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how to test a debounce filter

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nicky.r

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Hello,

I have to verify/test the functionality of a debounce filter with a time constant from 10 to 255ms.
Could you please give sugestions on how to do this test.
 

Hi;

Only an idea (USING a microcontroller):

Write a simple interrupt routine to sense the key pressing.
It must be as short as possible: only increments a byte var (counter) and sets a bit var (a flag)

Outside:
first clear the counter and the flag
init and enable the IT

then wait for the flag in a loop
press the key now
if the flag is set: exit loop
then delay say 200 mS
then read the counter
then stop the test program (or try again : - )

If your debouncing circuit (hw RC filter) is working as well, the counter must be 1 (one)
else it will be greater as 1 because of the contact's bounce..


What do you think?
zuisti
 
Hi,

Thanks for your helpful suggestion.I believe that the debounce time of a keypress is 10 ms.How can I give an input whoes debounce time is more(say 200ms) ?,inorder to test the filter time constant range of 10ms to 200ms. How can I vary the debounce time of the input.

Thanks
 

nicky.r said:
I believe that the debounce time of a keypress is 10 ms.How can I give an input whoes debounce time is more(say 200ms) ?,inorder to test the filter time constant range of 10ms to 200ms. How can I vary the debounce time of the input.
Click to expand...

Hi;
The suggested program is for test only (it's a measuring program, NOT a
software debouncing !!!!) And it's working in range 0...200 mSec. You can
easily increase this range: simply use a bigger delay after the loop.

You have a hardware debouncing circuit (a simple RC filter), right?
In this case you can vary the filter time constant as usual, for example the
increasing of the resistor value causes a greater time constant ...

Try it out: without RC filter you will get 5-10 counts (or more) using the program.

BTW a key bounce time is NEVER longer as 30 mSec (it's usually 5-10 mSec).
 

Hi,


I meant to ask if I can vary the bounce time of the Keypress.But as you said, it is some fixed value which is normally not greater than 30ms.So can I give some input other than a keypress whoes bounce time is close to 250ms.

Thanks a lot
nicky
 

Yes, you can. For example with a gated pulse (burst) generator circuit:

!_!_!_!_!_!___________________________
<..burst..>
 

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