Boiling water detector - Page 1
Forum section: electronics / projects

author: brossler
author_rank: Newbie
timestamp: December 28, 2015, 06:00:55 pm
content: Hi,I would like to create device that detects boiling water. Point of this device is that you put it into pot with water while cooking and once it starts boiling, it starts beeping.I want to use termistor rated from -40 to 150 °C. Idea is to place main circuitboard outside the pot (so that I dont need to deal with overheating main circuitboard and making it waterproof). From this board, two wires would go inside the pot and on its end, there would be only the termistor.My worries are if the wire can handle 100 °C. I have no experience with this so I dont know what to look for (what kind of wire sleeves etc.). Since it will be placed in "food", it also should not release any toxic chemicals.Thanks for advices

author: w3amd
author_rank: Regular Contributor
timestamp: December 28, 2015, 06:09:44 pm
content: It's a bit complicated because water contains impurities which change the boiling point and the atmospheric pressure changes the boiling point.The most feasible might be to use sound detection in the water.John

author: Kalvin
author_rank: Super Contributor
timestamp: December 28, 2015, 06:11:49 pm
content: Just measure the temperature change of the water. When it boils, the temperature will not rise any more.

author: brossler
author_rank: Newbie
timestamp: December 28, 2015, 06:31:46 pm
content: Thanks, I will try both end see what works better.but what also concerns me is if I can put regular wire into boiling water. Not sure if it damages wire isolation. Any experience with that?

author: SeanB
author_rank: Super Contributor
timestamp: December 28, 2015, 06:34:53 pm
content: Easiest is to get an already enclosed thermistor in a stainless steel sleeve, with a lead made from a high temperature resistant plastic. Then simply set the boiling point to be 95C, which will be close enough for most places that are not at massive elevations. For the high altitude areas simply lower the set point. Boiling is not really important, you just want to be warned it is getting close. Many of the ready made thermistor probes are going to be able to withstand short immersion in 100C water, and the cabling will be PVC, so it should be kept clear as it typically melts at 70C. You can get high temperature insulation for there though.

author: moya034
author_rank: Regular Contributor
timestamp: December 28, 2015, 06:35:46 pm
content: Look for wire with high temp silicone insulation. It can work in temps in excess of 150 C.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 28, 2015, 06:38:14 pm
content: You'll also want food safe insulation.Tim

author: moya034
author_rank: Regular Contributor
timestamp: December 28, 2015, 06:39:54 pm
content: Quote from: T3sl4co1l on December 28, 2015, 06:38:14 pmIs that actually a thing? I've heard of insulation being rated for Plenum's but I don’t recall seeing a food safe specification.

author: m98
author_rank: Frequent Contributor
timestamp: December 28, 2015, 06:42:10 pm
content: Quote from: Kalvin on December 28, 2015, 06:11:49 pmThat's the right answer. For the wiring just use halogen-free silicone cable. To seal the sensor, you could use "sugru".

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 28, 2015, 06:54:28 pm
content: dT/dt is a pretty poor way to tell. How do you know if it's boiling or just simmering? The sensor just sitting there on the table at room temperature would detect boiling, too.I'd think a piezo sensor would be pretty reasonable, at least if the user isn't jamming some loud heavy metal...I wonder if a self-heating sensor would be reasonable. It becomes suddenly very much easier to create a bubble of steam when the bulk reaches boiling. Consider a pair of thermistors, one which is unheated (self heating < 1C), and another which is held at a fixed temperature above the other, say 5-10C. The amount of power required to develop that temp rise will jump discontinuously (I think) at boiling. Geometry will be important; if the hot thermistor is placed in a small cavity where it can develop a bubble (say, just inside the end of a plastic tube), the effect will be particularly strong.Fouling will be a strong concern, especially with anything self-heated, if this is to be used with any kind of food.Also, assuming the purpose is food preparation. If it's a non-food-safe process, it might not matter; then again, the condition of boiling might not matter either (just add a steam vent, and dump in enough excess heat to keep some boiling off). So I don't know what your intended application is.Tim

author: Kalvin
author_rank: Super Contributor
timestamp: December 28, 2015, 07:00:36 pm
content: Quote from: T3sl4co1l on December 28, 2015, 06:54:28 pmOf course it needs to measure absolute temperature as well, but the temperature change (actually lack of temperature change) is the detection criteria.Possibly one could use non-contact sensing like in those IR temperature meters.

