Detecting AC voltage drop

Hello,

I'm working on a fog machine controller and I took apart my fog machine's remote.
I already have a relay installed to switch it on/off, but I would like to be able to tell if the fog machine is heated or not.
The remote has/had a status indicator light, which has 230VAC going through when the fog machine is heating and 10VAC when it's heated.

What's the easiest way to determine this huge voltage drop with an Arduino?

I want to replace the indicator light with a normal LED. (With the LED connected to the Arduino, of course).

What's the easiest way to determine this huge voltage drop with an Arduino?

Using an opto isolator.

A resistor and capacitor can reduce the voltage to allow an LED to be lit from the mains. There are lots of circuits that will do, google for them.

I don't want to light the LED directly, because I want to be able to detect the status (heated/heating) with software. Is that also possible with an opto-isolator?

I don't want to light the LED directly

Yes you do. The LED is inside the opto isolator you need to light it up in order to detect the signal on the arduino. You do not see this LED but the circuit needs to light it up.

Oh you mean the LED inside the Opto-isolator... I thought you meant a separate one.

I was looking at the PC817 opto-isolator/optocoupler, but I'm not entirely sure how it would be connected. Would you be willing to help me out? I bet you have a lot more experience than me and I don't want to damage anything (or hurt myself) because I'm dealing with high voltage.

We were just discussing a similar circuit here:

Give me a few minutes, I'll get a specific recommendation for the capacitor.

I'd try this capacitor:

It will drive the optoisolator's LED at about 7mA and according to the following, it should operate safely at 230V.
http://industrial.panasonic.com/www-data/pdf/ABD0000/ABD0000PE111.pdf

Thanks for your reply.

So I'll need a 0.1?F capacitor rated for 630VDC, a PC817 opto-isolator (or similar), a diode (any specific one?) and resistor (what value?).

And how would I connect the collector-emitter side of the opto-isolator to the Arduino?

artaex:
Thanks for your reply.

So I'll need a 0.1?F capacitor rated for 630VDC,

Yes but don't just use any old capacitor, make sure it's rated for 230VAC, which is why I linked the Panasonic document above.

a PC817 opto-isolator (or similar),

Not familiar with that one, see the schematic in the other thread that I linked above, it uses a 4N35.

a diode (any specific one?)

1N4148, see the schematic in the other thread that I linked above.

and resistor (what value?).

1K?, see the schematic in the other thread that I linked above. 1/4W should do it.

And how would I connect the collector-emitter side of the opto-isolator to the Arduino?

See the schematic in the other thread that I linked above. The idea is to generate interrupts at line frequency, so use attachInterrupt() or similar.

I'd be a bit concerned that your fog heater has 10 volts on it, when it is not running.

michinyon:
I'd be a bit concerned that your fog heater has 10 volts on it, when it is not running.

I never said the heater has 10V on it. The indicator light has 10V when the fog machine is heating.