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Simplest, cleanest, push button debouncer?

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Terry Pinnell
Guest

Wed Sep 12, 2018 6:45 pm   



Is there any consensus on the neatest circuit to take a noisy push
button signal and output a clean rectangular pulse?

Searching through my ancient (paper) files I found dozens, but my
scribbled notes on many show that when tested I'd found lots failed,
allowing some noise to reach the output. My starting assumption is a
simple CR filter in front of a Schmitt. But before I head for the shed
and start bread boarding I'd much appreciate any recommendations please.

Terry, East Grinstead, UK

Dimitrij Klingbeil
Guest

Wed Sep 12, 2018 6:45 pm   



On 2018-09-12 18:54, Terry Pinnell wrote:
Quote:
Is there any consensus on the neatest circuit to take a noisy push
button signal and output a clean rectangular pulse?

Searching through my ancient (paper) files I found dozens, but my
scribbled notes on many show that when tested I'd found lots failed,
allowing some noise to reach the output. My starting assumption is a
simple CR filter in front of a Schmitt. But before I head for the
shed and start bread boarding I'd much appreciate any recommendations
please.

Terry, East Grinstead, UK


The good old 555 timer works nicely in this application. It has a very
wide hysteresis (from 2/3 of Vcc to 1/3 of Vcc) that makes the circuit
immune to noise and unwanted re-triggers. There is a push-pull logic
output available as well as the open-collector "discharge" one, and
everything apart from the 3 timing-related passives is integrated. For
CMOS logic compatibility from 1.5 V supply and up, there's the LMC555.

Jasen Betts
Guest

Wed Sep 12, 2018 10:45 pm   



On 2018-09-12, Terry Pinnell <me_at_somewhere.invalid> wrote:
Quote:
Is there any consensus on the neatest circuit to take a noisy push
button signal and output a clean rectangular pulse?


If a microcontroller is involved do it it in software

If the button is dual throw wire NO/NC across the logic supply and put a
small capacitor on the output (C)

> My starting assumption is a simple CR filter in front of a Schmitt

yeah, thats the third option.

--
ت

George Herold
Guest

Thu Sep 13, 2018 2:45 pm   



On Wednesday, September 12, 2018 at 12:54:50 PM UTC-4, Terry Pinnell wrote:
Quote:
Is there any consensus on the neatest circuit to take a noisy push
button signal and output a clean rectangular pulse?

Searching through my ancient (paper) files I found dozens, but my
scribbled notes on many show that when tested I'd found lots failed,
allowing some noise to reach the output. My starting assumption is a
simple CR filter in front of a Schmitt. But before I head for the shed
and start bread boarding I'd much appreciate any recommendations please.

Terry, East Grinstead, UK


If you can do a double throw switch then there is a config that uses
an SR flip flop. (And others.. see AoE3.)
With a single pole I think you are stuck with a long
time delay... (Some RC thing ~10's of milli seconds.)

George H.

amdx
Guest

Thu Sep 13, 2018 8:45 pm   



On 9/13/2018 2:25 PM, amdx wrote:
Quote:
On 9/12/2018 11:54 AM, Terry Pinnell wrote:
Is there any consensus on the neatest circuit to take a noisy push
button signal and output a clean rectangular pulse?

Searching through my ancient (paper) files I found dozens, but my
scribbled notes on many show that when tested I'd found lots failed,
allowing some noise to reach the output. My starting assumption is a
simple CR filter in front of a Schmitt. But before I head for the shed
and start bread boarding I'd much appreciate any recommendations please.

Terry, East Grinstead, UK


 Here's one I came up I came up with that worked in a very noisy
product we had. I've posted it many times never got any response, good
or bad.
It uses an SCR.
http://photobucket.com/gallery/http://s395.photobucket.com/user/Qmavam/media/Debouncejpg.jpg.html


                           Mikek

I guess I didn't read enough, it outputs a pulldown pulse.


amdx
Guest

Thu Sep 13, 2018 8:45 pm   



On 9/12/2018 11:54 AM, Terry Pinnell wrote:
Quote:
Is there any consensus on the neatest circuit to take a noisy push
button signal and output a clean rectangular pulse?

