[sdiy] Semi-ot: bistable switch

[James Patchell]

If you are connecting the thing up like I suspect you would...well, even 
though it will work on paper...it won't work in reality...

The problem is contact bounce in the switch.  I am assuming you have the 
switch connected up to the clock input of the 7474 and the 7474 is set up 
to toggle on each positive edge transistion of the clock...

Well, because of the fact you have contact bounce...every time you push the 
button, you will get more that once clock transistion....so it becomes more 
of a coin toss than a toggle...you will need to come up with a way to 
debounce the switch...which will add a little more hardware.... :-(


At 04:59 PM 9/17/2004 +0200, Karl Ekdahl wrote:
>Hi all. I've been banging my head for a day now trying
>to do a simple bistable switch. one press and it's on,
>another press and it's off and so on, state indicated
>by a led. the actual push button will only be able to
>deliver a +5v signal while depressed and the switch
>has to be resetable. i've tried doing this with 7474's
>(i've got way too many of those) but haven't had any
>success. I need at least eight of these in a small
>space. could anyone help me? this is newbie problem, i
>know, but it's making my head cook.
>
>thanks
>
>Karl

         -Jim
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