[Solved] Best way to detect if Breaker Switch is ON

Hi

I need to detect if a coffee machine breaker switch is ON or OFF, with an Arduino Uno.
The voltage on the breaker switch is 220Vac
What is the best way to do this?
I tried with a non-invasive current sensor (SCT-019), but I can't seem to detect any current flow.
I know i could do this with a AC-> DC transformer, but it seems a bit overkill since I only need to know if the switch is open or not.

Any suggestions?

Thank you

Opto isolator with the current limited by a capacitor - likely 0.22uF rated 330VAC with a series current-limiting/ protective resistor of about 2k7 - and either a bridge rectifier, or a reverse diode across the isolator LED or an AC isolator with back-to-back LEDs internally.

If the heater is always on when the breaker is on you could use a thermocouple.

Keith, i'm looking at a coffee machine, not a heater. Although the machine does get hot in some places, it's not a good solution in this case.

Paul__B, thanks for the reply. Lots of information in just one paragraph.
Any idea if there's any "of the shelf" circuit doing what you described?

Thanks

taxus:
Any idea if there's any "of the shelf" circuit doing what you described?

Oh, there will be a few around, ranging from the "low end" devices implementing exactly what I described, to fully integrated commercial modules.

Searched on "220V digital input".

I have used these a while back:
http://www.fairchildsemi.com/ds/MI/MID400.pdf

Paul__B:
Opto isolator with the current limited by a capacitor - likely 0.22uF rated 330VAC with a series current-limiting/ protective resistor of about 2k7 - and either a bridge rectifier, or a reverse diode across the isolator LED or an AC isolator with back-to-back LEDs internally.

I would also go with optocupler. Gives you total isolation between the high volatges in the coffemaker and your sensitive Arduino.

Another way would be to build your own optocoupler. Is there a light that turns on when the coffemaker is on? Then place a light sensor on ,or close to, that light and connect it to your arduino. Viola! =)

Tobbera's suggestion gave me a great boost to solve my problem.
Material:

  • One of those cheap 240Vac "leds" (see image)
    http://tinyurl.com/mbys9ah
    -A simple fotoresistor (i had a few around)
  • A 10K resistor

The led terminals are connected to the coffee machine breaker switch (240Vac).
The led and the fototransistor are optically connected (and secured using simple black isolator tape).
The 10k resistor forms a voltage divider with the fotoresistor, which is connected to the analog in of the Arduino

Secure and cheap solution.

Thank you for all the replies.

taxus:

  • One of those cheap 240Vac "leds" (see image)

Looks suspiciously like a neon indicator.

This thread needs a photo! :smiley:

Old fashioned way: Tape a CDS cell to a NE lamp, connect one lead of the lamp to the return side of the power cord, connect a 10M ohm resistor to the other lead of the lamp, connect the other resistor lead to the appliance feed side of the main switch (your breaker), connect one side of the CDS cell to +5 V on the arduino, connect the other CDS cell lead to an analog in on the arduino in a voltage divider config. determine the analog level when the switch is on. in your software, then the analog in is at, or above, the above found analog value (less some very small amount), the switch is on, the CDS cell conducting and resistance lowered, thus imbalancing the voltage divider's condition when the switch is off. You cann't get much more caveman than that.....