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Ideas for a new project. PIC and car radio AMP

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mramos1

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I bought my son a used car and we put in a new setero (one with an input earphone jack he can plug his MP3 player in). He was telling me it had a click or something. I went to listen. Turns out the preamp on the input jack/MP3 on the radio does not have enough gain. It is a cheap no name brand but it had SD, USB and the input jack on the front of it.

I do not want to open the radio (as it is installed and a pain to get it out).

My thought. I have an amp I can put in the trunk and there is a large wire I traced it to the battery (was shocked it had a fuse). Frame is ground. But they did not run an ignition wire to the radio area.

The AMP needs that to turn it on. If I jumper that, the amp is always on.

My thought.. I small board in the trunk that taps one of the incoming speaker wires (now an amp input) to an opto going to a pic (16F683) running 31Khz (low power). Using the pic ADC via the opto. If the PIC sees audio I know the radio is on, I power a transistor and realy to power the AMP (power/ignition).

Anyone have a better idea? Simpler is fine.
 
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If the car radio is loud enough when you use the tuner/CD, then you don't need a power amp. You need a small pre-amp between the MP3 player and the input earphone jack.

Anyone have a better idea? Simpler is fine.
Run a wire to the fuse panel and tap into a circuit that is ignition switched. ;)
Or, if your power wire powers nothing else than the amp, then put a relay in the line where it taps into the cars power system. Control this relay from a ignition switched source.
 
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Correct, the right fix is a preamp, but he did not want more items on the console as this radio was to rid him of the Belkin FM transmitter and make things cleaner.

I found power in the trunk (contant power) and figured I would add it and let him push more sound in the rear.

Maybe I will look at a preamp and hide it somewhere. What is sad is the work to pull the radio again and then to open a new radio to probably change 2 resistors if I had the schematics.

Oh well. He will have to live with it. As a child I recall worse things. :)
 
mramos1 said:
I bought my son a used car and we put in a new setero (one with an input earphone jack he can plug his MP3 player in). He was telling me it had a click or something. I went to listen. Turns out the preamp on the input jack/MP3 on the radio does not have enough gain. It is a cheap no name brand but it had SD, USB and the input jack on the front of it.

I do not want to open the radio (as it is installed and a pain to get it out).

My thought. I have an amp I can put in the trunk and there is a large wire I traced it to the battery (was shocked it had a fuse). Frame is ground. But they did not run an ignition wire to the radio area.

The AMP needs that to turn it on. If I jumper that, the amp is always on.

My thought.. I small board in the trunk that taps one of the incoming speaker wires (now an amp input) to an opto going to a pic (16F683) running 31Khz (low power). Using the pic ADC via the opto. If the PIC sees audio I know the radio is on, I power a transistor and realy to power the AMP (power/ignition).

Anyone have a better idea? Simpler is fine.
U are talking about a 12F683? Don't realy need a ADC for that. Just a PIC with internal comparator like 12F629. Rectify a part of the audio signal (u can use a transformer for better insulation). Just be careful about the voltage limits for PIC's imput (use a voltage divider or a diode in series with a resistor ev).
Even simple ...a opamp with a low voltage ref and a 1 transistor amplifyer for the rectified signal.
 
Tarsil.

Not a bad idea. A transformer, output thru a I diode into an opamp and a voltage divider on the - side. There is probably some voltage when the radio is on (no matter how high the volume is) to force the opamp high.. And a transistor to the relay. That should do it.
 
Hmmmm.... Another thought. Most car radio audio stages are a bridge output; ie: the outputs are biased at 1/2 the supply voltage when the radio is on. Use this 6-8Vdc signal to turn on a relay via a transistor. You may need a diode and cap to keep the transistor on between peaks in the audio waveform at full volume.
 
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