Schmitt trigger weird behaviour

[SwengX]

Hello,

I have a project where I use this exact schmitt trigger to debounce a pushbutton. When I push the button nothing happens at the digital pin on the  Arduino. I think it just floats. Actually, I use an embedded Atmega328. When I press the Atmega a bit with my finger, the state of the pin changes from 0 to 1 or vice versa regardless of the state of the pushbutton. So far, this looks like a floating pin. I measured the voltages, the schmitt trigger output pin was ok (5V), and I made a continuity test from the output to the arduino digital pin and it was also good. However, I can't measure 5V on the arduino digital pin. The voltage just goes away?! Then, I noticed that when I connect my multimeter between the schmitt trigger output and GND, everything works fine. What causes this? I hope it is nothing serious because it is quite hard to modify the circuit on the pcb.

[Smajdalf]

Try to resolder the Schmitt IC - at least the output pin. I seems you get it working everyone you press it to the PCB improving contact.

[dlloyd]

If you want the Arduino input to be normally low (high when button pressed) then perhaps your circuit connections are like this?

[6v6gt]

You can, of course, debounce a button purely in software. Something like if you get a button press, ignore further activity from that button for the next , say, 100mS.