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2-way radio headset microphone....?
2-way radio headset microphone....?
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Old 21st June 2011, 01:16 PM   #1
Ramrod is offline Ramrod  United States
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Join Date: May 2011
Default 2-way radio headset microphone....?

Im trying to make my own headset for a motorcycle helmet so that it will work with a motorola 2-way radio among other things.

Im a little confused about the microphone wiring. The motorola radio has a 2.5mm stereo jack with the speaker signal on the tip, microphone input on the ring, and ground on the sleeve. I bought a cheap hands free set for the radio that had a mono earbud and a mic with push to talk button, made by motorola. I took it apart and there is a board with a capacitor and resistor in a circuit with what appears to be an electret mic capsule.

How does this work with only a ground and one other connection to the radio? is it actually a dynamic mic if so what is the cap and resistor for? How can i tell?

The mic signal ring on the radio connector is outputting like 3.5VDC. I did hook up a dynamic mic element to the mic ring from the radio in series with a NO pushbotton to ground as a PTT, and when the PB was depressed it worked fine. I would like to use an electret mic since noise cancelling ones are cheap and readily available.

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Old 21st June 2011, 03:36 PM   #2
Ramrod is offline Ramrod  United States
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So this circuit must have the audio signal from the mic and the power supply for the electret combined into one line (phantom power?) not too familiar with mic circuits. The RC circuit on the board must be a filter....?
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Old 21st June 2011, 04:17 PM   #3
Frank Berry is offline Frank Berry  United States
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The cap and resistor are designed to keep the 3.5 volts away from the dynamic mic element. The resistor is probably there to bleed off the 3.5 volts across the capacitor when the mic is disconnected from the radio.
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Old 21st June 2011, 07:32 PM   #4
Ramrod is offline Ramrod  United States
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Join Date: May 2011
If it were a dynamic mic why the radio output 3.5VDC on the signal input? Or do you actually think it is an electret element?

Sorry if im an idiot.
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