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I would like to make a red led circuit that plugs into the headphone jack. I want to replace the detector tone with a red light. I don't know what value of resistor or potentiometer to experiment with?
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You can try it the simple way but this might not work or give good enough results:
connect some ultra-bright LED in series with a 50 to 200 ohm resistor and
both wire ends with the audio plug (solder the ends vice versa to the plug if you see nothing)
Mainly it depends on how high is the output energy level for the headphone.
If its just a few mA you may see nothing or just a very dim light in dark surroundings.
More professional would be if you create a little amp-stage with 1 transistor so
the LED will gets switched to full on via a main-LED-battery-circuit
if the audio signal hits the transistors base. In such case you need at least
2 to 3 small button cells to provide enough voltage for the LED, a single 1.5v battery is not enough.
Or you can use the detectors voltage with some extra cable and plug.
The second method is recommended because you will need a pretty bright LED output
so you will see it not just at night. Its also much better that way so you can adjust it
from at what signal-volume-level the LED will shine directly full and not flickering all the time
which may give you the impression the find signal is always on.
btw. a very comfortable method of silent detection you can get with the new Makro Racer:
The display background LED light will go on (for ca. 5 sec) or the vibration if it was set to it,
even both of those alerts at the same time is possible.
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