author: tszaboo
author_rank: Super Contributor
timestamp: December 28, 2015, 08:21:46 pm
content: You could measure the temperature above the water. If the water is not boiling, it will be significantly lower, while the water vapor will be quite close to 100.

author: calzap
author_rank: Frequent Contributor
timestamp: December 28, 2015, 08:40:07 pm
content: I think simmering is boiling, just at a low rate of water to steam conversion. I you want to detect a specific rate of steam production, it's a much tougher problem. Plateau-ing of the temperature versus time curve is probably a good way to go, but there needs to be a delay at the start and little tolerance at the end. At the start, temperature inside pot may not rise very rapidly because exterior of the pot is heating first. Later on, as water leaves the pot as vapor, solids remain behind, solute concentration increases, and boiling temperature rises. The more soluble solutes there are at the outset or if cooking the food causes release of solutes, the more marked the effect.There are lots of electronic cooking thermometers on the market. Most have a stainless steel probe, and they come with probes of varying lengths and diameters. For some, the digital readout is on the end of the probe; others have a heat-resistant wire between digital readout module and probe. Should be possible to hack into the digital readout (some may have a digital output port). Might be possible to stuff a MCU in the readout case to evaluate temp vs time. I have a feeling this problem has been solved multiple times for industrial applications, like food processing plants.Mike in California

author: brossler
author_rank: Newbie
timestamp: December 28, 2015, 08:53:53 pm
content: Thank you all for suggestions.I will probably drop the idea of putting termistor into boiling water, i will try cheaper solutions first with parts I have. I like sound sensor solution, also I will try putting termistor above water and record values and see, if anything useful can be read from it.To elaborate what I am doing:My father works from home and because he doesnt want to wait till water starts boiling (when he prepares lunch), he goes to his work room. So he needs something that would notify him the water started boiling. Since I am interested in electronics, learning new things, and I like working on projects like this, he asked me to come up with something.So I split it into 2 parts: First detecting boiling water (which is this thread about) and Second is "alarm" (most likely wire running to the work room with speaker/piezo one its end). Some enhancements into the future like wifi connectivity are also feasible (yet maybe a bit overkill).

author: Paul Moir
author_rank: Frequent Contributor
timestamp: December 28, 2015, 08:56:53 pm
content: Quote from: calzap on December 28, 2015, 08:40:07 pmYes, normally with stainless steel thermowells welded into the sides of tanks or installed within process piping via a sanitary pipe fitting. Loose probes are sometimes used, but all I've seen were essentially a thermowell with the wire end being non food contact, and usually plugged with epoxy.I'm interested to hear what the OP's requirements really are, since a novel solution might be much better. Perhaps you could do it acoustically by picking up the nucleate boiling and alarming after that. Or with a manometer setup. Or even optically?

author: IanB
author_rank: Super Contributor
timestamp: December 28, 2015, 09:16:08 pm
content: The traditional solution to this problem is a kettle with a whistle. When the water boils the whistle screams. My grandmother had one.http://youtu.be/qEe5kwgpdq8

author: brossler
author_rank: Newbie
timestamp: December 28, 2015, 09:22:11 pm
content: I know about this solution, IanB. It is simple clever solution, but unfortunately it is quite hard to cook potatoes in it and also it needs to notify someone who is two walls apart.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: December 28, 2015, 10:05:08 pm
content: Personally I like NandBlog's idea for a practical beginner's project. If you have a thermistor already then you can it's wiring in silicone. The real food contact stuff will be catalytically cured but even some of the hardware store stuff will say something like "occasional food contact" as the ingredients are rather innocuous.Otherwise I would get a cheap thermometer with a metal probe and throw away the thermometer part. The trouble here is that they usually use thermocouples in them rather than thermistors, so they aren't as beginner friendly. I'm presuming you can't make a closed end stainless tube. They're not much work if you have a metal lathe or a TIG welderAcoustically would be interesting since it could possibly sit beside the stove. But it'll require some research and may never work.