Searching through my ancient (paper) files I found dozens, but my
scribbled notes on many show that when tested I'd found lots failed,
allowing some noise to reach the output. My starting assumption is a
simple CR filter in front of a Schmitt. But before I head for the shed
and start bread boarding I'd much appreciate any recommendations please.

Terry, East Grinstead, UK


Here's one I came up I came up with that worked in a very noisy
product we had. I've posted it many times never got any response, good
or bad.
It uses an SCR.
> http://photobucket.com/gallery/http://s395.photobucket.com/user/Qmavam/media/Debouncejpg.jpg.html

Mikek

asdf
Guest

Thu Sep 13, 2018 11:45 pm   



On Wed, 12 Sep 2018 17:54:46 +0100, Terry Pinnell wrote:

> My starting assumption is a simple CR filter in front of a Schmitt.

Yup, that's probably the simplest and cheapest effective way.
But if you need more buttons to be debounced, a uC solution might
be more scalable and simpler so that the filter could be
implemented in software virtually using no components other
than the minumum necessary to have the uC run.

Rick
Guest

Fri Sep 14, 2018 11:45 am   



"asdf" <asdf_at_nospam.com> wrote in message
news:pnem1h$1184$1_at_gioia.aioe.org...
Quote:
On Wed, 12 Sep 2018 17:54:46 +0100, Terry Pinnell wrote:

My starting assumption is a simple CR filter in front of a Schmitt.

Yup, that's probably the simplest and cheapest effective way.
But if you need more buttons to be debounced, a uC solution might
be more scalable and simpler so that the filter could be
implemented in software virtually using no components other
than the minumum necessary to have the uC run.


Look at the MC14490. Works great.

asdf
Guest

Fri Sep 14, 2018 11:45 am   



On Fri, 14 Sep 2018 05:25:58 -0500, Rick wrote:

> Look at the MC14490. Works great.

Never heard of that chip, looks interesting. Thanks.

John Larkin
Guest

Fri Sep 14, 2018 6:45 pm   



On Thu, 13 Sep 2018 21:49:37 +0000 (UTC), asdf <asdf_at_nospam.com>
wrote:

Quote:
On Wed, 12 Sep 2018 17:54:46 +0100, Terry Pinnell wrote:

My starting assumption is a simple CR filter in front of a Schmitt.

Yup, that's probably the simplest and cheapest effective way.
But if you need more buttons to be debounced, a uC solution might
be more scalable and simpler so that the filter could be
implemented in software virtually using no components other
than the minumum necessary to have the uC run.


A uP doesn't need hardware or software debouncing. Just sample the
switch state 10 times per second and use what you see.

It could use emi/esd protection, but that's just one capacitor.




--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

whit3rd
Guest

Fri Sep 14, 2018 10:45 pm   



On Thursday, September 13, 2018 at 5:56:39 AM UTC-7, George Herold wrote:
Quote:
On Wednesday, September 12, 2018 at 12:54:50 PM UTC-4, Terry Pinnell wrote:
Is there any consensus on the neatest circuit to take a noisy push
button signal and output a clean rectangular pulse?

If you can do a double throw switch then there is a config that uses
an SR flip flop. (And others.. see AoE3.)


Yep, that's a good 'un. There's also Hall switches (or used to be) from
Cherry, in keyboard-mountable form, that give good clean output
and don't fail from dirty contacts. I'm not seeing any inexpensive such
items nowadays, but have a box of the old ones somewhere.

Phil Hobbs
Guest

Sat Sep 15, 2018 1:45 am   



On 9/13/18 3:25 PM, amdx wrote:
Quote:
On 9/12/2018 11:54 AM, Terry Pinnell wrote:
Is there any consensus on the neatest circuit to take a noisy push
button signal and output a clean rectangular pulse?

