buttondebounceencoder
I'm trying to figure out the way of debouncing encoders and tact buttons with Schmidt triggers, but I'm confused with 2 existing schematics:
simulate this circuit – Schematic created using CircuitLab
Which of those two options are right?
Values are shown for 5.0V inputs level, would the be the same for 3.3V?
Or for 3.3V I should use another Schmidt trigger IC (not 7414)?
Thanks in advance!
I would highly recommend hooking a scope (hopefully you have one or can get your hands on one to use) up to your switch. I have seen a student's project that had a bounce on their switch that went from 5v down to -5v up to 4v down to -3v then up to 2v then back down to 0v. When we looked at the current draw on a scope there were some a very very large spike.
In his particular case it was very very much needed for him to debounce his switch in hardware.
However, on the other hand, I have seen switches that have a much smaller effect that could easily just be removed in software.
You do need to weigh your options though. If you have a very complex amount of firmware, adding the overhead on both you as a programmer and the cpu usage may not be worth it and you would be better off to just add a little bit of hardware. Now on the other hand, if you are trying to get costs and size down, you will want to remove as much hardware as possible and do it all in firmware if you can.
Note: You can replace the op-amp assembly with a schmitt-trigger inverter or buffer, to make your life easier. Anything with some input hysteresis will work.
Best Answer
The first is the better option. Notice that the second circuit does not provide the output gate with the intended 0 V ground when the switch is closed. It is supplied a low level voltage through a voltage divider.
However, when the switch is closed in the first circuit, the gate's input is pulled down to ground, but slowly- as the cap discharges. This is what you want.
Edit also read all the comments. I agree with mkeith that, if this is for a microcontroller project, consider denouncing in firmware.
And jonk is right (as he often is) that there may be better, prepackaged, options depending on your needs.
Edit: 3.3 V will work fine with a 7414, provided you supply the IC with 5 V nominal on the VCC pin to power the chip. The resistors are up to you. The values of the resistors and capacitor affects the capacitor's charge/discharge time. Higher values provide more denouncing, but increase the wait time allowed between subsequent triggers. You might also want to add a voltage follower as an output stage.
For Example:
and...
Regarding your 7414 question in the comments: