K2 Keying current?

[Chris Kantarjiev K6DBG]

I'd like to build a parallel port keying cable for my K2. Lots of schematics
on the web, all calling for a 2N2222. I find that I don't have any of
those in my junk box right now (horrors!) but have lots of 2N4124;
the big difference is that the 4124 is limited to 200mA collector current.

It seems like this should be enough, since the keyer contact goes
straight to the MCU ... right?

73 de chris K6DBG
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[Jim Brown-10]

On Thu, 2 Aug 2007 09:35:19 -0700 (PDT), Chris Kantarjiev wrote:

>2N4124;
>the big difference is that the 4124 is limited to 200mA collector
current.

This is a rather non-critical part. Anything that's close works fine.
I've built at least a half dozen of them for four different radios with
a 2N4123.

73,

Jim K9YC



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[Tom Hammond-2]

Chris:

Just about any(!) general purpose NPN will work.

If you're interested in a PC board design which includes PTT, go to
the "general info' page at www.n0ss.net and take a look at the design there.

73,

Tom Hammond   N0SS

At 11:35 AM 8/2/2007, Chris Kantarjiev wrote:

>I'd like to build a parallel port keying cable for my K2. Lots of schematics
>on the web, all calling for a 2N2222. I find that I don't have any of
>those in my junk box right now (horrors!) but have lots of 2N4124;
>the big difference is that the 4124 is limited to 200mA collector current.
>
>It seems like this should be enough, since the keyer contact goes
>straight to the MCU ... right?
>
>73 de chris K6DBG
>_______________________________________________
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[Don Wilhelm-3]

Chris,

The maximum keying current required by the K2 is limited by the 5 volt
sourced by the MCU input and its pullup resistors.  There is a 220 ohm
resistor in series with the signal line - so the maximum current will be
23 ma.  Most any garden variety NPN transistor will do the job for you.

73,
Don W3FPR

Chris Kantarjiev wrote:

> I'd like to build a parallel port keying cable for my K2. Lots of schematics
> on the web, all calling for a 2N2222. I find that I don't have any of
> those in my junk box right now (horrors!) but have lots of 2N4124;
> the big difference is that the 4124 is limited to 200mA collector current.
>
> It seems like this should be enough, since the keyer contact goes
> straight to the MCU ... right?
>
> 73 de chris K6DBG
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
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>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>

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[Chris Kantarjiev K6DBG]

Thanks for all the responses. I got this working pretty quickly yesterday.
It took two iterations ... first time, I made the cable a bit too
short in my effort to keep my desk neat - and had some of the connections
off-by-one on the DB25 :-) The computer would key the radio but never
unkey.

I figured that out and added a foot of cable and N1MM logger is happy...

73 de chris K6DBG

P.S. http://pages.cthome.net/n1mm/html/English/Interfacing.htm has schematics,
among other places. And Tom N0SS's board looks very nice, but I
wanted it "today". I also wanted to put the isolation diodes in a
(planned) box that will take computer, paddle and straight key...
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