Schmitt Buffer/Trigger with Encoder and buttons - Inverting...

hi all,

In a middle of a PCB design and wanted to make things proper with my buttons and rotary encoder. So apart from RC filter, i would also like to include Schmitt Triger for a proper signal of the encoder and buttons.
After researching the matter for a bit, i am still a little confused on "inverting" Schmitt Triger.

My schematic looks like this, except i use 10k resistors and 1uF tantalum caps:

So a few questions:

  1. I would need to convert (end debounce) signal from encoder and buttons, so i was thinking of getting this one:
    74HC14D
    However, this one says "inverter", and i am aware that i can also get inverted signal output, but here i need non inverted signal. So the question is, would this one work for my case?
  2. If i do have inverted signal, would that mean simply swapping the contacts on the switch to work as non inverting?
  3. 74HC14 has 6 IN/OUT pins, can i use 2 for encoder and remaining 4 for 4 buttons? All on one IC? Or is it better to separate for whatever reason?
  4. I can use 74HC14 for mechanical toggle switches as well? I see no reason why not.

Many thanks,
Alek

elcrni:
My schematic looks like this, except i use 10k resistors and 1uF tantalum caps:

You must really hate that encoder. Subjecting them to 1µF of capacitance! That's gotta hurt.

However, this one says "inverter", and i am aware that i can also get inverted signal output, but here i need non inverted signal. So the question is, would this one work for my case?

For an encoder that will not matter. After all you're just interested in the edges. At most you have to reverse the direction detection in ode, that's it. Do look up and understand how an encoder works and how it's signal is read!

  1. 74HC14 has 6 IN/OUT pins, can i use 2 for encoder and remaining 4 for 4 buttons? All on one IC? Or is it better to separate for whatever reason?

Of course you can. But... Those 1 µF caps... The pain felt by the encoder will be passed on to the power bus... Not that a second chip helps reduce that pain. 47nF is really more than enough!

At least remember to connect a 100nF ceramic cap (not tantalum or electrolytic or film) to the Vcc pin of each and every chip. Placed as close as possible to that pin.

wvmarle:
At least remember to connect a 100nF ceramic cap (not tantalum or electrolytic or film) to the Vcc pin of each and every chip. Placed as close as possible to that pin.

Thanks wvmarle!
There was a mistake in my original post, what i meant was 0.1uF rather than 1uF...
Also, for those ceramic caps, not sure i got it, to use them on VCC/GND but as close as to what pin? Encoder/switch pin entering or exiting Schmitt IC?

Many thanks,
Alek

I thought I was clear: “the Vcc pin of each and every chip”. Chip = IC. Standard decoupling caps. The encoder of course doesn’t need it, that’s just a pair of switches. The 74HC14 needs it. One per chip.

Mind that for fast encoders you have to reduce the 100k pull-up or the cap doesn’t charge fast enough. With 100nF cap and 100k pull-up you’re limited to about 50 pulses per second.

wvmarle:
Mind that for fast encoders you have to reduce the 100k pull-up or the cap doesn't charge fast enough. With 100nF cap and 100k pull-up you're limited to about 50 pulses per second.

Still way more than i can achieve by hand turning the knob. I will use 10k anyway for pull-up and 220 for signal line.
Many thanks!
Alek

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