I am trying to figure out how to build a very simple, cheap as possible digital ohm meter. Resistance is all i need it to display in a range from 0 ohm to 500 ohm. I would like it to be as small as possible. I have looked at using a pic micro controller to do this, But i am just not educated enough to figure it out on my own. I read the An512 ( implementing Ohmmeter/temperature sensor) and thought that this could be used to display the resistance value on an lcd screen. Any ideas on where i could find a tutorial or instruction on how to build what i need.
How precise are you looking to measure? For example, are you trying to measure to within a few ohms or down to tenths of an ohm? And are you trying to measure it in a DC or AC circuit?
If you’re looking for ‘a few ohms’ in a low voltage DC circuit and you’re planning on using a PIC, you could easily do it with a [voltage divider going to an analog input. That’s the first ‘simple’ solution that comes to my mind.](Voltage divider - Wikipedia)
It’s doesn’t have to be very accurate A tolerance of +/- 5 ohms would be fine. Its a dc circuit I beleive. I will have to look at it tonight and check.
Basicall i want to connect the ohm meter permately to my Potentiometer and have it display the resistance as I adjust the POT.
If your pot is in a circuit, you can’t just use an ohm meter to read the resistance as it’s energized. You’ll get really screwy readings if you do that.
I would say get a simple DC volt-meter and measure both sides of the pot and find the side that varies as you turn it. If the pot isn’t used to limit current directly, it’s probably in a voltage divider circuit and generates a voltage at that point which is read to an adc and used to adjust whatever it is this thing controls. If you can measure that voltage yourself you can use it to figure out where the pot is at any given time.
Definitely measure something else that you can relate to the value of that resistance. Like jotux said, measure the varying voltage across the two pins you’re using; it won’t affect your circuit much (especially if, as you said, the resistance is between 0 and 500 ohms, then the megaohm resistance of the voltmeter won’t affect a thing). I don’t know what type of pot you’re smoking … er … using, but if it’s a typical one, I would almost suggest measuring the other side of the pot and subtracting from the total resistance (I would guess 500 from your previous posts), if you really truly need that resistance.
I do have to admit, though, just the idea of building an ohmmeter sounds cool.