RTS PTT support for old rigs with no CAT PTT

[vk3chi]

I noticed during my forum searches that getting old rigs to work with Log4OM seems to be a regular issue.

This particular issue is that both Hamlib and Omnirig are only capable of engaging PTT via a CAT command. This presents a problem for several older rigs whose primitive CAT command set only gives them tuning data and mode settings, but does not have a CAT command to engage PTT. On these old rigs, the PTT connection is accomplished by a connection from the PTT socket at the back of the radio, to the RTS or DTR pin on the computer's serial port.

Because Log4OM relies on Hamlib and Omnirig to engage PTT, it's obvious that this won't work on older rigs even though other CAT functions work fine.

So a feature request for a future release of Log4OM, is to include PTT Control via RTS and DTR. This shouldn't present a port resource conflict with Omnirig (I'm not sure about Hamlib) because Omnirig "passes though" RTS and DTR to any application that requires it.

In the meantime there is a hardware workaround for those who are into Arduinos and other microcontrollers.
- connect your Arduino's Rx serial line in parallel with your radio's CAT Rx line, so that it receives the same data
- connect another general I/O pin to the PTT socket of your radio using optocoupler or relay
- edit and add [pmTx] and [pmRx] character string commands to the INI file used by your radio in Omnirig
- program the Arduino so that when it receives the character string in [pmTx] or [pmRx], the Arduino will assert or de-assert PTT.

Andrew
VK3CHI