[Elecraft] [K1] CW Paddle Contact Bounce

[Vic Rosenthal 4X6GP/K2VCO]

You don't mention the material the contacts are made of. A few years 
ago, one major manufacturer of high-quality paddles was using a 
particular alloy for contacts which behaved like a semiconductor 
junction. In other words, it had a fixed voltage drop despite the amount 
of current that was flowing through it. This upset circuits like that of 
the K1, which distinguishes dits and dahs by detecting a voltage drop 
across one of a pair of resistors grounded by the paddle.

I thought at first that it was a bounce problem. I tried various 
solutions, but the only one that ultimately worked was to get the 
manufacturer to supply silver contacts for the paddle in question (gold 
plating and maybe some other materials are also OK).

On 24 Feb 2015 23:40, David Brown wrote:
> I have owned a K1 for almost 15 years and have always used it with either a
> straight key or an external keyer. I have never had a keying problem with
> the K1 other than operator errors. Last year I purchased a single lever
> paddle to use with the K1's internal keyer. Much to my surprise,
> significant keying errors occurred when this new paddle was used with the
> k1's internal keyer. With the K1's internal keyer set for 20 WPM, I could
> not complete sending the entire alphabet without at least one keying error.
> I discovered that sending the Morse letter “A” multiple times, the K1 would
> occasionally transmit the letter “N”. Steve, N8WL, used his much newer K1
> with my new paddle for this experiment. Sure enough, Steve had about the
> same error rate as I had with my K1. I should mention that my K1 has been
> updated with the latest updates, including the MCU firmware which matched
> that in Steve's K1. So just what is the problem here?
>
> Paddle contact bounce was the prime suspect in these keying errors at this
> point. I decided to investigate what contact bounce may exist and how the
> K1 deals with it before doing any paddle adjustment or contact cleaning. I
> instrumented my K1 with two oscilloscope probes connected to the K1's MCU
> that, in addition to performing K1 control functions, controls transmitter
> keying and the Iambic mode keyer implementation. One probe was connected to
> the MCU keying input and the other to the keying line output that keys the
> transmitter. A fairly lengthy investigation can be summarized with the
> following observations. First, paddle contact bounce was very prevalent.
> For example, the dot contact bounce typically ranged between 3 and 6
> milliseconds, but had some occurrences as high as 8 milliseconds. It
> appears that in the presence of contact bounce, a false detection of a
> contact closure can occur when the MCU keying input voltage must transition
> through a region that represents a valid but unintended contact closure. In
> the Morse “A” experiment, the MCU keying voltage will initially switch from
> 6.1 volts down to 1.9 volts with the dot contact closure. In doing this,
> the voltage will drop through the vicinity of 3.8 volts which represents a
> dash contact closure. The MCU A/D conversion and firmware that monitors
> this voltage sometimes mistakenly recognizes this transition as a valid
> dash contact closure that is followed by a dot contact closure. When this
> happens, the dash contact closure used in sending “A” appears to be ignored
> while “N” is being transmitted by the K1.
>
> The K1's paddle contacts are connected to the MCU keying input via a
> resistor network that adjusts the MCU input voltage to the values used in
> identifying specific paddle contact closures. Capacitor C6 (.01 uF) at the
> MCU keying input provides some RC filtering to this keying voltage. Varying
> the size of C6 had a very strong influence on the percentage of keying
> errors. Larger values of capacitance increased the error rate while smaller
> values decreased it. This makes sense in that with a larger C6, the voltage
> transition through that "dash contact closure" region is increased in the
> "A" experiment, thus increasing the probability of a false contact closure
> detection. It is a difficult problem to design a real time A/D conversion
> and voltage detection system that meets acceptable A/D charge holding times
> in the presence of significant contact bounce. I wound up changing C6 from
> the stock .01uF to 100 pF which in turn significantly reduced false paddle
> contact closures. In addition to this, paddle adjustments were made to
> further eliminate this problem. The contact bounce error rate is not zero,
> but it has been reduced to a low background level that is well below my own
> paddle use errors. All of the data recorded in this investigation is
> presented in a short article in the January 2015 issue of the QRP Quarterly
> (http://www.qrparci.org/). I would be interested in hearing from others
> that have dealt with contact bounce issues involving the K1.
>
> 73, Dave K8AX


-- 
73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/