I use a single COM port for CW keying, the TNC and an SSTV converter.
The circuitry is built into a commercial RS-232 A/B switch box, this
simplifies the hardware side of the project.
Since only a few of the RS-232/DB-25 pins are required to operate a
TNC/SSTV/CW keyer. Most of the wires can be removed from the switch box.
This leaves plenty of room for circuit boards and plugs. The now unused
poles on the switch can be used to switch audio and PTT lines.
One position is straight through to the TNC. A DPDT toggle switch enables
the CW keyer. (CT supports this configuration)
Switch position two goes to the internal SSTV converter.
This works out well...I can contest on CW and use my TNC for spotting....or
play with SSTV. one switch does it all.
(I can't run the TNC and SSTV software at the same time so this works out.)
For flexibility, I use a separate box to switch the audio, mike, PTT lines
between HF,VHF, rigs.
The CW keyer uses a Radio Shack Reed Relay to provide isolation between the
rig and the computer. (I also use tube gear and I wanted one interface.)
Why all this bother???
COM 1 goes to the switchbox.
COM 2 runs the OMNI-VI
COM 3 is my modem
If I add a COM 4 it will be for rotator control...
73, Jim WB2TPS
>Hi Paul:
>I f your local store has the usual replacement series from ECG or
>NTE - either the 3044 or 3045 works great. They have a
>Darlington Pair output, so that you get a good clean on/off
>pulse.
>I built all of mine into the serial connector at the computer. As in
>most cases, there are pins that are not used in the connector, so you
>can cut them off with a pair of dykes. Then, epoxy glue the opto-isolator
>onto the area that doesn't have pins. A 1/4 watt, 1000 ohm resistor will
>go from the Anode (pin 1) to what ever keying line is used.(Usually
>the DTR line of a serial port, or the SLCT line of a parallel port.)
>The cathode will then go to the computer ground for a serial port or
>to the STROBE line of a parallel port.
>Run the key line from you transceiver through the normal cable hole and
>strain relief of the DB connector and tie to the output, Pins 4 & 5.
>When you put the housing on the connector, it looks just like a normal
>serial cable, very sanitary.
>The Opto-isolator will switch considerably faster than you can send cw,
>so there is no concern of character dropping.
>Here and at the local contest stations, these have been in use for
>about 7 or 8 years with no ill effects.
>Good Luck.
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