Hello
I was attempting to purchase an inverting Schmitt trigger for button denouncing, but I have managed to order a hex inverting buffer.
Are these similar/the same? I couldn't quite work out (with google) what the difference was between the two.
Can they both be used for debouncing? (with an RC circuit)
Any help appreciated.
They are both inverting so that's the similarity.
A schmitt trigger gate has a more defined and wider input threshold than a non-schmitt trigger gate. A ST gate typically turns on at 70-80% Vdd and turns off at 20-30% Vdd - so it has better immunity.
They both can be configured for debouncing purposes.
but I have managed to order a hex inverting buffer.
A hex inverting buffer just means there are six in the one package.
You can get hex Schmitt trigger buffers, like the 74LS14 or hex non Schmitt trigger buffers like the 74LS04, exactly what chip have you ordered?
Schmidt trigger has large hysteresis, so it can take a noisy signal at mid-rail without amplifying the noise back to logic levels. Slowly varying inputs will always pick up noise in a digital circuit and a standard gate/buffer has lots of gain. (output of an RC low-pass debounce filter is an example of slowly varying for instance)
A standard buffer has no hysteresis and can generate lots of switching spikes on a slowly varying input.
You can add hysteresis to a CMOS non-inverting buffer by adding a resistor between input and output, assuming the driving impedance is not low. ~20% positive feedback ought to work nicely (10k feedback, 2k2 input resistor...)
Debouncing can be done in software if you don't want to add extra hardware - you just ignore any change that doesn't persist for several ms (try 10ms in first instance)