I go on step further and use a reed relay to key the radio. This way I have
absolute isolation and can key solid state or tube rigs and not worry.
I have been using the same serial keyer since CT days with no problems.
Jim
> Kevin,
> You could use the Comm port CW line and the 4N33 CW circuit to drive your
> level translator.
>
> But the LPT port is a TTL output (5 VDC and Gnd) and does not have
> sufficient "drive" current to drive the LED in the 4N33. The LPT port can
> "sink" enough current but that current must be supplied by another 5 VDC
> power supply with its own return line connected to the LPT computer Gnd
> line. I have tried to drive the LED from the LPT port here and it is both
> risky and unreliable. It is risky in that you may burn out the LPT
drivers.
> It is unreliable because when you limit the drive current you get may or
may
> not provide sufficient current to adequately switch the 4N33 output stage
> and key your circuit.
>
> I have thought of trying to steal the additional 5 VDC from the computer
> itself but have not tried it yet. I just use the 2N2222 circuit directly
> and have not had any ground loop problems in that circuit in several years
> of contesting. It will drive your level shifter nicely. I have used that
> circuit here also... (with a TS 530)
>
> George .. W1ZT
> ----- Original Message -----
> From: Kevin Stover
> To: Writelog@contesting.com
> Sent: Friday, July 06, 2001 5:03 PM
> Subject: [WriteLog] Parallel Interface
>
>
> Hello all.
> In response to my last message it was suggested that I use an
opto-isolator
> in the parallel interface to the rig to absolutely isolate the computer
from
> the rig.
> Can I swap out the 2n2222 in the parallel circuit for the 4n33 of the
serial
> in the documentation.
> Either way this circuit is going to have to drive the grid block keying
> circuit of my last post.
>
> Writelog documentation: http://www.willinet.net/~kstover/cwint.jpg
>
> Grid block keying circuit: http://home.att.net/~jacksonharbor/gridbsch.pdf
>
> Thanks for the input.
>
> Kevin, NØRKX
>
>
>
> --
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>
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