AVR-Chat

Some designs were implemented way before that.  This one is from 1976, 
when the MC14490 was a buck and a half and there were no 
microcontrollers to speak of...at least not economically available.  
When 1 customer orders 25 boards every 3rd year or so, and has about 5 
repairs a year, it isn't worth even reworking the artwork for the board 
to save 4 bucks.  When the chips become obsolete we may have to do 
something different.  In business, we have to make these kinds of 
decisions about old designs...I believe they call them "mature" designs 
these days.

New designs is another story.  An 8 pin Tiny controller for less than a 
buck has about done away with many of the 555 timer applications.


REB


np np wrote:

>I am amazed that this type of IC exists.
>I was writing key debounce software in 1984.
>
>www.ckp-railways/pcbcad21.htm
>
>
>"Roy E. Burrage" <RBurrage@bellsouth.net> wrote:                                  Motorola, now ON Semiconductor, also has/had the MC14490 for switch 
> debouncing.  However, at 5 bucks a piece the last time I bought any for 
> a control board I haven't taken the trouble to re design, it's much more 
> cost effective to write a few lines of code to do the same job in new 
> designs.
> 
> REB
> 
> Adam wrote:
> 
> >A couple of years ago I ran into this with an 8051, and my solution
> >was to simply wait for 20ms. 
> >
> >The initial button press would cause the interrupt routine to
> >activate. The micro would then wait for 20ms (doing other stuff in the
> >meantime of course!), and re-check the interrupt at the end. If the
> >interrupt was in the same state, then it was a legitimate button press
> >(and not induced noise/etc), and therefore the program should act
> >accordingly. Remember as well that when the button is released the
> >noise will be present as well, something that bit me on the posterior
> >before I took it into account. (Ouch! That took a little while to
> >find...."why the !@#$%^&@$^% isn't this $!%^%$@^ working?!?!?".)
> >
> >You may also wish to consider some IC solutions out there, I think
> >(from a hazy memory) that Maxim/Dallas have a keypad decoder chip that
> >debounces and decodes the keypress for you, making life a heap easier.
> >
> >Good luck.
> >
> >Adam.
>  
>


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