author: SL4P
author_rank: Super Contributor
timestamp: December 28, 2015, 10:11:27 pm
content: Is your dads sense of smell ok?The smoke from a boiled dry pot of potatoes will alert him slightly after they have boiled!Does he nod off occasionally while the potatoes are cooking?This sounds like areally good example of an open loop control system... not criticising, but there are better ways - unfortunately, I they're usually more expensive.That old adage stands. If a job is worth doing, then it's worth doing properly.This gadget us not needed one day per year... it will be used many times before the kitchen catches fire.

author: edavid
author_rank: Super Contributor
timestamp: December 28, 2015, 10:26:38 pm
content: You could take the thermostat out of a cheap rice cooker.

author: moya034
author_rank: Regular Contributor
timestamp: December 29, 2015, 12:28:32 am
content: Quote from: Paul Moir on December 28, 2015, 08:56:53 pmI had no idea what a thermowell was so I googled it. Then that made me think, many automotive coolant temp sensors are very similar in design. You could have someone weld a bunghole to the side of a stainless steel pot:Then I also realized, they do have a ready made device that does what you want, only catch is you can't get water in the area where the wire comes out of the probe, but it is long enough you might be able to rig something up somehow:edit:

author: w3amd
author_rank: Regular Contributor
timestamp: December 29, 2015, 03:42:02 am
content: Quote from: brossler on December 28, 2015, 09:22:11 pmThe vapor pressure of the water will also change when it gets to boiling. That's what allows the air in to bubble. Would it be measureable, dunno?John

author: Ian.M
author_rank: Super Contributor
timestamp: December 29, 2015, 05:23:42 am
content: Why doesn't he simply microwave the potatoes? Personally I prefer them microwave baked with the jackets on, but you can equally well peel them, and put them in a polypropylene food container with a lid and a couple of tablespoonfulls of water if you prefer boiled potatoes.The other option would be a security camera pointing at the cooker + a humidity sensor nearby over the cooker to detect vast clouds of steam.in case he isn't paying attention to the screen.

author: Fungus
author_rank: Super Contributor
timestamp: December 29, 2015, 05:27:10 am
content: Quote from: brossler on December 28, 2015, 08:53:53 pmIn the old days we used steam whistles:Yes, you can get electric ones.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 29, 2015, 11:50:32 am
content: Open loop solution for an open loop problem.Bring a timer.Tim

author: Kalvin
author_rank: Super Contributor
timestamp: December 29, 2015, 12:03:59 pm
content: Or a webcam with a microphone.

author: dan3460
author_rank: Frequent Contributor
timestamp: December 29, 2015, 02:02:17 pm
content: This is just my opinion, as many have pointed out there many ways, easy ways, to get notified when water is boiling, a whistle, a Bluetooth thermometer, a camera, etc. They may be many "practical" solutions to the problem but to me that is not the point of the question posted here. When internal combustion engines got invented was still more "practical" and cheaper to plow a field with a horse, do you see any horses plowing fields today?I doodle on electronics so I not sure, but I can feel that an "electronic" solution can be achieve here. Also my intuition tells me that, because the molecules of water start to move chaotically when boiling, detecting this will be better achieved acoustically. Maybe you will need some kind of hydrophone to pickup the sound and a processor to analyze the sound and emit a alarm or send a text message.

