Re: [CAD_CAM_EDM_DRO] debounce circuit

On Fri, 02 Jan 2004 20:24:55 -0000, you wrote:

>What is a "debounce circuit" as it relates to a digitizing probe,
>and does anyone have a schematic for the electronically challenged?

Problem: A switch, being mechanical, will not make a clean contact,
it makes a contact then bounces. Modern (i.e anything at all)
digital circuitry is fast enough to record each of those
contacts/bounces as a separate contact.

A debounce circuit will clean all this up, and is often a cross
coupled R/S flipflop.

One way is to cross couple two 7400 series gates in an RS (reset/set)
flipflop. Wire pin 1 to pin 4, wire pin 3 to pin 4. Run pins 2 and
pins 5 individually to 2.2 K ohm resistors, connect the other end to
+5 volts. Run pins 2 and pins 5 to the NC and NO arms of a SPDT
switch, ground the switch arm.

Any output taken from pin 3 or pin 6 will be debounced. Assuming that
you wired it exactly as described, you will find that pin 3 is high,
then goes low on a contact (stays low as long as the probe is in
contact). Pin 6 will be low, and go high for the same amount of time.

You can do the same with a 7474 flipflop, a 74LS279 (iirc, it's
designed for that, 4 in a package), or any other flipflop that has
direct set and direct reset inputs.

You can also wire up the other side of the 7400 to do the same thing
for another probe, if you want.

Harvey

>
>Thanks
>Steve
>
>