 This week's IonMPI is from Kemet. Lady Aida, what is your pick from did you key this week for IonMPI? I'm glad you asked. We got this. This is a series of sensors from Kemet. They are the TRS series of thermostat sensors and what's neat is I actually learned a lot writing this IonMPI because I didn't I misunderstood how they worked. I'm going to explain to you how these sensors work. So these are sensors that basically they're in like every appliance you know and essentially they're a switch that when you hit a certain temperature they either open or close. So let's say you have a heater blanket or something. Obviously you don't want to get it so hot that it could burn you. So there's a thermostat but maybe there's also a safety interlock you know if the heater blanket gets too hot the connection opens your heater blanket no longer gets electronics electricity through it and it turns off. You know likewise you could have an alarm in your freezer the temperature goes below or above a certain point it's you know either gets too cold or too hot and alarm goes off and you're notified and that could be done with this very simple switch no firmware coding required. So there's the thermal read switch series so it comes in a couple different packages and we'll show you this and there's multiple different ranges so each one has a set point that either make or break below or above that point. So the make ones you know when they go above the temperature they make the connection the break ones when they go above the temperature they break them whichever make above make above break break and they come in different sizes and shapes with wires or not or you can solder them onto things. I got a couple that were solderable and this is interesting so you know I was actually I thought that these kind of worked like PTC fuses which we had talked about a few you know weeks or months ago we covered a couple PTC fuses where the material as it gets hotter the resistance changes but actually these use the curie point like the scientific the theory of the curie point which I remember from like high school and college so this is a really neat thing basically we have some magnetic materials and you know you have all the spins going in one direction and that's what makes you know there'd be a north and a south pole to the material but then you know sometimes you know sometimes you hit a material it'll scatter the crystal or if you get it above a certain temperature and what's interesting is it resets like if you you heat it up to a certain temperature and then the crystal kind of breaks apart you no longer have this magnetic property it doesn't act like a magnet and then when you go back down it reforms into the crystalline shape and the magnet the magnetic property reappears so what these sensors do is they have a special material that the thermo thermo right which is tuned by Kemet to have that effect the curie point at like 15 degrees C intervals so it's like 40 55 65 75 whatever and you can see in the graph they have in the different points and they take a really hard stop like when it hits that point it really does like turn from a magnet to a non-magnetic property almost instantly so inside all of these sensors is basically a reed switch which a lot of folks here have probably used before this is a generic reed switch that did your key stocks and the reed switch has two metal plates and usually and there's they're in a glass case or you know some other case that's totally got in inert gases there's nothing inside there's no oxidation that you have to worry about and when a magnet comes close the magnet causes the two pieces of metal to touch to make the connection or separate to release the connection and so we've used these for like door and window sensors you know when when the magnet comes close it closes the connection an alarm goes off or vice versa but with a little bit of clever hacking you can turn these into temperature sensors so this is basically how like a reed switch works normally in the top right there you've got a you know a magnet and it comes close and the two pieces of metal touch each other and there's a a magnetic field on the left side I mean this diagram is from the data sheet this is good but I actually like let's get we'll skip ahead because I'll show the very nice diagrams so there's two types and basically they do like a thing where the outer ring is that thermo right that material should get is a magnet until the the temperature rises a certain point and then becomes demagnetized and for the brake type the the thermo right's in the middle and there's permanent on the outside and on the make type the thermo right's in the center and then there's a little bit of a spacer and I'll show you the video also because it's kind of interesting how this hack but in the center is a normal reed switch okay so for the brake type I thought this was we know both they're both kind of simple to well simple but they're easy to understand so there's the reed switch on the inside and see there's on the center there's the pink thing which is which is a cutaway of the ring and at the low temperature the middle part is magnetic and so the two permanent magnets on each side there's a continuous field that's not broken and so it the reed switch is closed and then when it gets very hot that center part again becomes a magnetic the pink part basically acts like a open connection and there's no transference of the magnetic field through the material anymore the magnets no longer right next to the magnetic field is no longer right next to the the two reed switch leaves and they open up and now the switch is off and then when the temperature goes back goes back down it remagnetizes the field flows again and vice versa so like no power is required no sensing no code it just magically happens at the curie point um likewise the make type uh is sort of similar except there's you know there's two thermo right rings in the middle and the magnet and basically the same thing where it's like you want to create or remove the magnetic field which would connect or disconnect um the reed whichever whichever way you want I mean usually people have a brake switch because your toaster oven it gets too hot you want the electronic the electricity to disconnect and these come in multiple different shapes there's also the ohd family which is like sealed and comes in like this epoxied enclosure and that's uh for u l csa or tv rating um there's you are waiting for looks like one of the lead terminal ones but these you know you can use for anything again they're very simple they just kind of work um physics seems to have not let us down yet uh so far and so you can rely you know you can rely on this knowing that there's not going to be any like funky weird you know watchdog timer that has to go off or like oh what if you know the the ptc thermistor isn't like you know it has some leakage current like this opens a reed switch it's open it's open like it's there's no electricity passing through um there's just some things that you know they they show what they're they're used for you know refrigerators and rice cookers and uh water and whatever you know there's there's basically two use cases I think of that are really good one is as your main control like I mean these these could work as a great sensor input into a more advanced microcontroller um you know definitely you don't have to you can just have a switch and it would uh activate an interrupt or or what have you just you just know whether it's above or below the temperature but it's also great as an interlock you know you have a more complicated feedback system but then like if that feedback system fails for some reason you have something like that protector element it's like no matter what it will never get above this temperature because if it did uh the electrical the electrical connection would open and if you're not sure which one you want there's also a kit that uh did you keep it together with kemet that has like kind of one of each make and break and various temperature uh trip points the curie points uh so you can pick up this kit if you just like want one of each if you don't know whether you want make or break type or what the temperature rating is um and these are the parts that are in that kit so you get like you know from 50 degrees up to 120 degrees half make half break all of them can pass um 100 volt ac and uh looks like about 0.3 amps um so good for a signal or even low power available did you key and because we're showing this it means it's in stock it is in stock um i got a couple of them but there's um there's like every rating is available you know it's like i actually really like stuff like this because i feel like you know i spend so much of my time in like firmware and like firmware is great but like i would never trust it with my life um with my safety whereas i would trust something like this it's like it's the curie point it's physics like it's reliable i i believe in physics yeah all right and we have a little bit of a video that has some of uh information about they haven't very nice it's much longer but we have a little snippet yeah let's shift our focus to the operation principle of the thermo sensor simply put it is a thermal switch that opens and closes the contacts within its built-in read switch by the shift in magnetic energy of thermo right and permanent magnet here a ring shaped thermo right is in the sensor sandwiched by two ring shaped permanent magnets with polarity arrangement as shown with a read switch fixed inside the rings when the temperature of the thermal right is at or below its curie temperature it functions as a magnetic body in contrast when the temperature exceeds the curie temperature it becomes a non-magnetic body this change in the characteristics shifts the magnetic circuit which makes or breaks the contact in the read switch the thermal sensor has two types of switching action break type and make type the break types mode is normally on that is turned off at the operating temperature as opposed to make type which has a mode that shifts from off to on