Hello again,
Just for the sake of completion of this topic, I found a solution in the web for the initial problem: A circuit that detects if an AC appliance is ON/OFF.
Anyway, I'll only use this schematic if my solution with the non-contact voltage detector. I have ordered (still waiting) an isolated power supply and I'm hopping to solve the problem with it.
Cheers,
Joaoabs
Hello again,
So I finally got my new isolated voltage sensor. I build a test circuit in a breadboard, did some tests (touching with the loose end of the resistor on some low-powered cables - my 20w soldering iron) and it worked.
So I soldered the circuit in my board and strategically positioned the sensor near one cable that don't have current flow when the appliance is off.
Unfortunately, it didn't work. It seems this sensor only works when close together with both cables (neutral and live). The output varies too much and is not reliable.
Any idea of what may I be doing wrong?
Circuit:
Photo:
Thanks,
Jooabs
sonnyyu:
There are a lot ways detect AC, but OP's way is the most coolest way.
Have you tried this? LEDs don't survive high reverse voltages very well, and this circuit has very high reverse voltages appearing across the LEDs in the optoisolators.
I don't see how voltage detection does any good, anyway. You want to know if the appliances are drawing power. That requires measuring current.
No, I haven't try it. I also suspected that the high-voltages would be too high for these components.
What I tried was the circuit I posted today. Conceptually, I don't see why it shouldn't work, but the sad true is that id doesn't and I'm back to square one.
Any suggestion of something that could work?
Thanks,
Joaoabs
Well, 12k on 220Vac dissipates a bit over 4W, so you'd need 10W resistors, not 1/8W.
Why are you still trying to detect voltage? You have already said that relays may be on, hence presence of voltage, but the appliance may still not be drawing power. Measure the current.
Hello,
Indeed, measuring the current was my first approach, but it din't work well (initial post on this topic).
How would you suggest to measure current?
The problem is that I need a sensor that is flexible enough to detect the current flow of 20w to 2000w.
Thanks,
Joaoabs
Unless I'm missing something, the ACS712 for 5amp can handle 30amps of current. You won't be able to measure the 30amps, you will only know that it's more than 5amps. Because you only want to know if current is flowing, this should work for you. If you need to measure the different currents, add a shunt across the ACS712. The datasheet does list the resistance of the ACS712. Use the AWG wire chart to make your shunt. xfeet of yGuage is zOhms. A shunt equal to the ACS712 will allow for measurement of 10amps. A shunt equal to 1/3 of the ACS712 will let you measure 20amps.
I would use a photo-transistor for most of the detections, at least for all lamps.
It is a 1 component solution with little risk of getting dangerous voltages into the Arduino.
The hardest thing is to shield stray light from the photo-transistor, but to check that you can drop the relay and see if it still detects light. 
Use two LEDs in series, 1 for a visual indicator, the second enclosed in black heat shrink tubing with the photo transistor, photo diode, or photo resistor inside. I might just fill the tubing with clear RTV and then insert the led and photo device from opposite ends. That should give you good isolation. Or you could just use a 6 pin opto isolator with a LED in series for a visual indicator.
hello, i'm newbie..
i'm just wanna ask..my project need to use voltage sensor for rate 240VAC
is there any method or link to me create a voltage sensor??
thank you for your feedback..
in addition,i'm only use nano arduino for my project