I have several Zetron DTMF microphones.  These are great little mics, used the heck out of them in the 1990’s.  But today I can’t find any information on them.  I really need a pinout for them so I can figure out how to wire them up to various radios.  Here is what little I do know.  If anyone can contribute more I would really appreciate it and will add it to this page to help others.


Zetron ZMX DTMF Microphone

Access programming mode by holding down the 1, 2 and 3 keys as you apply power to the mic.  Release the keys once powered and you will hear a series of beeps indicating you have accessed programming mode.

Initialization to factory defaults is 80#

Write the program to memory with 52#

Exit programming mode with 0#


When you open up the mic and lay the front of the mic (with the digits) face down on your bench you will see the connector for the mic cord.  Let’s say that connector is on the “bottom” of the board.  There are six pins there and on the one I’m looking at only five are used.  From left to right this is what I’ve figured out, with pin 1 being the left most pin:

  1. No Connection
  2. Blue wire, microphone hangup, open collector switch.
  3. White wire, TX audio (mic and DTMF) with 2 Vdc voltage on it.
  4. Black wire, DC ground
  5. Audio ground?
  6. Power

Mine seems to like +12 Vdc for power.  I’m guessing that JP6 would change that but I’m not sure to what (read on for more).  I am reading about 2 Vdc on the white wire at all times.  When I press a DTMF button I get about 170 mVac on that wire so that’s why I assume it is TX audio.

Notice that the back of the microphone has a black wire on a connector.  I know for a fact that this is supposed to tell the radio that the mic is hung up.  It does this because you ground the microphone hangar and when the mic is hung up that ground makes connection.  Hams might not use this.  In commercial radios it’s handy to pause scan when the mic is picked up.  Or to defeat CTCSS so you can monitor the channel (a legal requirement).  In this mic it appears to activate a transistor switch and the blue wire is on the open collector of that switch.  No voltage here from the mic.


This would be a good time to explain how I am assuming the jumpers work.  A little bit “above” that connector is a header with two rows of pins, 6 pins in each row.  There are jumpers on mine that are across the left most pins, row one to row two.  The next pair is vacant.  I believe this is JP6 because if I remove it and apply power the mic does not power up.  So I then assume the next position, currently vacant, would be whatever power option is available (maybe like +5 or +8 Vdc?).  If that’s true, and that’s “if”, then we can assume the next two are JP4 and the final pairs would be JP3.  Zetron can be funky like that so it may be right.   Here is what I’m told about the jumpers:

Internal jumpers:  JP3 is for flat/pre audio out.  JP4 is impedance selection.  JP6 is external power selection.