Hello Guys
The ACS712 is wonderful to measure an AC Current up to 5A.
But how can I measure a small current from 0-200mA fullscale.
I haven't used the ACS712 before, but it would seem that you'd need to use an op-amp to amplify the signal using gain = 25 to get an identical signal span. The only potential problem is that the noise would also get amplified by 25X. See application 3 on page 12. Gain would be R3/Rf, so you could try making R3 = 24K (standard resistor value) for gain of 24.
EDIT: More information needed.
More information would be needed to determine an appropriate circuit.
A common method is to put a resistor in the circuit and use an opamp to amplify the voltage across the resistor to determine the current.
There is also an opamp circuit for converting current to voltage that introduces little series impedance.
Look for a current transformer (clamp on current measurerer thing). If you wrap the wire you are measuring, it will read 10x the current. So clamp one wire at 5 ma it picks up 5 ma. Wrap the same wire 10x it reads 50ma.
"I ordered a Adruino due"
3.3volt processor.
No good with 5volt ratiometric sensors like the ACS712.
Tell us what you want to measure.
The ACS712 might or might not be the right choice.
Leo..
To measure the ac current you need to convert it to a dc voltage to read it with an arduino.
What frequency is the ac? what is it's waveform? is it isolated from ground or at a high voltage?....
given these something could be devised.
regards
Allan
allanhurst:
To measure the ac current you need to convert it to a dc voltage to read it with an arduino.
Not always.
You could also sample a complete sinewave, and calculate current from that.
Leo..
More information required :
At what voltage and frequency are you measuring current
What is power factor of system consuming current (this doesn't affect current measurement but could affect what it is you are doing with the measurement.
What do you actually want to measure : peak, RMS or mean
Assuming it is TOTALLY isolated from any mains or line system you could use a dropper resistor to produce a 5 volt signal then feed this to a precision rectifier and then smooth out the signal to a DC measurement.