The USB Mic Ptt adapter DIY project allows a hand mic, or hand/foot PTT switch to toggle the Tx/Rx of the radio when using RemoteTx on a laptop and some tablets. The adapter initiates a keyboard Shift-F19 signal via USB when the PTT button on the Mic is pushed. This causes RemoteTx to put the radio in Tx mode. When the PTT button is released a Shift-F20 signal is sent and the radio returns to Rx mode.
Pictured is the Heil HMM-IC: