Advice: best way to detect gas hob is on


Putting in a new kitchen this week. I have a rangehood that can be controlled using rf 315mhz. I want the rangehood to turn on automatically when i use the hob.

My hob is a gas hob with electronic ignition. The dials only have a very thin line on them so i think it would be difficult to use optical recognition on them.

This is a photo of the ignition circuit.

Here is a photo of the hob, it has a dent so i am waiting for replacement.

I was something about using an infrared camera perhaps, the other option would be an ambient temperature and above the hob temperature probe but I’m not sure if that would be very reliable.

Just wondering if there are any thoughts. I have a spare pi 3b as well as nodemcu chips that could be used.

Can I wire into the ignition circuit or will the power that goes into the ignitors blow the gpio?

Are there any tiny rf transmitters with button batteries that i could install inside the knobs and trigger when they are pressed down.

Not sure how you would do this.
The Electric ignition is defo not gonna work as it would only be on manually to light the gas flame, it never stays on.
Maybe some flow sensor like a smapee

No doubt it will.

You might be able to install a temperature sensor in your rangehoob.
If the temperature increase by 5 or 10 degrees in less than 5 minutes, it would be an indication that someone is cooking. But not sure if the temperature difference would be enough to be detected.

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A few of these appropriately positioned (to prevent damage by spills or over heating) would do the trick, they’re 3.3V logic compatible too:

They’re available on eBay from china for even less if you can wait for delivery.

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Really? Automations are great, but IMHO this is OTT. If you are lighting the hob, you are right there and able to start the extractor by pressing the button.

It’s not like turning the AC on when it gets too hot, or starting the heater when you leave work.

I just don’t think every damn thing needs automating!

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Sometimes it’s more the challenge and the process than the end result that matter.

If it’s just about the result, I agree, this won’t be very practical. Anyway you’re in front of the rangehood, and you’ll still have to increase/decrease the speed according to your need.

And you might not want to leave it on when you’re just simmering something or heating up something.

Also the maintenance might be annoying in a cooking environment.

The flame sensor proposed by @tom_l seems to be quit a nice solution, just have to see if this is made for a big open flame or also work 1 meters from a small flame covered by a pan. Also this detect light emitted, which is not necessarily a lot coming from a hob, a candle emitting much more light with a smaller flame.

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Oh I agree about the challenge!

With a nice new hob in your revamped kitchen, where is one going to put those flame sensors and pass the WAF test?

What about a humidity/smoke sensor up in the extractor? When venting steam/smoke gets too high, turn it on then - and if that is not enough, turn up to next level.

It actually detects infra-red radiation. From reading a couple of projects that use it, the digital output can detect a lighter flame at a distance of up to 30cm and it has to be direct line of sight. So a pot on top of the hob could be a problem unless the the sensor is mounted at quite a low angle. The analogue output type modules can detect a small flame up to 90 cm but this would be more complex to interface to a raspi.

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Carbon Dioxide sensor perhaps? Monitor a rapid increase in CO2 levels.

@kiwijunglist how did this go? I am looking to do the same, and just tried the flame sensors, and they seam to react to an orange flame rather than a blue one.

Why not a strategically placed temp sensor? Fire is hot. :smiley:

Had a baby instead so plan abandoned