Originally Posted by durwood
I completely missed the "for a transmission" part. :lol:
In that case, then just invert it either with a transistor or use the other pins on the relay for NC instead of NO.
Not too bad.
Again, I have never done this, or know how well it would work. It might induce quite a bit of noise to the system, or stare WWIII, I dunno.
the only thing he didn't say was if he has his audio running through amps or the HU? If he has aux in or the amps, then he would have to build some relays to switch the RCA audio signal back and forth. If there is no aux in or no amps, I don't know what his "transmission" will play over. :confused: I don't think it would start WWIII but maybe send signasl into space like Contact :lol:
Guess something like this should do the job...
the signal sent over the rca cables is not AC. AC by definition passes through zero. This is more of a fluctuating DC, like an AC signal already riding a DC bias. A rectifier does no good there, as the signal doesn't pass through zero. What about an inverting, comparator op amp. This would give high input impedance, as seen by the scanner, could bump up the signal to a desired level to keep the mute off when wanted. Filter it's output for noise and to keep the opamp from turning on the mute function erroneously.
Well the rectifier will make sure that the signal is going the right way. Without the rectifier, if you connect the wires backwards, it will not work. So for like $0.04 in diodes, you get the lazy man's circuit. :D
Originally Posted by h3rk
If what h3rk said about the the RCA line not containing AC is correct an op amp set up as a comparator is the way to go. In this setup the op amp will effectively form the rectifier, peak detector and amplifier functions for you. The only problem i can see with the idea is that the op amp wont output a proper ground when you want it to if you use a OV source on on of the op amps supply pins. You'll actually get 1V or 2V. If this is enough to mute the head-unit then fine. If not you'll need to use around -1 or -2V supply voltage to get an output of 0V. You could use a potentiometer to adjust it to get exactly 0V output.
The risk here is that you could potentially output a negative voltage to the head unit and I don't know what side effects that may have.