author: Fungus
author_rank: Super Contributor
timestamp: December 29, 2015, 02:09:36 pm
content: Accelerometer to detect the vibration caused by the bubbles?Microphone to detect the volume of the kettle's whistle?Video camera + image processing to see the chaos when the water boils?Ultrasonic distance sensor watching the distance to the surface of the water? (the reading will wobble when it boils)

author: IanB
author_rank: Super Contributor
timestamp: December 29, 2015, 03:16:29 pm
content: I think either you can use a temperature sensor with a mictrocontroller to determine the rate of change of temperature--when the temperature is above 90 Celsius and it stops rising the water can be assumed to be boiling.Or another way is to use the steam. Put a tight fitting lid with a chimney tube, and put the temperature sensor at the end of the tube. When the water boils, a large amount of steam goes up the tube and the temperature rises rapidly. Detect this rapid rise.Unfortunately, using temperature alone is difficult. I have seen this with an automatic tea making machine in Colorado. If you set the temperature threshold to 212 Fahrenheit the machine never switches off. If you set the temperature to 200 degrees the machine switches off before the water boils.

author: Jeroen3
author_rank: Super Contributor
timestamp: December 29, 2015, 03:24:16 pm
content: The typical solution is a mechanical switch, often called clickson, that disconnects when the temperature rises above a certain point.http://nl.rs-online.com/web/p/resettable-thermal-fuses/2047433/

author: Fungus
author_rank: Super Contributor
timestamp: December 29, 2015, 03:34:49 pm
content: Quote from: Jeroen3 on December 29, 2015, 03:24:16 pmProblem: The exact temperature depends on the altitude, the weather, the exact purity of the water ... etc.

author: Jeroen3
author_rank: Super Contributor
timestamp: December 29, 2015, 03:44:12 pm
content: Your average electric kettle does not look at the altitude, air pressure and/or purity. It just heats and stops.

author: Ian.M
author_rank: Super Contributor
timestamp: December 29, 2015, 03:55:40 pm
content: Yes, by condensing the steam on its bimetallic thermostat as IanB noted in post#38. The actual thermostat temperature should be well below below boiling point so it trips quickly when the steam condenses on it. Some experimentation with a vented glass pan lid, a glass bulb thermometer and various shapes and sizes of shroud cut from soda cans should lead to a workable setup. Replace the thermometer with a food-safe temperature sensor once the optimum temperature and sensor position have been determined then switch to an aluminium lid for ease of mounting.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 29, 2015, 04:37:47 pm
content: There have been many good, practical ideas proposed here. Since one of the requirements is to do something new and electronic, how about looking for the steam with a transmission measurement? Using an IRED with a appropriate wavelength there will be a sudden drop in transmission when the water vapor content rises rapidly. Or a similar approach using a humidity sensor. Either approach would require smart processing to first determine the ambient environment and then look for the desired change.Other ideas might be to look for the change in acoustic reflectivity of the water surface as boiling disrupts the smooth surface.

author: Seekonk
author_rank: Super Contributor
timestamp: December 29, 2015, 07:22:16 pm
content: There isn't a good reason to boil. Boiling indicates you are putting more heat into something than it can take. Gt a cheap PID controller and just operate it on P.

author: lgbeno
author_rank: Frequent Contributor
timestamp: December 29, 2015, 08:30:55 pm
content: Wow, so much ink spilled over a simple question.http://www.ebay.com/ulk/itm/262174868572Buy it, stick it in boiling water and see what happens.Sometimes its funny how much things can be over analyzed.Sent from my iPhone using Tapatalk

author: IanB
author_rank: Super Contributor
timestamp: December 29, 2015, 08:47:16 pm
content: And how exactly is that going to tell when the water boils?

author: Seekonk
author_rank: Super Contributor
timestamp: December 29, 2015, 11:27:37 pm
content: Boiling is an indicator that should not be used for cooking. It is used when you have nothing else. The trend in cooking is for precise temperatures. This thread is a totally absurd concept to cooking.

