Icom HM-151 microphone data mute mod

I found the design of the Icom HM-151 lacking in that it did not mute the microphone when running data modes through my SignaLink.  The solution is simple.  Install a tiny relay so that the microphone element is only connected to the radio when the PTT button on the handheld mic is pressed.

The tiny relay I found was actually Double Pole Double Throw.
NEC Miniature Non Latching DPDT Relay 5V 1A SMD SMT EB2-5NF

The specifications were quite impressive and the relay coil draw is very low, which is ideal for powering from the little Q1 pass transistor in the mic.

It was easily tacked into the circuit.  First the mic trace on the board had to be cut off.  I did this with an engraving tool.  See the X on the board where the trace was ground away.

The Common (Pin 8) and Normally Open (Pin 7) relay contacts were soldered directly to the board to reduce lead length.  The un-used pins were bent carefully out of the way.

The coil minus lead (Pin 1) was soldered to the PTT button contact.
The coil plus lead (Pin 10) was soldered to J2 pin 2, which is +5 volts.

The results are good.  I can run the local Data Net without fear of background noise, and I don't have to unplug my mic cable.