# Amplifying and Reading a 0-1 V signal into Arduino

I'm trying to read the (0~1V) output of a current transformer (CT) into the 10-bit ADC input of an Arduino Nano. The CT is sensing the L wire carrying 120V at 60Hz.

Current Transformer Specs:

• Input Current: 0~30A AC
• Output Mode: 0~1V
• Non-linearity: ±1%
• Build-in sampling resistance（RL): 62Ω
• Turn Ratio: 1800:1

Since the Arduno accepts analog input of 0-5V, the CT's output have to be scaled to make full use of the 10 bits.

Additionally, I think the CT's output is a AC waveform, so it would vary between -1V and +1V. If this is correct, I would need to bias the output by AREF/2 (5V/2 = 2.5V) by diving the 5V and GND rails equally using a potential divider made out of 2 resistors.

How should I scale the 0-1V to 2.5V, assuming the output vary between -1V and 1V? Is there a solution that will both amplify the CT's output signal and bias it as well?

The circuit I'm using currently looks like

and a plot of the analogRead() values is shown below, where the x-axis represents the index number of the ADC sample, while the y-axis represent the ADC value (0-1024). Sampling rate is about 9 kHz (110us per sample). Peak-to-peak difference is about 55 samples, giving us a frequency of 165 Hz.

• arduino.cc/en/Reference/AnalogReference That leaves solving the DC bias, which depends on frequency and waveform (bandwidth) which you didn't mention. Commented Mar 22, 2014 at 17:23
• @jippie Updated question with the current I'm sensing: 120VAC at 60Hz. Commented Mar 22, 2014 at 17:38
• Before trying to get any circuit configuration advice you will need to change the state of every "I think" and "I believe" in your question to "I Know". Before that is done all supposition is a full waste of time. Commented Mar 22, 2014 at 18:33
• @MichaelKaras The specsheet states that the CT has an output of 0-1V. But I am under the impression that a CT outputs will vary between positive and negative values. Is it possible to tell without using an oscilloscope? I only have a Fluke 179 multimeter and a Arduino. Commented Mar 22, 2014 at 18:41
• What sampling rate are you using - what is the scale on the x axis? What current was flowing at the time in the AC wire? Commented Mar 22, 2014 at 19:39