Re: Momentary Switch Circuit

Terry Pinnell wrote: 
ehsjr <ehsjr@xxxxxxxxxxxxxxxx> wrote:


Terry Pinnell wrote:



I use a PC-based 'scope. It's an ADC-200/50 from Pico Technology
http://www.picotech.com/
Wouldn't like to have to manage with only my Hameg analog scope. On
the other hand, it is good to get away from a PC for a while!

I take a screen capture (various ways; I use Snagit), and paste it
into PaintShop Pro 7. Occasionally I might edit it there, adding some
explanatory text etc.



I'm using different values to get the whole
picture on the display - I can't see 5 seconds.



Was there meant to be a link here to your display?


No.  The only way I can capture scope waveforms by taking a picture
of them. :-(


That was major motive for buying the PC-based scope. A digicam is OK
at a pinch, but not in the same league.


Some observations:
I missed the time scale on your 5 second waveforms and the voltage
scale on the right.  My scope doesn't do that! :-)  Took me a
while to catch on to how to read them.



Yes, I'd begun to suspect that you weren't reading the red scale <g>.



Your comment about Vout = Vcc-Vz is correct. Henry also
pointed that out.  I saw your first waveform showing a 14 volt
Vcc with a 12 volt zener yielding an "8" volt output, which
makes no sense either way - but now that I understand how to
read the waveform, that "8" volts is actually 2 volts, which
does make sense.  So toss the zener from the circuit.



I'd go further. To mis-quote an old Python sketch: That circuit is
deceased, no longer with us, kicked the bucket... <g>.


Nope.  The circuit works sans zener for devices that accept momentary
swicthes as input and have a built in debounce.



OK, agreed.


During the switch noisy time, I get some beautiful
transitions on the bounces like you have in the first
transition in Ed-11, but I view it at .1 ms per div.
How wide is your first transition? Mine varies from
.1 to .2 mS.


Not exactly sure what you mean. As shown by the X-axis timescale, in
Ed-11 I was using 20 ms per division, and 100 ms in Ed-10.

Right. What I'm calling the first transition starts at 0 mS,
goes up to 2 V then down to 1V, where the greatest amoubt of noise starts. I'm wondering what is going on during that period.
I get about the same waveform, and the period for the
first transition varies from ~ .1 mS to ~.2 mS - I'm using
a Tek 485, & get the same thing on a Tek 475. 


OK, I see what you mean. But, if they do indeed follow that sort of
pattern no idea why. Switch bounce is something of a black art <g>.
Several toggles I tried were exceptionally low on noise. That
particular one exceptionally high. Presumably, if pole and both
contacts are connected to +Vcc and 0V respectively, swings must always
be across full supply, with no intermediate values possible. Maybe if
I'd set my timescale down to say 5 us I'd see even shorter pulses?


The former

was with a 5 uF cap, and the latter with 1 uF. In both cases I was
starting with toggle open, and then quickly closing and re-opening it
(about 300 ms), and then not repeating for several seconds.

BTW, that particular switch is one I reserve when I want to be sure of
seeing the effects of *lots* of noise.

But it's all rather academic now! 

Yup. But it got me to wonder if anyone else uses toggle
switches in place of momentary.  I'd never considered or heard
of doing that until the OP made his post. I did make a
relay "one-shot" once - OP needed a relay to energize for
one pulse at shut down. The supply energized a relay when power
was on. The open point charged a cap. When power was turned
off, the relay dropped out and transfered the charged cap to
a second relay:

+Vcc ---+---[RY1]---+-----+--- Gnd
       |           |     |
       o NO       [C1]   |
        \          |     |
 RY1-1   o---------+     |
                         |
       o NC              |
       |                 |
       +-----[RY2]-------+

I never did learn why he wanted that circuit.



Did you also see my later follow-up yesterday?
news:5d8li116vik3lnfkc0pbaqs2b8fpu1sgn8@xxxxxxx


Yes. If both VCS1 and VCS2 are simultaneously energized,
D1 input "sees" the input to VCS1 normally open point -
not a good thing. The 14v spike might be that condition?

Ed
.

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