Hello , I have a Arduino Uno, and i want to read voltages values in arduino , i use Oamp to reduce the voltage but i can't do it, because arduino don't read negative values.
When i open Serial port i see something like this:
You may be able to convert the AC to DC (bridge rectifier & cap), then you read the peak AC. If you want to convert that back to RMS I think there is a formula, that I don't have on the tip of my tongue at the moment.
I think the RMS is peak X 0.707.
I want to read a voltage source for exemple with 10V, so i reduce this 10 V to something that arduino can read, and after i convert this value to a "real voltage" again.
But arduino don't read negative values so how i can do it?
If that is a 10 volt AC rms, it will be about 1/3 higher peak voltage. Do you want to measure the peak or the RMS (normal reference for AC) ?
I assume this is coming out of a step down transformer that is plugged into the wall? Is your wall outlet 110V or 220 volts ( really does not matter tho).
No opamp needed.
Use a voltage divider with two 10k resistors.
One from +5volt to analogue-in.
One from analogue-in to ground.
Then connect the AC voltage to analogue-in with a capacitor.
If you use a capacitor and a resistor in series, you also have a voltage divider.
Use 24k and 10-100uF (+ Arduino side) to measure 10V AC without clipping.
You will measure a value of ~512 without any input.
You must take many samples to see the waveform.
Leo..
One from +5volt to analogue-in.
One from analogue-in to ground.
Then connect the AC voltage to analogue-in with a capacitor.
If you use a capacitor and a resistor in series, you also have a voltage divider.
Use 24k and 10-100uF (+ Arduino side) to measure 10V AC without clipping.
Leo..
With respect Wawa, I can't see how that would work.
I still think a bridge rectifier with a cap (10mf) would give a peak reading, and that can be calculated to an RMS value. I could be wrong tho.
If it's always a sine wave, just find the peak and multiply by 0.707. Otherwise, you can sample the waveform at a high sample rate and calculate the true-RMS value.
Superimposing AC onto 2.5volt DC is an easy way to measure the whole AC wave.
Downside is that you have to take many samples to know what the wave looks like.
True RMS measurement is possible.
A passive diode rectifier is non-lineair. Try to measure 0.5volt in that 10volt range.
But ok if you want to measure the mains voltage. That stays always near maximum.
Another way is an active (opamp) rectifier.
I suppose it all depends on what you want to measure.
Audio, mains, ??
Leo..
A passive diode rectifier is non-lineair. Try to measure 0.5volt in that 10volt range. But ok if you want to measure the mains voltage. That stays always near maximum.
That's a good question. Is the OP trying to measure an ac voltage derived from the main, or some voltage from a whales whistle, etc. ?