Subject: FT757 Computer control

From: [email-masked] (Kevin Feeney)
Date: 12 Feb 1992 15:21:31 -0800

On the 757 and computer control, I've found it easy to do and it requires
very little hardware. The simplest interface I have built consisted of an
optoisolator and nothing else contained in a nine pin D-shell connector on
the rear of my laptop. The optoisolator is wired with the collector and
emitter across the data input pins on the rear of the 757 (emitter at
ground, collector on the data input pin). The LED side of the optoisolator
is driven very simply by wiring the LED connections such that the diode is
turned ON when the data pin sends a ONE (data pin goes to the RS232 level
of -3 to -15 volts). No current limiting resistor is needed because the
port hardware can only source 10 ma anyhow. When a zero is sent, the
polarity goes positive, but an LED is still a diode, so it doesn't conduct
in that direction. It works and has been in use in my car on long trips
with a program I wrote to scan my 757 through interesting frequencies, or
do channelised tuning and at home to scan interesting shortwave
frequencies. (it was very useful during the gulf war to be able to scan
tables of frequecies for interesting listening)

The 757 expects to see data at 4800 baud, and you have to follow the
information in the manual on how to send the data (basically you push 5
bytes of information onto a stack). I uploaded a program in Turbo Pascal
to CI$ several months ago that I wrote to control my 757. It's in the
hamnet software area and called something like 757CAT.ZIP. I think I put
the pascal source and the .exe both on there.

The only drawback I could see was that in the 757GX, there is no provision
to send data back out from the radio to the computer. But that doesn't
make a lot of difference. I think the GXII does do bidirectional data, and
my 736 will do some but basically the Yaesu radios are mostly set up just
to accept external commands simply and easily.

As far as the hardware requirements, none of the radios mentioned seem to
be any more hardware ready for computer control than the 757. They all
seen to require some sort of RS232 to TTL level interface box, usually
priced in the $100 range. And you can build a variety of homebrewed
solutions for that using max232's, 1488/1489's or doing it dirt simple
with the optoisolator idea above.

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