"Mike McAuley" wrote in message
ink.net...
Hello,

I have four radios in my vehicle, all with remote speakers (unpowered)
that are fairly close to each other. It's confusing sometimes when
squelch breaks, to identify which radio is active.

I'm wondering if there is a way to rig a circuit, so that a small LED
light can be inserted into the speaker wires somehow, so that the
light illuminates when the speaker is active.

Thanks for any help,

Mike
Tucson, AZ


I'm just going to throw this out for thought....

Try using an audio transformer as a current transformer into a
high-efficiency LED. Break the wire to the speaker and insert the low
impedance winding of the transformer in series. Connect the LED to the high
impedance winding with an anti-parallel diode (1N4004, say). Use maybe a
10:1 turns ratio transformer (100:1 impedance ratio) from Mouser, Digikey,
or Radio Shack.

If one assumes 50 mW output power into 8 Ohms, that is about 80 mA of
current to the speaker. The transformer makes it about 4 mA into the LED
(the 1N4004 conducts in the opposite direction). I think 50 mW is a very low
estimate for the amount of audio you need in an auto. If the LED burns out,
use a higher turns ratio transformer.

The LED will flicker with the audio. The louder the audio, the less flicker
and the brighter the LED. Conversely, if the volume is low enough, the LED
will barely flicker and be mostly off.

Anyway, just an idea.

Good luck.

John
KD5YI