author: miguelvp
author_rank: Super Contributor
timestamp: December 30, 2015, 02:39:06 am
content: why not use an infrared LED? well probably an infrared temperature sensor will do better.MLX90614http://www.digikey.com/catalog/en/partgroup/mlx90614-15/20353?WT.srch=1QuoteEbay has a ton of them for cheaphttp://www.ebay.com/sch/i.html?_nkw=mlx90614

author: miguelvp
author_rank: Super Contributor
timestamp: December 30, 2015, 02:45:58 am
content: Quote from: Seekonk on December 29, 2015, 11:27:37 pmBoiling water is how you could use precise temperature in the past:https://en.wikipedia.org/wiki/Bain-marieEdit: not to count using boiling water to cook spaghetti, or rice.But I think they are not talking about cooking right?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 30, 2015, 03:01:36 am
content: Well, if it's in a kettle, just put a microswitch on the kettle's button.Just for laughs, I measured the resistance of a kettle full of cold water, it started high in the 8M range, then went down to 2M as it heated up and then went back up to 4M as it started boiling.I guess I'd have to run a bunch more tests with control groups, and different kinds of water and probes...Tap water ain't exactly pure or the same city to city.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: December 30, 2015, 03:57:41 am
content: Quote from: Fungus on December 29, 2015, 03:34:49 pmDoesn't matter: the solution as explicitly defined is to remind the cook to know when the water has started boiling so he can put his potatoes in. It can go off a few degrees early and still work fine.Also a lot of solutions here are overlooking the implied problem. A father has asked his son to make him something to let him know when his water is boiling. He can hardly point to a whistle kettle and proudly say "Oh, you mean the alarm that lets me know my water is ready? My son made that for me."

author: Joule Thief
author_rank: Regular Contributor
timestamp: December 30, 2015, 05:24:41 am
content: Maybe its just me, but this might be a way to go. And on sale!I picked one up 35 years ago and the reliability and performance has been noteworthy.But seriously, isn't detecting the water boiling only part of the equation? How do you propose timing when the potatoes are finished cooking?To me, just boil a defined amount of water and time how long that takes (on average), Have dad set an egg timer to come back to the pot after the timer goes off. Surely this will be repeatable to within a minute or so. Put the taters in the water, set the egg timer for 15 minutes and away you go. Its not a proud father bragging rights type of solution, but it does work. I am a father, and as I age, I start to appreciate simplicity more and more - also the undying loyalty and companionship of my "sandwich maker and dishwasher".

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: December 30, 2015, 04:57:38 pm
content: As a small project, I suggest to add a pressure sensor to the device, as for example the BMP180 that can be obtainedon a breakout board for a little bit more than 1$.http://www.ebay.fr/itm/BMP180-Replace-BMP085-Digital-Barometric-Pressure-Sensor-Board-Module-Arduino-KL-/131683793887?hash=item1ea8f73bdf:g:YAUAAOSwSdZWe0njThe temperature of ebullition of water depends essentially on the pressure, with an empirical law (Rankine law)given by T/T_0 = 1/(1- 0.073 Ln(P/P_0))T : temperature of ebullition in KT_0 : temperature of ebullition at reference pressure P_0 ( that is T_0=373.15 K for P_0= 1013.25 mbar)P : Pressure in mbarP_0 : reference pressure (1013.25 mbar).Ln is the natural logarithm.It is thus very easy to :- acquire P, the atmospheric pressure with the BMP 180.- compute the temperature of ebullition of water at this pressure (T) with a microcontroller- acquire the temperature of water through a temperature sensor (DS18B20 for example)- Compare and decide if the water is boiling.I assume that this will give a quite close answer. It will have the advantage of being unusual as atemperature sensor, with the addition of the computation of barometric pressure.

author: lgbeno
author_rank: Frequent Contributor
timestamp: December 30, 2015, 09:52:52 pm
content: Quote from: IanB on December 29, 2015, 08:47:16 pmWell, as others said to determine if there are temperature rise discontinuities when boiling.My point is that solving this problem just like all things, everyone has an opinion but if you want to seek a solution, just start iterating and doing.Sent from my iPhone using Tapatalk

author: tooki
author_rank: Super Contributor
timestamp: December 30, 2015, 11:59:30 pm
content: Well, here's a crazy thought: boiling water is, in essence, a foam. And foams are less dense, and thus less buoyant, than the liquids that make them. (That's why it's easy to drown in the wake of a large ship: the foamy water churned up by the screws doesn't always have a higher density than a human body!)So you could create some kind of device, a float with a density such that it floats on liquid water, butjust barely. Once the water comes to a boil, the steam bubbles cease to be able to support the weight of the float, causing it to sink, which you could either measure mechanically (boooring but probably reliable) or electrically through contact with the bottom of the pan (sparky and dangerous and unreliable but fun!). It would just have to be of a shape that wouldn't catch steam bubbles, maybe some kind of bullet shape.

