With work on the PC side of my digital interface complete last night, I was able to try out whether my wiring of the RTS pin on the serial cable was a success. The idea being that the RTS is signalled by the software when you wish to transmit. In my interface this then drives a relay which switches the PTT on the radio side.
Inline with the RTS I've added a LED so that I can see what is happening for ease of any required debugging. I'm glad I did!
Turns out, my laptop has RTS signalled/on by default. As soon as I hooked up the serial line to my computer, the LED lit up. This would mean, if my radio was on and connected to the computer via 'the interface' then it would immediately start transmitting from computer start-up – not so good. However, it turns out that this is not unusual, but none the less most of the interfaces and thereby the software utilise RTS to control PTT.
So what does one do? Well, on Windows people use the 'mode' command line tool to have windows change the RTS at start-up (but none the less, there is still a period there where it will be active). On Linux though I'm not entirely sure what command I can use. But ideally, I think what is really needed is a simple switch in the RTS line to switch off the unit when not in use. Once I get things working I might look at that as one of the first modifications. For now though I'll just have to make sure I don't leave things connected.
Tonight though I'm looking forward to wiring up the radio side of things! I've got most of it done but back to front at the moment (shouldn't have rushed it in my lunch break), so hopefully it wont take to long to fix up. Not long now until I can finally do digital – only been waiting about 3 years. 😉
(Oh, and other than discovering RTS is commonly always on – thanks Google – when I launched fldigi and configured it, the T/R functionality worked perfectly and thereby I confirmed I did have everything wired correctly – again, thanks to the little LED that could. Shame I didn't have the same success on the radio side at lunch today…..)