Posted by
Ward Willats-3 on
May 24, 2005; 5:46am
URL: http://elecraft.85.s1.nabble.com/K2-Autodetect-keying-circuit-tp378683.html
I know one of you smart folks will easily have some advice off the
top of your head:
I built an opti-copupled keying circuit in a D-Shell, driven by pin
17 of my parallel port and use n3fjp's logging software to drive it.
The coupler is a 4N35 and the current limiting resistor is 1.2K. The
basic schematic is from N3FJP's web site:
http://n3fjp.com/rigcw.htm
-- except I added two 1N5817 shottky diodes to trip the auto detect.
Well, the scope shows everything is wiggling, but the keylines are
only being pulled down about 3 volts (from around 7). I assume I need
to pull the line a lot closer to zero before the K2 will key!
Before I go stabbing around blindly, I thought I'd ask what I need to
do to get more drive. My thought is I can do some math and drop the
current limiting resistance on the LED so it shines more brightly in
there, but maybe there are other factors (such as the maximum current
the parallel port can source) that I should know about before I start
down this road.
Thanks,
-- Ward / KG6HAF
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