The LED Herring

My PC/Radio interface is finally 100% working, but that was not without some hurdles. You would have seen my previous posts about inverting the logic for RTS etc. Well, that was all due to a simple mistake which was most likely due to me rushing as I was excited to get it built and try digital modes!! 🙂

In a previous post I noted how happy I was that I included an LED in my interface to show me when it was receiving a transmit signal. This was added to allow me to easily see what the software was doing in case I had it misconfigured. However, what I didn't do was use it to check whether the interface was built properly. That is, I assumed that the LED (and thereby the connection to RTS on the computer) circuit was flawless.

Well, it turns out I was wrong – and something I should've checked.

But due to my reliance on this, I was under the impression that my computer was sending a -ve voltage when RTS was being asserted, and then a +ve voltage when it was essentially idle. Hence, I modified the WSPR code and configured other software in wonderful ways. But in the end, after measuring voltages (rather than just looking at my pretty lil' LED) I came to realise that my serial port was working as it should (+ve voltage on RTS, -ve on idle). The problem was, I had mixed up my GND and RTS wires!!

Seeing that the RTS voltage switches between +ve and -ve (not just +ve and 0 – another poor assumption I made) it meant my little LED would light up even if things were back to front – not only if things were perfectly wired. Therefore, even though everything looked as though it was working, it was working back to front.

So, hopefully I've learnt a few lessons there, and will measure things a bit more closely and not get too lost chasing Red/LED Herrings. But now with all fixed, I'm wired for digital!!

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