Bob,
You also need to check pin 1, which is connected to the emitter of the
keying transistor. The LPT port completes the keying path to ground for
the keying transistor. You should measure with a voltmeter from pin 1 to
ground while NA is keying to make sure its working - this should be not
more than a few tenths of a volt DC.
If pin 1 is suspect, try moving the keying transistor emitter from pin 1 to
one of the ground pins (anything from pin 18 thru pin 25. If it works then
the LPT pin 1 circuitry may be hosed.
OTOH, if the voltage drop across the keying transistor and pin 1 to ground
may simply be too high for your radio. You can confirm this by taking an
assortment of resistors and finding the highest resistance which will key
the radio. Measure the voltage drop across the keying line with this
resistance and see if its lower than the voltage across the keying
interface. If so, you may need a different interface.
If that's the case, I can help you with a different circuit. One
possibility is to get a fast reed relay (available from Radio Shack,
Digikey and other places) and let the interface key the relay, and the
relay key theradio.
73,
Dave/K8CC
At 12:52 PM 8/12/02 -0400, Robert L. Kellogg wrote:
>Guys,
>
>I need some serious help here.
>
>I'm trying to get NA to key my rig. It's beginning to look like
>there is a problem with the Computer/Interface. That is, the standard
>parallel port interface won't work.
>
>NA is doing everything it should, I think. I checked the voltage on
>pins 17 and 18 of the db-25 parallel port and it changes from about .06V
>to 2.5V or more when the computer sends code. The voltage varies with
>the code sent. (in other words, I can see the dots and dashes.)
>
>Scope shows the same voltage change, however, I also saw some RF along
>with the DC voltage. A .001 capacitor between pins 17 and 18 seemed to
>eliminate the RF, but The rig is still not keyed.
>
>I've checked the cable. Actually, I made a little db-25 with the
>interface circuit on it in the open so I could check voltages, etc.
>
>I need some electronics help here. Anybody know what the parallel port
>is supposed to do, and how to convert it's action to a switch that will
>key the rig?
>
>I connected my hand key to the rig and verified that it keyed OK. Then,
>I connected the above circuit in parallel with the hand key. This
>circuit operated as above, but would not key the rig.
>
>Can someone help with this problem? I suspect that my computer is
>working in a different manner than earlier models, and it may require
>some changes in interface design. Of course, I could be nuts, and need
>to put my tongue on the other side of my mouth when I key... Whatever
>the solution, it escapes me.
>
>Help!
>
>--
>73,
>Bob Kellogg, AE4IC
>Prolably, not nececelery. -Benny Hill
>
>
>
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