[CQ-Contest] Optocouplers

Dave Hachadorian K6LL at ARRL.net
Sat Jul 4 13:37:04 PDT 2009

Hi Mark,


Let me see if I can summarize your findings regarding use of 
optocouplers on LPT ports:

1. Single stage optocouplers draw too much current from the 
LPT port.
2. Darlington optocouplers don't bring the key line close 
enough to zero volts to key reliably.
3. To get the CW key line to work with an optocoupler, you 
used a 4n32 darlington optocoupler to drive a linear 
comparator IC with a comparison threshold of 3V and VCC of 
5V to convert to reliable TTL levels, then a TTL driver IC 
to key the rig.

I hope I got that right. Pretty wild stuff.

I haven't had any problems using just an npn transistor, 
even with multiple 1500 watt amps blasting away.


Dave Hachadorian, K6LL
Big Bear Lake, CA

----- Original Message ----- 
From: "Mark - K5AM" <k5am at zianet.com>
To: "Dave Hachadorian" <K6LL at ARRL.net>; "cq-contest 
reflector" <cq-contest at contesting.com>
Sent: Saturday, July 04, 2009 12:05 PM
Subject: Optocouplers

> At 2009-07-04 17:03, Dave Hachadorian, K6LL,  wrote:
>>I had trouble using optocouplers. They wouldn't key the 
>>rig.   . . .
> Dave,
> A reliable system using optocouplers appeared in:
> QST, Sept 2004, 28-33.
> The expanded version, with schematics and details, is 
> available at:
> http://www.arrl.org/files/qst-binaries/hapirat.zip
> Best regards,
> Mark, K5AM
> www.zianet.com/k5am

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