Searching through my ancient (paper) files I found dozens, but my
scribbled notes on many show that when tested I'd found lots failed,
allowing some noise to reach the output. My starting assumption is a
simple CR filter in front of a Schmitt. But before I head for the shed
and start bread boarding I'd much appreciate any recommendations please.

Terry, East Grinstead, UK


 Here's one I came up I came up with that worked in a very noisy
product we had. I've posted it many times never got any response, good
or bad.
It uses an SCR.
http://photobucket.com/gallery/http://s395.photobucket.com/user/Qmavam/media/Debouncejpg.jpg.html


7 parts is a lot for a debouncer. An RC lowpass and a tinylogic Schmitt
will work fine.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Phil Hobbs
Guest

Sat Sep 15, 2018 3:45 am   



On 9/14/18 6:25 AM, Rick wrote:
Quote:

"asdf" <asdf_at_nospam.com> wrote in message
news:pnem1h$1184$1_at_gioia.aioe.org...
On Wed, 12 Sep 2018 17:54:46 +0100, Terry Pinnell wrote:

My starting assumption is a simple CR filter in front of a Schmitt.

Yup, that's probably the simplest and cheapest effective way.
But if you need more buttons to be debounced, a uC solution might
be more scalable and simpler so that the filter could be
implemented in software virtually using no components other
than the minumum necessary to have the uC run.

Look at the MC14490. Works great.



Four bucks in reels! Six 1-cent caps, six 0.3-cent resistors, one
8-cent 74HC14.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Terry Pinnell
Guest

Sat Sep 15, 2018 12:45 pm   



amdx <nojunk_at_knology.net> wrote:

Quote:
On 9/13/2018 2:25 PM, amdx wrote:
On 9/12/2018 11:54 AM, Terry Pinnell wrote:
Is there any consensus on the neatest circuit to take a noisy push
button signal and output a clean rectangular pulse?

Searching through my ancient (paper) files I found dozens, but my
scribbled notes on many show that when tested I'd found lots failed,
allowing some noise to reach the output. My starting assumption is a
simple CR filter in front of a Schmitt. But before I head for the shed
and start bread boarding I'd much appreciate any recommendations please.

Terry, East Grinstead, UK


Here's one I came up I came up with that worked in a very noisy
product we had. I've posted it many times never got any response, good
or bad.
It uses an SCR.
http://photobucket.com/gallery/http://s395.photobucket.com/user/Qmavam/media/Debouncejpg.jpg.html


Mikek

I guess I didn't read enough, it outputs a pulldown pulse.


Still an interesting circuit that I mean to try, thanks.

Terry Pinnell
Guest

Sat Sep 15, 2018 12:45 pm   



Phil Hobbs <pcdhSpamMeSenseless_at_electrooptical.net> wrote:

Quote:
On 9/13/18 3:25 PM, amdx wrote:
On 9/12/2018 11:54 AM, Terry Pinnell wrote:
Is there any consensus on the neatest circuit to take a noisy push
button signal and output a clean rectangular pulse?

Searching through my ancient (paper) files I found dozens, but my
scribbled notes on many show that when tested I'd found lots failed,
allowing some noise to reach the output. My starting assumption is a
simple CR filter in front of a Schmitt. But before I head for the shed
and start bread boarding I'd much appreciate any recommendations please.

Terry, East Grinstead, UK


Here's one I came up I came up with that worked in a very noisy
product we had. I've posted it many times never got any response, good
or bad.
It uses an SCR.
http://photobucket.com/gallery/http://s395.photobucket.com/user/Qmavam/media/Debouncejpg.jpg.html


7 parts is a lot for a debouncer. An RC lowpass and a tinylogic Schmitt
will work fine.

Cheers

Phil Hobbs


True, but it always feels wasteful using only half a 14-pin IC, like a
4013 for example. And time-consuming terminating the unused inputs.

But my interest in the SCR circuit is mainly because I have a bunch of
ancient, low-power SCRs, maybe 40-50 years old.

Terry, East Grinstead, UK

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