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Potentiometer value with ADC
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admiralk:
I keep flip-flopping on whether the pot value matters, or not, for the rate of change when used with an ADC.

Part of this project involves making a digital clock, and I want to use a pot to set the time. Since one turn is one turn and 0-255 is 0-255, it seems to me that what ever value I use will not effect how fast the number changes. I keep trying to convince myself that using a larger pot will make the numbers change slower, however. For hours, 0-12, I do not expect a problem. For minutes, 0-59, on the other hand, it seems that it might be difficult to settle on the right number if it is changing at the same rate. Or maybe that the hours would be too slow. I am getting nowhere fast listening to myself. I have almost convinced myself, now, that the only way I am going to accomplish this is to go with a multi-turn pot. Could someone please set me straight?
Ian.M:
If you wire the pot as a true potentiometer, the value has no effect on the unloaded output voltage provided the supply can provide enough current for the track resistance and the current at that supply voltage is within the pot's ratings.  However, when loaded, if the pot track resistance is greater than twice the maximum input resistance that the ADC is specified to work with, accuracy will be degraded.  Also if there is a large capacitance at the pot wiper, and you use a high resistance pot the voltage at the wiper may lag behind the physical pot movement by enough to be disconcerting or to make it difficult to adjust.
ogden:

--- Quote from: admiralk on August 08, 2019, 09:05:46 pm ---I have almost convinced myself, now, that the only way I am going to accomplish this is to go with a multi-turn pot.

--- End quote ---

Clock with multi-turn pots to me sounds like tool of torture. Why don't you use rotary encoder(s) instead?
floobydust:
You can scale the A/D so the pot goes from 1-12 or 0-59. Just dial in the value you want.
Or, less than half counts down, over 1/2 rotation counts up, with a dead zone in the middle.
Ideally a rotary encoder with built-in pushbutton switch would be the easiest UI.
admiralk:
Hmmm, I never bothered to look up what a rotary encoder was until just now. If I understand right, I could get away with a single one and just change the code depending on which number needs to change. It also sounds like I can easily adjust it to get the resolution I want. It would also mean that I could avoid buying new micros that have an ADC. I think I need to look into that a bit more.

Research time it looks like. Thanks all so far.
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