[WriteLog] Parallel Interface

[George Johnson]

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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