guidance needed

Great tips thank you. I am working on a project now that requires sensing when 120VAC is present on 6 different wires. I have a bunch of Apple charging cubes and I was thinking of hooking those up to the 120volt lines and then sending 5 volts to the analog pins from the cubes when the power is on. Not very sophisticated but it seems to work. So far I have only tried one cube, and it works if connect all of the grounds. The project needs a total of 6. Are there any issues with having 6 charging cubes sending 6 separate 5 volt signals to the analog pins all sharing the ground with the arduino? Also is there a better way of doing this? I've looked a hall sensors and Non contact loop current transformers but I'm not sure if they will work and I need 6 total which would drive the cost of the project up. Also, I already have a box of those cubes.

The project is
I have a 6 burner range. I would like to have a string of LED lights change color when the burners are on, but only a section that is above the knob. When the gas knob is turned on it sends 120volts to the ignitor it stays ON until the knob it turned OFF.
I have the lights, and all of the other components working; it's the sensing of the knob position that is killing me.

I have good access to the wires themselves and a non contact way to sense power would be preferred.

Thank you in advance for any suggestions you might have. Sensing 120 volts seems to be a bit of an issue that doesn't have an easy answer.

What would be really cool is a way to sense if the gas is on but not lit then the lights could turn green until ignition and maybe sound a buzzer after 10 second of gas but no fire. The ignitor circuit can tell when there is ignition or not by completing the circuit from the striker to ground via the flame. I am only measuring 6 volts at the ignitor when it is striking (and I know its much higher than that!) and nothing when its lit and the circuit is completed. Maybe the ignitor would be the place to measure? How would you measure if the ignitor is grounded via the flame and not cook the arduino while it's striking? Not sure, thanks again.

Here is the component list-
Expansion Adapter - This is powered from a 12volt power supply
Charging cubes - Not all the same brand but similar to these

A page about flame senors

A moderator may want to move this topic....

A relay with a 120VAC coil is a little more straightforward than using power adapters. (A relay is an electrically-operated, electrically-isolated switch.)

You can also use an opto-isolator but the current-limiting resistor for the LED ends-up consuming about 2W (because of the voltage dropped across it) so you need higher-power resistor than "usual" with normal lower voltage LED circuits.

I'm surprised the voltage stays on when it's not generating a spark...

There are lots of easier to use lower-temperature solid-state heat sensors but you'll probably have to use a thermocouple for a flame. They put-out a very-low voltage that needs to be amplified and that can make them finicky.* You can buy pre-made amplifiers but you'd need 6 of them.

  • "Scientifically" thermocouples are super-precise because the voltage is defined by the physics of the dissimilar metals. But, the high-gain amplifier can have noise or drift and sometimes in scientific applications they have to be used with a zero-degree ice bath reference.



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a simple voltage divider would work to get a signal.

a simple AC-opto would work to get a signal.

since you are only consuming about 10mA, you do not need high power resisors. 1/4 watt would work and the current would be in the mA range.

they would be LIVE MAINS VOLTAGES, so would be REQUIRED to be enclosed and protected.

I have made such things with a simple 'repair' type of plug. the type you buy to put on the end of a lamp cord, or when you cut your extension cord with the lawn mower because it was left out and the grass got to high......

I have made these with LED's as nightlights in the old days.

to answer the question about non-contact.
go on e-bay and look at CT or Current transformers.
there are ones that are not much bigger than my thumbnail.
low current, under 10 amps if possible.

But, when I start my gas, it sends a pulse out, makes a spark then the voltage is removed.
you would need to make sure that your voltage is always present.
also, you would want to measure it directly at least one time, or get the manual and see if there is information in the troubleshooing section on what voltage to expect.

A second way would be to put a temperature sensor near the heat. Even a few inches away would detect the presense of a flame. since the flame temperature is over 1,000 deg F, you could assume that any temperature over say, 500 degrees means that there is a flame present. also, since you would be measuring radiated heat, some calibration would be required.

and of course, there are actual flame detectors for furnaces. also a candidate for detecting a flame

and for the wow-factor.
a remote temperature sensor could measure the bottom of your pot and reveal it's temperature.
would be interesting to know if you are simmering for a long time.

joke_mod = ON

so the parachutist jumps out of the plane and pulls the rip-cord........ nothing......
then he pulls the emergency rip-cord...... nothing.......
as he is falling, he sees something.... wait.... looks like a man..... coming up at him.....
he yells "hey- you know anything about parachutes ? "
the other guy yells back, " NO, you know anything about gas stoves ? "

joke_mod = OFF

a simple voltage divider would work to get a signal.

a simple AC-opto would work to get a signal.

since you are only consuming about 10mA, you do not need high power resisors. 1/4 watt would work and the current would be in the mA range.

If you are working with 120V mains, then 10mA through the current limit resistor with about 120V drop will produce;
120 * 0.01 = 1.2W, 1/4 W resistor would not work.
Tom... :slight_smile:

and then sending 5 volts to the analog pins from the cubes when the power is on.

If you just want an ON/OFF indication there is no need to use analog pins.


A hot burner should make loads of near-IR but.. where to put the detector?