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Debouncing multiple switches

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I has a series of pushbutton switches that I need to denounce. There's no microcontroller/processor, so software isn't an option. Placing a 555 on each switch isn't really practical. The switch is SPST, leaving the NAND input option (that requires SPDT) off the table. Is the only option left, the RC net fed into an inverter?
 

vne147

Member
I has a series of pushbutton switches that I need to denounce. There's no microcontroller/processor, so software isn't an option. Placing a 555 on each switch isn't really practical. The switch is SPST, leaving the NAND input option (that requires SPDT) off the table. Is the only option left, the RC net fed into an inverter?

Will you need the capability to push more than one button simultaneously?
 

Roff

Well-Known Member
Have a look at MAX6816/17/18. They are, respectively, single, dual, and octal debouncers.
 

Mr RB

Well-Known Member
Just use a large RC filter on each input. You won't get much smaller or cheaper than 1 R and 1 C per pin. And you get some extra ESD protection etc which is always handy on pushbuttons. ;)
 

Mike_2545

Super Moderator
This chip can take a momentary pushbutton input and de-bounce 8 switches, it is a 18 pin dip package
 

vne147

Member
This chip can take a momentary pushbutton input and de-bounce 8 switches, it is a 18 pin dip package

If I'm understanding the datasheet correctly, this IC toggles the output. So a single button press will be debounced to 25 ms but then the output of the IC will stay high until the button is pressed again. So, it has the effect of turning a momentary pushbutton into a latching push button.
 

Mike - K8LH

Well-Known Member
Yes, those outputs are toggled. Do you want the outputs to simply follow the input with 25-msec propagation delay?
 

vne147

Member
I don't know about vne147, but I need them to follow the input.

I don't know about me either. Have you thought about using a D flip flop and just clocking it slower than the debounce period? It wouldn't be perfect but it might be good enough. You could use 2 flip flops in series if you needed it to be better.
 
I was thinking about that last night. I think they make, but I haven't had a change to look for, a octal latch chip. 8-inputs with 8-outputs latched on a CLK signal. What does anyone else think about this idea?
 

Mike_2545

Super Moderator
Oh I thought you wanted a toggle feature, here is one that just de bounces the contacts:
 
Are there any other sources than Jameco? They have a $25 minimum order and they don't stocking any of the other parts I need for the project.
 
If I used a 555 timer with a 25ms one-shot and a 16v8 PLD, do you think I would be able to accomplsh the same thing as the EDE2008?
 
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