I decided to move all my radio stuff from my desktop to my laptop for now. My desktop has never been a reliable computer - there's something wrong with it that causes it to stall (and whatever it is, it's hardware and not OS, as it has done the same with XP or Mint).  It also goes SLOOOOOOOOOOOW.  In fact, it goes so slow, I tend to boot it at least 10 minutes before I need it, and it was degrading to the point where it wasn't even ready then.

So, one thing I ~need~ want to be able to do is digital modes like RTTY (I know many hate it, but I do enjoy RTTY contests).  The problem I ran into is not a new one: there's no serial port on my laptop, meaning my old way of triggering my radio's PTT is now a useless group of components.

I happen to have a Sparkfun FTDI Breakout board sitting nearby.  It has a damaged trace to the 5V output caused by the fact that my soldering iron is an old Radio Shack 45W pencil (which puts out far too much heat for many boards).  I had set it aside with the intent to use a wire jumper to fix the problem, but after getting it back off the electronic triage shelf I realized that everything worked except the 5V output.  The module looks like this (picture credit from Sparkfun):

10008-01

I first wired it in with my transistor switch to look something like this:

oldptt

It didn't work.

I started to investigate.  I noticed that DTR, RX1, TXO, and CTS were all 5V, but DTR would drop to 0V when the DTR was activated via software.

So I did a little research. FTDI makes their boards customizable, so I looked into the software from FTDI's website and found a configuration utility called FT_PROG.  From this utility, I was able to read the chip and then re-write the chip to invert the DTR signal.  Note the screenshot below:

InvertedDTR_Software

This allows me to use the FTDI board with an optoisolator and trigger the PTT.  The schematic is below:

newopto

So now I just have to fix the USB soundcard issue...

-73-


Category: Equipment

About the Author

Andrew is the owner of this blog and enjoys computer programming, building things, and photography. He’s a pretty busy guy, which explains why updates to this blog are so infrequent.


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