# Detecting AC voltage (contactless)

Discussion in 'General Electronics Chat' started by Kenjutsu, Feb 24, 2015.

1. ### Kenjutsu Thread Starter New Member

Jul 26, 2010
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Hello everyone,

I want to build a circuit that can signal an Arduino that an AC voltage is present in a cable or not. I am not interested in measuring the AC volt/current. Since I have no experience working with AC circuits, I would prefer a contactless solution.

I am clueless on how to proceed

2. ### MikeML AAC Fanatic!

Oct 2, 2009
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What is the AC voltage?
120/240V?
50/60 Hz?

3. ### Dodgydave Distinguished Member

Jun 22, 2012
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Last edited: Feb 24, 2015

Jul 26, 2010
6
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230V 50Hz

5. ### MikeML AAC Fanatic!

Oct 2, 2009
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Here is the safe way of doing it:

Get an old 4Vdc to 5Vdc (no higher) cell-phone charger that looks like this:

Cut off the output plug, and wire it to a load resistor, like 470Ω or 1KΩ. Check the output voltage across the resistor with a DC Voltmeter. If 5Vdc or less, wire the 0V output end of the resistor to the Arduino Vss (Gnd), and wire the +5V output end to an Arduino Port pin.

6. ### Dodgydave Distinguished Member

Jun 22, 2012
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see circuit in post #3, contactless detection

7. ### MikeML AAC Fanatic!

Oct 2, 2009
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Won't work if no current is flowing in the sensed circuit.

Jul 18, 2013
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Do you need contact-less voltage detection even in the absence of current?
Max.

Jun 22, 2012
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10. ### Kenjutsu Thread Starter New Member

Jul 26, 2010
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Thank you for all the replies. Like I said, I have never worked with AC powered circuits before. Basically what I want to know is: is there AC power in the cable, yes or no.

Jul 18, 2013
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Here is one from another site.

Max.

cmartinez likes this.
12. ### MikeML AAC Fanatic!

Oct 2, 2009
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Good reason to use the cell-phone charger...

13. ### KMoffett AAC Fanatic!

Dec 19, 2007
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What kind of cable are you working with?

Ken

14. ### Kenjutsu Thread Starter New Member

Jul 26, 2010
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It is a standard "household" cable that is rated at 20A. I think just to clarify further: I want to monitor several mains appliances/devices to see of they are still receiving AC power from the grid.

Something like: TV power ON; Fridge power ON; Fan power OFF; and so on. The idea is to determine whether there is a general power failure (blackout) or just one circuit breaker tripped.

Jun 22, 2012
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16. ### Kenjutsu Thread Starter New Member

Jul 26, 2010
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This looks interesting. I'm sure I'll be able to open it up and hack to provide input to the Arduino. At that price point, it is probably cheaper than a DIY solution as well.

Jul 18, 2013
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In many cases these electricians neon type testers require that the unit be held by the operator for them to operate via earth leakage, the return path is a very minute current through the body.
Max.

18. ### alfacliff Well-Known Member

Dec 13, 2013
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I have at home a stud finder with wireing detector. it is for findi9ng studs in walls and live circuits in walls. it uses a coil like the previous diagram (numbedr 11) and works by induction. even a circuit drawing no current will show its there. ou might try a small ausio transformer, remove the Bridge from it and the open end of the E shaped core should pick up ac induction.

Jul 26, 2010
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