Hi,

I was just wondering how exactly do the TEL inputs work on the VW radios such as the VW MFD?

Is it simply a case of sending analogue audio to the TEL +/- pins and at the same time grounding the TEL MUTE pin in order to interrupt the current FM radio playback? Have I got the wrong idea about the TEL MUTE pin? If I'm right about the TEL +/- pins, what is the maximum voltage I should be supplying to the TEL +?

I'm asking because I have an idea for an arduino device which would provide Bluetooth functionality to my old car in a "factory" way. I know there are devices which plug into the CD inputs of the radio, but they require you to switch to CD in order to use the Bluetooth input to the radio. What I want is a method which will interrupt the current FM radio playback when Bluetooth audio/calls are received rather than having to be on the CD input source in the first place. Also in future I plan to extend the arduino functionality to provide caller ID and song information to the FIS LCD display in the instrument cluster.

Thanks,
James

Thanks for your reply, but unfortunately my car is a 2000 reg and so there is no factory option available which I can retrofit. I know how I can send the caller ID to the FIS LCD display once I have it, as luckily there's many people who have managed to write text to the FIS using an arduino.

All I need to figure out is how the TEL inputs to the radio work such that I can pass the call audio through the car speakers whilst at the same time interrupting and muting the current FM radio playback.

So far I have decided I will use the Sparkfun Purpletooth Jamboree: https://www.sparkfun.com/products/11924

With that I can pair the phone to the Arduino using Bluetooth and I will use two audio outputs:

I will use the mono line out to the TEL+/- pins which will provide audio to the radio on an incoming call, whilst at the same time one of the arduino pins will activate a switch to ground the TEL MUTE radio pin in order to interrupt any current playback.

The second audio output is used when performing Bluetooth streaming of music/audio and will use the stereo line out to the CD L/R pins of the radio in order to provide higher quality audio when listening to music from the phone. This second output will require switching to the CD mode but that's fine as CD will just become BT Audio, but the BT call interrupt will occur regardless of what input is selected on the radio (so there is no requirement to be on CD mode for BT calling).

That's what I have so far