Important: Microphone polarity

[Faraaz VK4JJ]

This post is to stress to you the importance of installing your microphone in the correct way.

Manuel, Dl2MAN, draws attention to this in his video.

I have learnt the hard way of what happens if you do not do this (approximately seven hours of troubleshooting, reworking microprocessors with hot air etc) - learn from my mistakes.

The microphone is tiny, approximately 5mm in diameter. There are two pins. One pin is ground and this is tied to the metal housing. You must take the utmost care in probing between the housing and the pins, preferably using a fine multimeter probe, to determine which is ground. Mark the ground pin with a black marker pen.

Install carefully and solder into board. Remember, square-shaped through-holes on the board are ground. This will help you locate the microphone.


If you do not install the microphone correctly, you will have no transmit audio on SSB (obviously) and you will also not have access to the ISP programming. This is because MISO is shorted to ground through the incorrectly placed microphone and will be invisible to the programming computer.

Manuel also suggests as a troubleshooting measure, to insert a plain 3.5mm jack into the mic/key socket without any cabling. If you are able to program the microcontroller with this in place and you couldn't before, you know it is a mic issue.

[DL2MAN]

I might add to this:
If you managed to program your Rig before, and inserted mic after programming with reversed polarity, and you switch it to CW and enable Keyer, it will start to transmit a series of DAH´s..... That´s also a sign of a reversed mic.

73 Manuel; DL2MAN