[Elecraft] K2: Erratic action of the Hand Key "Autodetect" function

[Jim Sheldon]

Picked up a couple of 5711's from our local "surplus" electronics dealer.
They appear to do the trick - hasn't glitched once since I switched out the
4148 (914) diodes.

Jim

> -----Original Message-----
> From: Tom Hammond [mailto:n0ss at earthlink.net] 
> Sent: Monday, May 09, 2005 4:15 PM
> To: svholm2 at broadpark.no; 'Jim Sheldon'; elecraft at mailman.qth.net
> Subject: RE: [Elecraft] K2: Erratic action of the Hand Key 
> "Autodetect" function
> 
> 
> If Sverre's solution to the problem (Schottky diodes) is the 
> answer, then 
> the 1N5711 should work nicely... and they are pretty easy to 
> find... even 
> if you order them from Elecraft.
> 
> 73,
> 
> Tom   N0SS
> 
> At 02:14 PM 5/9/05, Sverre Holm wrote:
> >-----Original Message-----
> >My K2 (and I've talked with several other K2 owners with the same 
> >problem), Serial #4338, will not always detect a hand key 
> properly -- 
> >Autodetect is turned on in the menu - and I am using 2 1N914 diodes 
> >between the hand key contacts and the dot and dash inputs to 
> the K2.  
> >The keypaddles function properly at all times, but when 
> using the hand 
> >key, at random times, a key down on the hand key produces the same 
> >results as a paddle press - namely automatic dots or dashes.
> >----
> >
> >I have resolved a similar problem some time ago that 
> hopefully may shed 
> >some light on your problem also. The symptom appeared similar, 
> >seemingly random keying.
> >
> >The series diodes in the autodetect circuit will make the K2 
> input no 
> >longer 0, but say 0.7 Volts (for Si diodes) when keyed. When 
> I tried to 
> >key the K2 using autodetect and the diodes from my PC via an 
> >optocoupler I got into trouble. The saturation voltage of the 
> >optocoupler was not small enough and when added to the 0.7 
> Volts, the 
> >total was not low enough for the K2 to reliably sense a key-down.
> >
> >The optocoupler (4N31) had a voltage of 0.65 to 1.8 V in 
> saturation. I 
> >lowered it by increasing the drive current in the LED, but still had 
> >almost 1.4 V (opto 0.65 + Si diode 0.7). The remedy was to 
> replace the 
> >autodetect diodes with Shottky diodes. I have several hundreds of 
> >PRLL5818 in my shack so I used one of them, but the type is not 
> >critical at all. The data says Vf < 0.33 V at I = 100 mA, so the 
> >forward voltage with the low current here is even smaller than that.
> >
> >73
> >
> >Sverre
> >LA3ZA
> >http://www.qsl.net/la3za/
> >
> >
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