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[aprssig] Mic-E and HTs

Ian ZL1VFO zl1vfo at yahoo.co.uk
Wed Dec 14 10:54:28 UTC 2005

> Works the same way, but in addition to the diode
> bypass from the PTT input to the PIC to the PTT
> output from the pic, you just add a capacitor too.
> Ill draw it...

> See http://www.ew.usna.edu/~bruninga/mic-ePTT.GIF

> de WB4APR, Bob

Just had a quick look at the circuit above, and two thoughts spring to
mind (not a criticism or anything, just working out what might

If one just placed the PTT switch in series with the electret mic, you
could probably do away with the 2k2 resistor, assuming the mic still
drew sufficient current to trigger the radio PTT circuit.

...and, if current were flowing through the diode shown there (PTT
pressed), the diode would essentially be turned on, and so the mic
audio should get past it ok without the need the extra capacitor.


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