DTMF on a 12V car system

Hi,

Does anyone have a smart solution how to add a DTMF signal to a part if a car's 12V system. I have a device that I will control using DTMF but I can not install extra cables. It is powered from the car battery/generator and will draw up to 10A so I planned to use the same cables for both data and power supply. I would like to get 100-200 mV p-p for the DTMF signal on top of the 12-15V DC level. The DTMF signal is generated from a PIC with 5V supply.


best regards

me

Something like this was talked about a few months ago. Maybe it will give you an idea? Have not done this myself, so not much help from me.

If the DTMF at the source was changed to a digital signal, and the receiving end would change the digital to one of the DTMF frequency?

http://www.picbasic.co.uk/forum/showthread.php?t=9568
There are links in the thread to other threads about the same subject.