RC Filter For Switch Debounce

I am using an AutomationDirect DL-06 with a H0-CTRIO to retrofit to a Bindicator. I will be getting pulses from a micro switch on the Bindicator at about 10 hertz. I was bench testing using a toggle switch in place of the micro switch and noticed that I was getting about 10 debounce pulses every time I flipped the switch, leading to a false pulse count.

I am going to build a simple passive RC circuit to try and filter anything over 15 hertz. This is a pretty low frequency and would like some insight. I will have a 1.4k resistor and 1000nF capacitor later today to test with.

The high speed counter card does not have any filtering capabilities.

zmanvortex said:

I am going to build a simple passive RC circuit to try and filter anything over 15 hertz.

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if this is the corner frequency then the signal will be reduced by -3db but you will still get some signal above 15 hz. A first order filter has a gentle roll off.

zmanvortex said:

This is a pretty low frequency and would like some insight. I will have a 1.4k resistor and 1000nF capacitor later today to test with.

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15 Hz is low and your filter is not low enough to match 15 Hz.
f = 1/(2*PI*R*C) which is about 113 Hz for the values you provided.

zmanvortex said:

The high speed counter card does not have any filtering capabilities.

Click to expand...

What you really need is some D flip flops. Better yet a switch that doesn't bounce. It would be worth the money. This will be a pain in the a$$ trying to get the filter just right. Others on the forum have bought higher order filters that have sharper rolloff than a simple first or RC circuit.

Just wondering... are you using an actual rotory Bindicator?

Thanks Peter. I have discovered with a scope set to trigger that my debounce has a 10-14khz debounce and also a 3-4khz debounce element to it. I had an old 30nF cap and a 1.5k resistor that I tested. This setup eliminated the 10-14khz frequency but allowed the 3-4khz through.

Of course this is on a toggle switch and I can guarantee that the microswitch debounce will behave much differently. I think I should be able to filter anything above 30hz and be ok.

I don't think the sloped drop off will affect the count but I will find out for sure later today and let you know.

I think with the proper cap sizing I can get the filter to do enough for the application.

rdrast, This bindicator lowers a weight to the material. A cam triggers the microswitch on it's way down. Once the weight hits the material a slack switch triggers which raises it back up.