building my own aux circuit car stereo feedback


Posted on Feb 6, 2014

By looking at the layout of the PC board, decided to insert a stereo 3mm canceling type jack (5 pin) at the volume control chip inputs, and mounted it on the front panel. Did not find such type of jack in my parts bins, and canibalized one out of a old PC sound card. Works well, simple, and does not need relays, transformers or sensing circuits. When the plug is removed, the radio plays its source normally.


building my own aux circuit car stereo feedback
Click here to download the full size of the above Circuit.

When inserting the plug, only the portable gadget feeds its audio source. It sounds much better than the FM modulator we tried before. With the detection part of the circuit, I`m simply holding the transistor "ON" with the 10k resistor, then looking for a path to ground through either L or R inputs via the 3. 3k resistor network. It seemed to work fine on the bench; the relay was held "ON" and when I connected an audio source, the relay switched off. I added the 3. 3uF caps to keep the input detection part from "buzzing" the relay when it sensed the ground on the input side of the isolation transformers. Do you have any suggestions to improve my circuit Should I add some shunting resistors or decoupling caps to the stereo side to soften the connect/disconnect Isolation transformers are used to isolate grounds, but your grounds are connected together. Even if you had separate grounds, the noise will pass through the transformers. With the detection part of the circuit, I`m simply holding the transistor "ON" with the 10k resistor, then looking for a path to ground through either L or R inputs via the 3. 3k resistor network. It seemed to work fine on the bench; the relay was held "ON" and when I connected an audio source, the relay switched off. I added the 3. 3uF caps to keep the input detection part from "buzzing" the relay when it sensed the ground on the input side of the isolation transformers. Last weekend my daughter...




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