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Author Topic: Need help with Keying rig using serial port  (Read 580 times)
KU4UV
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Posts: 376




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« on: April 17, 2009, 07:33:58 PM »

Hello guys,

I have an old Toshiba Satellite 110CS laptop computer that I am using for my digital mode operating.  I am running Windows 98se and WinPSKse 2.23 software.  I am using a Unified Microsystems SCI-6 soundcard interface, and the transceiver is an Icom 718.  I have been using the transceiver's VOX control to key the radio, but I would like to be able to key the transceiver using the computer's serial port.  I tried using the DB-9 connector and keying the rig using RTS/DTS, but I am unable to get the software to key the transceiver.  I'm not sure if the settings in the computer are incorrect, or what the problem might be.  I double-checked that the correct pins are connected, and when I short the PTT wires, the rig is keying fine.  I also checked that the COM port was selected in the software, but perhaps I missed something.  Can anyone that is running WinPSKse or Windows 98se help me out with any thoughts or suggestions?  Thanks for the help!

73,
Michael KU4UV
ku4uv@arrl.net
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K0BT
Member

Posts: 196




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« Reply #1 on: April 19, 2009, 10:44:26 PM »

The serial port can be used to drive a transistor switch for keying, but it will probably not switch your transmitter by itself. If your TX only needs to switch 12 volts at a few milliamps to ground, you can try making a single transistor switch by conecting a NPN (2N3904/2N2222,NTE123, etc.) transistor as follows:

- 1K resistor from serial port pin to Base
- Emitter to ground (maybe through a current limiting resistor)
- Collector to TX line of radio
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WA9UAA
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Posts: 321




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« Reply #2 on: April 23, 2009, 01:37:35 PM »

Michael,
The pins on the computer port are probably being driven "high" as in the voltage on the pins is going up. What you need is indeed a transistor switch ie. open collector, to make a "short" across the key line of the rig when the transistor is being turned on. There are plenty of keying circuits in literature for the various digital modes.
73,
Rob WA9UAA
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W0GLB
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Posts: 45




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« Reply #3 on: May 22, 2009, 08:10:42 AM »

If you are looking for a ready-made solution, here is one I have been using effectively for several years now:  http://www.hosenose.com/interfaces.asp#keyer

73,
W0GLB Gordon
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KT4WO
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Posts: 154


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« Reply #4 on: May 30, 2009, 06:14:37 PM »

I have found that many Laptops do not put out "True"
RS-232 voltages(-12/+12VDC) many are just 5VDC...If you are using a 2N3904/2N2222 as the keying "relay"..It will not work sometimes.

Not sure what you can do, but that may be the problem.

KT4WO
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KT4WO
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Posts: 154


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« Reply #5 on: May 30, 2009, 06:15:10 PM »

I have found that many Laptops do not put out "True"
RS-232 voltages(-12/+12VDC) many are just 5VDC...If you are using a 2N3904/2N2222 as the keying "relay"..It will not work sometimes.

Not sure what you can do, but that may be the problem.

KT4WO
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K3AN
Member

Posts: 787




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« Reply #6 on: June 03, 2009, 11:53:18 AM »

+5 volts is more than enough to drive the base of a NPN small signal transistor. Connect a resistor between the serial port pin and the transistor base. The resistor value should be chosen to limit the base current to a milliamp or so (10K should do). Connect the transistor's emitter lead to ground and the collector lead to the radio's key lead. You should also connect a diode from base to emitter, with the anode lead connected to the emitter. This will limit the reverse base voltage to less than 1 volt for when the serial pin voltage goes negative.

Using the DTR or RTS lead to send Morse requires use of the computer's clock. You might get away with that if you're running Win98SE, but with Win XP and later Windows operating systems, the computer is doing so many things in the background that the Morse element timing will be badly mangled. With 98SE it has been my experience that only 10% or so of the characters are mis-timed. With XP and later the Morse sounds like the classic QLF (sending with the left foot) operator.
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W5DQ
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« Reply #7 on: June 05, 2009, 03:51:18 PM »

"... but with Win XP and later Windows operating systems, the computer is doing so many things in the background that the Morse element timing will be badly mangled."

I disagree. I use a homebrew interface that combines 2 inputs: 1) a K1EL outboard keyer with Virbroplex Vibrokeyer and 2) the serial port RTS signal to key up my TS-940S. I use Windows XP (latest Srv Pks) and when operating CW, usually have DX Lab Suite, MixW, Firefox and other apps open and operating with no problems whatsoever in the timing of CW sending via the RTS signal. My PC is a 2.6 Ghz Dual Core AMD with 4 GB of RAM. No pain, no strain in my operating CW, up to 40 to 50 wpm (I tested it that fast, NO WAY I could operate normally that fast Smiley.

Blanket statements like the quote above are confusing to many operators and need to have a caveat added. I will agree that if you have a slow PC and limited memory, you could easily get to a point where the hardware has too much latency to effectively run a digital CW keying interface.
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Gene W5DQ
Ridgecrest, CA - DM15dp
www.radioroom.org
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