DIY Microphone with PTT Switch for µSDX

October 5, 2021

Actually making a DIY microphone with PTT switch is a relatively easy project. All you need are;

  1. 1 x Electret Microphone
  2. 1 x 10nF Polyester Capacitor
  3. 1 x Momentary Switch (normally open)
  4. 1 x Box mountable headphone jack
  5. 1 x Project box
  6. 1 x Regular aux cable
  7. Misc. cable
  8. Misc. drill bits
  9. Soldering iron
  10. Solder

Looking at the schematic of µSDX, the ring contact (number 3 in the schematic below) of the male 3.5mm plug connects to the PB4 pin of the Atmega 328p.


In order to trigger the PTT functionality of the µSDX, the pin 3 needs to be connected to the ground connection via a momentary switch. However, directly connecting the electret microphone to the µSDX is not recommended and therefore a filtering capacitor needs to be added between the + and – pins of the microphone. The schematic is follows;














The pins should be connected to the mountable headphone jack with the following order;

  • Mic – to the Pin 1 of the jack
  • Mic + to the Pin 2 of the jack
  • PTT to the Pin 3 of the jack

If all is done correctly, you have completed the circuitry needed for the function of the microphone. However, leaving the electronics naked is never a good idea. I have bought a 35 x 50 x 15mm project box and drilled two holes for mounting the headphone jack and PTT button. I have also drilled 4 tiny holes in the box where the electret microphone lays behind. The finished product looks like this:

I hope this mini project was helpful. Stay safe, 73.