debouncing a switch (in hardware)

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I've been messing around with my own sort of development board for an
Altera MAX 3064 because I have some downtime at work (I'm a coop) and
wanted to teach myself some PLD stuff.  I wanted ot put a manual clock
button on it so I could just mess around with some simple designs to
get a feel for how to use HDL's and Quartus.  I have some DIPs for
inputs and LEDs for outputs, everything run on 3.3V.   But the I can't
manage to get the clock to pulse just once when I press the button.
Can anyone recomend a debouncing circuit to use for something l like
this?


Re: debouncing a switch (in hardware)

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Best way of all is to use a single pole change over switch and a set-reset
circuit (cross coupled two input nands).
Guaranteed to give bounce free output without any tricky time
constants/capacitor slugging/timers etc!

http://www.wheelnut.plus.com/sr.gif

(excuse poor drawing!)

HTH

Slurp



Re: debouncing a switch (in hardware)

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Google "switch debounce."


    ~Dave~

Re: debouncing a switch (in hardware)
Hi -

On 6 Jul 2006 11:53:39 -0700, "Brian McFarland"

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Jack Ganssle has written extensively about this.  Here's a paper that
summarizes his findings and design suggestions:

http://www.ganssle.com/debouncing.pdf

Bob Perlman
Cambrian Design Works
http://www.cambriandesign.com

Re: debouncing a switch (in hardware)
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  On this general subject, does anyone know of a LOW PROFILE microswitch
action ( SPCO / SPDT ) switch ?
  There are std microswitches, which tend to have a high profile, and
couple of old ITT style snap switches, also ~10mm high, but nothing I
have found is close to a tact button, with SPCO ?

-jg


Re: debouncing a switch (in hardware)
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Here is an article in ECN about some Ultraminiature Mircroswitches from Tyco
http://www.ecnmag.com/article/CA6339402.html?nid27%30&rid16%35558756

--
Greg



Re: debouncing a switch (in hardware)
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Thanks, yes, seen that.
The microswitch market is industrial-legacy: what they call
"Ultraminiature Mircroswitches" are around 12.7mm long - which is
what the semiconductor sector would consider "quite large" :)
-jg




Re: debouncing a switch (in hardware)
Jim,

Have you tried ALPS?  http://www3.alps.co.jp/alpscom /

I haven't looked to see if they carry what you want; but their name
immediately came to mind upon hearing your request.

Rob


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Re: debouncing a switch (in hardware)

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I just finished implementing a small protoboard with 12 unbonced
switches, I used a safe SRLatch type approach :-)

And it works like heaven ;-)




Re: debouncing a switch (in hardware)

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SRLatch works with SPDT, if you need to debounce SPST, which is more
common, you need to have something with a timing circuit in it like the
Maxim MAX6817 dual switch debouncer:

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1896

As I recall switch debouncer IC's have been around since early days
of 4000 series CMOS.

Have Fun,
Gabor


Re: debouncing a switch (in hardware)
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Yes of course for SPST amd unbounced pulse you can go with something
like MAX6818  (they have free samples):-)

I choose SPDT and SRLatch because I wanted unbounced transitions and
stables states (High Low)  so I can decompose clock and other stuff ;-)


Re: debouncing a switch (in hardware)

Brian McFarland schreef:

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Hi Brain,

Why don't you start messing around with the MAX II / EPM240. It comes
with an internal oscillator that can be used for debouncing. Additional
to this it has an schmitt trigger option on the inputs.

You can misuse the design example and steel the debouce:
http://altera.com/support/examples/max/exm-analog-encoder.html

Karl.


Re: debouncing a switch (in hardware)

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Hi Brain,

Why don't you start messing around with the MAX II / EPM240. It comes
with an internal oscillator that can be used for debouncing. Additional

to this it has an schmitt trigger option on the inputs.


You can misuse the design example and steal the debouce:
http://altera.com/support/examples/max/exm-analog-encoder.html


Karl.


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