Re: slightly off-topic: switch de-bouncing

on 03 09 01 18.03, Marc Alexander at marc@wolfems.com.au wrote:

>
> There's something up with this, the LS02 is actually a NOR gate, and
> the LS04 is an inverter. I guess the IC's are labeled backwards?
>
Sorry, the inverters are an LS04, and the gate is an AND (LS08).

> You definitely want to change the inverter to an LS14, which is a
> 'Schmitt trigger' input, it has hysteresis on the input.
> Meaning that if the output is low, it will take eg. <1V to make it go high,
> and if the output is high, it will take eg. >3V to make it go low.
> This dead band gives excellent noise rejection as the input needs
> to move eg. 2V for the output to change.
> I've used 1V and 3V as examples, the data sheet for the IC has exact values.
>

Okay. I replaced the LS04 inverter with an LS14. The results are a little
better, but not much different.

> As Rodger said, 1uF or maybe more is good for the caps also.

I'm about to replace the caps, but I don't know how to read the -)|- symbol.
Which side of the cap should I tie to ground? The existing caps (.1µf) are
not polarized.

> The output isn't a 'pulse', it will stay low while both buttons are held down
> together.
> (is this the way it's supposed to work?)

Yes, the output stays high while both buttons are pressed.
I'm relying on the data book's statement that the counter only reads a
rising edge. Right now, the counter pulses on button press *and* release. I
think that's because of bounce. Hopefully, once the bounce is gone, the
double triggering will be gone, too.

corrected diagram:

>>> +5v
>>>
>>> | |
>>> \ \
>>> / / 1K
>>> \ \
>>> / / LS14
>>> | | 220 Ohm (Schmitt triggers) ____
>>> Start 1 []------+-----/\/\/\/--+--------|>o-------| \
>>> | | |LS08|-- output
>>> Start 2 []---------+--/\/\/\/------+----|>o-------|___/
>>> | | (AND)
>>> - - 1µF
>>> - -
>>> | |
>>> === ===
>>> = =
>>>

-- 
Anthony Ramos________
600 SE 39th Ave., # 3  \__ aramos@ele-mental.org .. aramos@hyperreal.org
Portland, OR 97214      \___ information design .. multimedia production
(503) 236-6303           \____________interactive art .. image synthesis
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