author: nixxon
author_rank: Frequent Contributor
timestamp: December 31, 2015, 12:15:46 am
content: When is water boiling? What criteria is met when water boils? How do humans sense that water boils? Maybe use sensor(s) that replicate the human senses?What is the optimal water temperature for the task? Does it have to be identical to the boiling temperature?

author: tooki
author_rank: Super Contributor
timestamp: December 31, 2015, 12:55:22 am
content: The OP said it's to boil potatoes. Probably the ideal tool would be a small pressure cooker — you have to load those cold anyway, then you just time it and you're done…

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 01, 2016, 01:32:36 am
content: The most "high gain" (indeed, discontinuous) property of boiling water is cavitation, as I suggested earlier. Make a self-heated sensor that's able to create a steam pocket, but only when the temperature is close enough to boiling that it can form said bubble. Power dissipation falls suddenly as it exceeds the critical heat flux, which drops suddenly around boiling.Such a sensor will also detect sporadic 'boiling' on the approach to a full boil, which isn't very useful (you'd want to average the sensor's output so it only alerts when a full rolling boil is had; just as you would do when watching it by eye), but is at least physically interesting. Only the acoustic method would pick up the same phenomena; temperature and humidity will not.For this reason, I would dare suggest such methods are the closest to: "how do humans sense that water boils?"Tim

author: oldway
author_rank: Super Contributor
timestamp: January 01, 2016, 08:38:21 am
content: To detect the boiling point has no interest since in any case the temperature will decrease when the potatoes are added in boiling water.So it is just needed to detect a temperature lower, but close to the boiling temperature, 90° C for example.In an automated process, the same rule can be applied: from 90° C, reduces the heating power so to reach and maintain the boiling temperature.

author: dannyf
author_rank: Super Contributor
timestamp: January 01, 2016, 12:42:37 pm
content: QuoteA microphone (feeding into a rectifier) probably works.

author: promacjoe
author_rank: Regular Contributor
timestamp: January 01, 2016, 08:44:58 pm
content: first of all you have to understand Some of the dynamics of water that is being heated to a boil. It takes 1 BTU to change 1 pound of water 1°F. It takes 144 BTUs to change the state of 1 pound of water to steam without changing the temperature 1°F. and in spite of what some commercials have said, steam is not hotter than water, although it does contain more energy. this energy is spread out over a wider area, "Approximately 1700 times the volume".As water heats up, it starts to create small bubbles at the very bottom of the pot. As these bubbles rise toward the surface they immediately condense. This causes a A fairly loud high-frequency noise. As the temperature rises this noise will increase somewhat and then start to decrease, the frequency will also change. As the water starts to boil, the noise level will drop dramatically, and the frequency will get much much lower. this difference in noise and frequency can be detected with a microphone. note: Noise from other devices such as microwave ovens, As well as general noise in the kitchen may interfere with this method.To use temperature as an indicator, you would need to detect the barometric pressure/altitude. It would not be appropriate to assume that the customer could or would know their altitude and barometric pressure at any given time. This could easily be done but it would take a bit of experimentation at different altitudes to get it right.The cavitation method, cavitation method may work, but it would depend on the size of the pot of water versus the size of the float being used. Large float in a small pot would Not have the same tendency to sink as it would in a large pot. Also the level of contaminants within the water would also affect this method. an area with hard water, would require a different type of float than one with water that is not considered hard. contaminants from the water would also be deposited on the float. This would make a float heavier and more likely to sink over time.There are several other methods that could be used. But the simplest method is the one that has been used for hundreds of years. Put a whistle on your pot or go get you a pot with the whistle on it.

