[Elecraft] K2 dual keying problem

[Alexandra Carter]

Is is possible to add a de-bounce circuit to the hand key? 73 de Alex 
NS6Y

On Feb 5, 2006, at 5:41 AM, Don Wilhelm wrote:

> David,
>
> I would rather speculate that it is a uP timing situation coupled with
> contact bounce at the key and the forward voltage drop of the diodes.  
> If
> one of the diodes is a bit slower than the other, the voltage seen at 
> the uP
> pins may actually look like one pin has gone to a low state before the 
> other
> (that is the condition to generate the iambic alternating dots and 
> dashes).
> This problem can be caused by contact bounce at the hand key - 
> cleaning the
> hand key contacts will help, but one can never cure contact bounce at a
> mechanical closure point.
>
> The net of the story is that the uP must believe that both the dot and 
> dash
> contact closures occurred together, and the only way that can be known 
> is
> for it to sense a low voltage on both its input pins.  If the polling 
> of
> those pins happens to occur during a contact bounce period and one of 
> the
> diodes is a bit slower than the other it will appear to the 
> microprocessor
> that only one of the contacts was closed.
>
> I am surprised that two diodes in series appears to work better - in 
> fact it
> will make the low state at the uP pins at an even higher voltage than 
> one
> diode.  I would suggest that you try using Shottky diodes (like 1N5711)
> instead to lower the voltage at the uP pins when the hand key is 
> closed.
>
> So clean your key contacts and go back to one diode for each side and 
> if
> still a problem switch to Schottky diodes.
>
> 73,
> Don W3FPR
>
>> -----Original Message-----
>
>>
>> Mindful that I am neglecting my hand keying, my sending being spoilt 
>> by
>> the ease of using an iambic paddle, I have connected a straight key
>> across the paddle keying line using a pair of 1N4148 diodes as shown 
>> in
>> the K2 Manual.   This works reasonably well, but occasionally when
>> pressing the straight key I get a string of alternate dots and dashes.
>>
>> I presume that the problem is caused by the reverse resistance of the
>> diodes being too low.  I tried putting two 1N4148 diodes in series in
>> both lines. This is better but has not cured the problem completely. 
>> Has
>> anyone else had this problem? Or does anyone have a suggestion as to 
>> how
>> both a paddle and straight key may both be connected to the K2 with
>> reliable results.
>>
>> 73 de David G4DMP
>>
>>
>
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