Switch Debounce 1

[Malakai]

For a variety of reasons, im looking for a way to easily debounce 8 PTMs without using schmitt triggers. Does anyone know of a good way of doing so?

Kris/Maior

 

[nbucska]

What is a PTM?
<nbucska@pcperipherals.com>

 

[cbarn24050]

its a TLA .

 

[nbucska]

You mean AFA (Another F^%$@#^\* Abbreviation ) ? <nbucska@pcperipherals.com>

 

[BrianG]

I agree with nbucska - I don't know what yhe heck a PTM or a TLA is either!

However, assuming your inputs must be logic signals since you don't want to use Schmitts, how about using the Motorola MC14490 digital Contact Bounce Eliminator chip. This has 6 separate digitally integrated de-bounce circuits per chip driven from an internal common clock. The clock frequency - and hence the eventual de-bounce time period - is simply set by one small external capacitor. This chip is CMOS and works on supply rails from 3 to 18V and I have used it in many applications and so can vouch for its effectiveness.

Enjoy!

 

[Malakai]

TLA: Three Letter Acronym
PTM: Push-to-Make (of the switch variety)

BrianG, that IC sounds to be exactly what I need, thankyou very much.

Kris

 

[47gandalf]

Please note that the MC14490 is now a product of ON Semiconductor. The Motorola web site thinks MC14490 is a serial to parallel converter.

The debounce circuit sounds like a winner. I'm going to get the ON data sheet and look to use this part.

Thanks for bringing it up.

 

[biomedicalEng]

you can also use S-R latchs which are very inexpensive and 6 of them are integrated in a single chip and also most of the semiconductor making factories have these chips.

S-R latchs are great for debouncing a push button!

 

[BrianG]

I have found from bitter experience that the &quot;classic&quot; S-R latch debounce circuit cannot be guaranteed to work with all switch types. Some switch types can actually bounce back and forth for a few milliseconds, so that you get pulses from both contacts alternately. This makes the R-S latch useless, as all you get is a stream of fast pulses from both outputs until the switch finally settles down. (.....and before anyone suggests it, having to add capacitors to the R-S latch to get rid of spikes defeats the object!)

 

[felixc]

If you want to fine tune your circuitry, or add functions or integrate more stuff into a single-chip, you can do the keyboard debounce and encoding using a microcontroller, like a zilog Z8encore whose smallest models sell for under $2. and the complete development system sells for $40.