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switch debouncing

If you have that kind of induction then there is no choice but to use L-C-L T-lowpass into 2-way TVS into circuit, this bounds the outside world into something within the range of operation of the IC.

The ESD clamp diodes of G1 clamp the ESD attenuated by R2.

Nah- if you keep the diodes and make them Schottky, then almost no current goes into the IC, and in this case any IC input clamp current is circulating in loops , the positive going input diode current is a small fraction of what the output PMOS is pulling out of Vcc, and vice versa on negative going inputs, GND, and the NMOS pulldown- it may be a good idea to *add* a current limiting resistor in series with C if you keep the diodes- say R2/100.

Not the way to view it:-) The correct analogy is additional current draw induced in a mA circuit by placing a 1G in parallel with it- not much.

Reply to
Fred Bloggs
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At AC you have this- I don't see good and uncomplicated reason why the oscillation should not sustain itself: View in a fixed-width font such as Courier.

. . . . . . 5 | . | . +-------------+ | | | | . | | VT+| /\\ /\\ / \\ . | | | | / \\ | / \\ / \\ . | |\\ |\\ | VT-| \\ / \\ / \\ / \\ / . +-| o---| o---+-> | \\/ \\/ \\/ \\ / . |/ |/ | | | . | | | | . schmitts 0 +---+----+---+-------------------- . 1x 2x 3x etc... . . Tpd->

Reply to
Fred Bloggs

The main advantage of the 555 would be extremely precise thresholds compared to that logic Schmitt inverter and you can still use the Ganssle circuit. He wants 0.7R2C>=20ms so for C=0.47u R2=56K then R1 can be anything nominal compared to R2 like 10K. This makes the worst case delay 30ms at 1.1RC. The draw back is one sw/555 whereas you get three sw/HC14, or possibly six. View in a fixed-width font such as Courier.

. . . +-------------------+-------------+------< . | | | . | | | . | ------------- | . | | V+/RST | | . [10K] | | | . | | | | . | |THR OUT|------------->

. +--[56K]--+--+TRIG/ | | . | | | DIS| | . o === | |N/C | . -| 0.47U| | CON| === . o | | GND |0.1U . | | ---------- 555 | . | | | | . +---------+---------+-------------+------< . . . . . .

Reply to
Fred Bloggs

Well, that wasn't shown.

low pass input filter with R2. The low output R of G2 is vital to circuit operation.

Neither end of C is connected to ground; both ends are connected to semiconductors, and semiconductors are what's killed by esd zaps. 50 ohms won't impress a good arc, or G2 can be the IC that's killed. Of course, the transzorbs fix that problem.

One of my pretty firm rules is to never have semiconductors connected to the outside world, arcs included.

input and the C,R2 node.

This schematic seems to have all sorts of invisible parts. Good, that resistor definitely shifts the damage path toward G2.

not needed with large values >of R2

a miss trigger to propergate from G1 to G2.

of G2's output 50R and R2=1e5 we only need a 2000V input change to cross the 1V hytersis threshold.

Again, assuming R2 doesn't arc.

Well, if you analyze it carefully enough it should be OK. But simpler circuits have less hazards. Without the transzorbs, this one would be scairy.

John

Reply to
John Larkin

You want debounce. See....

Newsgroups: alt.binaries.schematics.electronic Subject: Switch Debounce (from S.E.D) - NoiseBlank-555-RC.pdf Message-ID:

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

formatting link
| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Reply to
Jim Thompson

I've seen switches with bounces 50 to 500x as long as yours.

--
 Thanks,
    - Win
Reply to
Winfield Hill

Sheeesh, Win, It's just an example, dredged from a noisy voltage signal application... change the RC already!

I have some EXTREME "debouncers" if anyone is interested.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

=_NextPart_000_0077_01C5D4AF.2B09E040 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

"John Larkin" wrote in = message news: snipped-for-privacy@4ax.com...

message=20

Reply to
Harry Dellamano

On Thu, 20 Oct 2005 03:50:39 +0000, Fred Bloggs wrote: [snip]

Nope. ;-)

Reply to
Mac

I'm not sure that could be called a debouncer- maybe more of a noise blanker. You have that known V1 clock and corrupt it with much higher frequency (1-V2V3/25). A switch debouncer does not have that luxury.

Reply to
Fred Bloggs

low pass input filter with R2. The low output R of G2 is vital to circuit operation.

input and the C,R2 node.

not needed with large values >of R2

a miss trigger to propergate from G1 to G2.

of G2's output 50R and R2=1e5 we only need a 2000V input change to cross the 1V hytersis threshold.

Did the OP say he was designing a wheel-well switch for the AirBus?

Reply to
Fred Bloggs

The sources are for illustration ;-) NOT "known V1 clock"... it's NOT a clocked system... look carefully before leaping for a change.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

I had a temperature switch that bounced forever. It was mounted in a tugboat, on the side of a diesel engine.

John

Reply to
John Larkin 

--
Sure!  see "Over-the-top debounce" on abse for a start.  I\'ve also
got \'em digital with counters, and in code.
Reply to
John Fields

See "NoiseBlank.pdf" on the S.E.D/Schematics page of my website for several different variations.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

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