I want to make reactive LED strip for my car and I want to make it somehow smart... I figured a schematic like the one below:
The LED has a 12 V source at the beginning of course. KEY3 is a relay but the case we are considering here doesn't matter, because it's closed
I connected the circuit as shown below but it doesn't work as expected. The LEDs are lit when the radio is on but the volume is zero. I checked the voltage on the speaker wire and it shows about 6 V when the radio is on, and near to 0 V when the radio is off. But I measured it with DC voltmeter.
I know speakers work on audio signal between two terminals, which is basically an AC signal, but I thought connecting the base to one speaker wire would create pulses of voltage between the base and the emitter. Instead, the LEDs are on all the time. When I turn up the volume they seem to start pulsating but they are never really off.
The ground shown on the schematic is the cars mass ground, so it isn't connected to the speaker in any way.
Unfortunately, I don't have an oscilloscope to look at the speaker wire signal.
Is there any way I can connect it so that the LEDs flash to the music?