Hi all,
I have done myself the circuit below in order to gauge the energy consumption in my house and gladly it worked fine, but a question concerning its operation has come up, and i have been digging through the internet and haven't found a clear answer for this yet.
I was wondering if someone could explain to me why it's necessary to have a VRef of 5V?
Is this voltage value supplied by the arduino itself or it also comes from the sct reading?
tks in advance
A current transformer measuring AC outputs positive and negative voltages. An Arduino pin can only work with positive voltages (0-5volt for a 5volt-logic Arduino). Lifting 'ground' of the current transformer to 2.5volt ensures that the pin only sees positive voltages. The signal now swings around this mid-voltage bias point, which can be removed with code.
Leo..
The VRef required depends on the value of the burden resistor (33Ω here),
the SCT013 has a 2000 : 1 ratio so 100 Amps in = 0.05A out. 0.05 * 33 = 1.65 V + (1/2 supply Volts) = 4.15V. So you need a VRef greater than that.
Which MCU board are you using?
Forgot about the peak of 1.65volt?
Leo..
No, it's 2.33345237792V. Why didn't you question the 33Ω burden resistor with a 5V supply?
Peak to peak voltage output voltage of the CT at 100A with 33ohm burden is 4.666904755831214volt, which just fits in 5volt Aref.
Leo..
Thank you very much, guys!
Only one question that remains is, what is the capacitor used for?
The way i see it, just the divider resistors would work to offset the voltage level.
A capacitor smooths out rapid voltage changes (of the 5volt supply).
That said, it's sort off unwanted with a ratiometric A/D. You want mid-voltage to follow Aref changes closely. I would probably have used 100n instead of 100uF. But someone drew that a long time ago, and it's never going to be changed/deleted from the internet.
Leo..
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