Go Down

Topic: Measuring voltage over a resistor (Read 1 time) previous topic - next topic

soulid


liudr

If you power arduino with a battery, you can do that measurement. If you use USB, your arduino gnd is tied to the common ground, you will damage arduino. Not sure about ac adapters. They seem to be floating or are they? How large are these resistors you drew. If they are not very large, you can build another voltage divider to get the voltage lowered. But the resolution of arduino will suffer if you lower the voltage to 0-5V since your variation will be scaled down from 0,7-1,4 to about 1/3 of that. Can you swap the locations of the two resistors? That'll be truly useful.

retrolefty

Quote
If you power arduino with a battery, you can do that measurement.


How? The arduino board must still share a common ground with the voltage source driving the constant current driver so I don't see how that solves the 'too high a voltage for an arduino AI pin, no matter how you power the arduino board?

Lefty


LarryD

The way you have it in your schematic isn't the same as how you have it wired up!

liudr


Quote
If you power arduino with a battery, you can do that measurement.


How? The arduino board must still share a common ground with the voltage source driving the constant current driver so I don't see how that solves the 'too high a voltage for an arduino AI pin, no matter how you power the arduino board?

Lefty




If I use a battery, I would attach floating arduino gnd to the junction between the two resistors and measure the junction between the left resistor and power supply. If the constant current is small, then the junction between it and resistor will have low voltage. Otherwise it's as high as 10-14V. There's no numbers to decide which way it is.

Go Up