Debouncing multiple switches

[ADWSystems]

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]

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]

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

 

[ADWSystems]

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

Yes. Each button needs to be debounced individually.

 

[ADWSystems]

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

Those are cool. Too bad I don't have a way of dealing with SMT parts.

 

[Mr RB]

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]

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

 

[vne147]

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]

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

 

[ADWSystems]

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

 

[vne147]

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.

 

[ADWSystems]

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?

 

[vne147]

74F273A Datasheet pdf - Octal D flip-flop - Philips

 

[Mike_2545]

Oh I thought you wanted a toggle feature, here is one that just de bounces the contacts:

 

[vne147]

Oh I thought you wanted a toggle feature, here is one that just de bounces the contacts:

I think this trumps everyone else's ideas.

 

[ADWSystems]

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.

 

[Pommie]

Oh I thought you wanted a toggle feature, here is one that just de bounces the contacts:

I think that is a programmed 16F628 chip. I can supply the code if anyone wants it.

Mike.

 

[ADWSystems]

74F273A Datasheet pdf - Octal D flip-flop - Philips

The 74ALS576 might be easier to deal with. It has bus structured input and output pins.

 

[ADWSystems]

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?