I'm thinking of making a basic digital multimeter, using an Arduino. Any tips welcome.
I've Googled "how to make a digital multimeter" without a lot of success. Some hits are:
- How to use a digital multimeter
- How to buy a digital multimeter
- How to make a digital multimeter more useful
- How to choose a digital multimeter
- How to make an analog multimeter (?)
One site that I found had some brief descriptions (using an Atmega128) but his could only measure up to about 10V.
Now obviously you can measure up to 5V by just doing an analogRead, and probably up to 20V by going through a voltage divider first. But that assumes for one thing that you have the polarity around the right way, and most multimeters just show a "-" sign in the display if you have the leads backwards.
How do they do that?
One idea that springs to mind is to use a voltage divider, say 100/1, so that it could handle 500V. But then the resolution on low voltages would be poor.
Then I read about Instrumentation Amplifiers, which sound like they could be useful:
I don't quite get how the three op-amp instrumentation amplifier works - neither input (V1 or V2) is relative to ground but rather to each other. But somehow the two op-amps combine those into some sort of output. I suppose there is a common implied ground but that makes my head hurt a bit thinking about it. And I don't see how that handles negative voltages, except perhaps that they aren't negative if there is no ground.
Anyway, any suggestions or links would be appreciated, thanks.