author: Seekonk
author_rank: Super Contributor
timestamp: January 01, 2016, 10:45:54 pm
content: An interesting mental exercise, but it makes no difference if the potatoes are put in at 207F or boiling. Might as well just use a temperature detector. Nothing else will last in a kitchen.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 01, 2016, 10:55:56 pm
content: Quote from: T3sl4co1l on January 01, 2016, 01:32:36 amWhen the frog jumps out, I know it's ready.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 02, 2016, 01:18:44 am
content: But how do you detect the frog?!

author: dholth
author_rank: Newbie
timestamp: January 02, 2016, 06:56:16 am
content: All of the detachable probe cooking thermometers I've seen are indeed thermistors, available for less than $20, and include a temp alarm. I have never seen a thermocouple style one for sale at the grocery store. Thermistors are very easy to deal with and they tend to use a 2.5mm phono-style jack. Clearly the OP wants to build the deluxe model. n.b. the opening sequence of back to the future, where upon boiling the potatoes are lowered into the hot water with a servo-controlled winch.BBQ controllers are another interesting temperature-of-food application that would make a great project. They use 2 temperature probes, one in the meat, and one to detect the temperature of the smoker (possibly switching power, opening a vent or running a fan to regulate said temperature).

author: oldway
author_rank: Super Contributor
timestamp: January 02, 2016, 10:34:47 am
content: Quote from: T3sl4co1l on January 02, 2016, 01:18:44 amEasy: you know it's boiling when the camera or microphone stop functioning because they have been damaged by the steam, excess moisture or condensation.Why choose a simple solution if there are complicated ones ?...Simply detecting a temperature slightly below the boiling point, 90 ° C for example.It is successfully used on over 120 million Philips Senseo coffee machines.

author: coppice
author_rank: Super Contributor
timestamp: January 02, 2016, 10:51:27 am
content: Quote from: Alex Eisenhut on January 01, 2016, 10:55:56 pmIf the frog jumps out how are you going to finish cooking it?

author: SeanB
author_rank: Super Contributor
timestamp: January 02, 2016, 11:08:33 am
content: Quote from: coppice on January 02, 2016, 10:51:27 amPut the lid on, when the thumping stops it is ready.

author: Ian.M
author_rank: Super Contributor
timestamp: January 02, 2016, 11:17:47 am
content: More to the point: How do you persuade Dear Dad to use some fancy boiling pot detector gadget when he's already too absent-minded to reliably check the stove X minutes later?Older adults do tend to become set in their ways, even if they still retail all their mental acuity, so I predict that unless Dad has requested such a gadget without any prompting, if it requires any user intervention to activate, (even if that's putting the right lid + sensor on the pot) its likely to be ineffective in practice, even if the solution is technically brilliant

author: Joule Thief
author_rank: Regular Contributor
timestamp: January 02, 2016, 04:03:42 pm
content: Buy a tabletop induction cooker. By the time dad slices and dices, the water is boiling.

author: bson
author_rank: Unknown
timestamp: January 02, 2016, 05:27:11 pm
content: Interesting problem. As an engineer I've already measured the time it takes to boil 1, 1.5, and 2 quarts of water in a particular pot on the burner I normally use. (And makes up for water volume variance due to the eyeball measurement method.) I set the timer to about 30 seconds short of the boil time, which gives me time to reset the timer, verify boiling is imminent, then go fetch whatever goes into the water. When the rolling boil starts I lower it in. (Usually it's eggs. And yeah, I've measured the perfect amount of water, boil time and thermal curve, and icing procedure for 12 perfectly boiled eggs without flat tops. We use gas here so burners adjust immediately; clearly electric burners would need a different adjustment curve due to thermal reactive lag.)Calibrate, people. Calibrate!But on a more serious note, boil detection is an interesting problem. I'd consider a piezo element attached to the pot (outside) and sample boiling sounds from a variety of fluids. Use it to create somewhat fuzzy correlation kernels, or maybe a single kernel if it's possible.