mute, I find that function more useful on the wheel). Now I just need to build one that doesn't fall apart and look like crap. :P Answer and hangup are reversed but that's just a wiring issue. Those two didn't work before because I wired the resistors to the wrong relays.

Note: Don't try to cram all this on too small of a circuit board. It just makes the job 100x harder.