[Elecraft] K2 dual keying problem

[Don Wilhelm]

Alex,

It certainly is, but most circuits using a single pole single throw switch
(normal key contacts) suffer from the same difficulties as the K2 key input
circuits - one must make some assumption about the duration of the bounce
and decide if it is a valid key closure or not.  To do it in a foolproof
manner requires a SPDT switch, and the closure of the NO contact sets a
latch, the closure of the NC closed contact resets it - simple set/reset
latch, no clocking required.

So if one were willing to swap their favorite hand-key for one with a SPDT
set of contacts, it would work flawlessly - perhaps someone else will come
up with a better method, but that is the circuit that I have used for
de-bouncing when complete assurance of a contact closure is required.  Noise
on the set contacts may get through, but will not set the latch because the
reset contacts are still closed.  A couple of 2 input NAND logic gates and a
couple of inverters will do the job nicely.

In the meantime, I will use an external keyer and leave the K2 set to INP
Hand to accomplish the same task - the K1EL K12 keyer is small, can run a
long time from a coin battery and does the job for me.  I am not knocking
the K2 keyer, but I am getting used to my K1EL keyer and I can use it with
any rig with no time to become accustomed to a particular internal keyer.

73,
Don W3FPR

> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net]On Behalf Of Alexandra Carter
> Sent: Sunday, February 05, 2006 8:04 PM
> To: w3fpr at arrl.net
> Cc: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K2 dual keying problem
>
>
> 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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