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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