I have 0-5 V analog value coming in, and I need to convert it to a high or low 5V digital signal. Essentially, I need to create a 1-channel A/D converter. The idea is that when my analog voltage goes above a certain threshold, it will set the digital output high, and vice-versa. I saw something about being able to do this with op-amps, but I don't remember where I saw it. I also want to do this without using a microcontroller. Any ideas?
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Typically you'd use a comparator for this. Or you could make a transistor version with a long-tailed pair.
A Schmitt-trigger would be a nice solution for a 0 to 5V input:
But you pointed to an op-amp circuit...
Here's the idea. An opamp as a comparator with logic output.
It's worth reading through ADI's application note on that (source for the picture).
Their Conclusion is accurate in my opinion and worth bearing in mind:
"In conclusion, although op amps are not designed to be used as comparators, there are, nevertheless, many applications where the use of an op amp as a comparator is a proper engineering decision. It is important to make an educated decision to ensure that the op amp chosen performs as expected"