[Elecraft] K2 Autodetect keying circuit

[Ward Willats]

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