Ah, a glass of chilled white wine and the Electronic Module out of a toilet fan. Life is good. This toilet fan instead. they came from me B and it came from a Uk-ish supplier.

see: Yukio doesn't seem to it doesn't have a professional floor to it. Here is the manual, which is kind of like shredded diagonally uh, which excludes some information and doesn't necessarily relate totally to this uh, this unit nor the information. It's a bit odd. Anyway, let's take a look at it.

So the fan I should explain. In the UK are bathrooms. their room with the toilet and the shower and the bath in it typically has a wall fan that is either four inch Plex inch. it could be any size and there's a little Electronic Module in it.

and when you turn the light switch on, the fan starts as well. and uh, when you've finished having your your business, if you've gone in for a quick pee or whatever, some of these I think this might do this I have a time delay that as soon as you turn the light off, the fan goes straight off again. but if you've been in for a longer time like having a poo or having a shower or a bath, it will run on for a time that has been determined by the time setting. the potentiometer that could go in this unit from about 15 seconds up to 45 minutes I think which divides nicely into a binary multiple, which we'll look at later in the actual schematic.

and the idea is that by continuing to run after you've left, it just takes the remnants of the humidity or smell out of what you've done. I Shall put that out the way because we're interested in this little module here. So on the module now Zoom down this and it's unusual that this one has a humidity sensor as well. There's a track that controls the motor and the fan.

Here's the humidity sensor. This sets the humidity threshold and this sets the time. I Think the idea of that is it will run for a certain time, but if the humidity is above a certain level as detected by this it and the setting here, it will just keep running until the humidity is reduced to a sensible level. Let's take a look at the circuit board, which I conveniently have right here in a blue and out proportion type size.

Note that the text is backed front simply because I flipped these images just to make them match what was in the back of the circuit board. It just made it easier to reverse engineer. So there's the supply cables coming in. There is the triac which is a little tier 92 type package.

a Bt131. Uh, we have a metal oxide varista which clamps any voltage spikes. We have a one key resistor, a brown black, red, one zero and two zeros. Uh, to give one thousand ohms and that is actually before this metallox.

Everest I'll show you that in the schematic and it's part of the power supply. Here's another part of the power supply: the smoothing capacitor. There are the two potentiometers both 500k and there is the humidity sensor. Now, the humidity sensor in its own rate is very, very interesting.

On the back circuit board, we have a 100 nanofarad fair to high voltage rated capacitor which forms part of the power supply soccer tray. And then we've got this very tight bit of circuitry here. Uh, two little sort 23 packages as inner diode and a dual diode package which is quite a. This is a really tight circuitry, quite neat.

And then the electrolytic. We have a identifiable microcontroller which makes a change. We have the transistor. the transistor is a special function here, and we have the humidity sensor on the other side.

Oh, and also see these two 205, 20 and Five Zeros. So two million Mega to Megan Um, not 2 million Mega 2 million Ohms two Mega We've got two of them in series for four. Mega They detect the switch input from the light switch and also it oddly, it detects the live as well. I Think it might be using it as a timing reference.

Let's take a look at the schematic. Foreign. So the schematic is divided in two sections for ease of uh digesting its technical knowledge. Here's the Live: A neutral communion I've drawn the neutral at top for a very specific reason because it is also the plus 5 volt.

Rail and the zero volt rail is negative to that. So effectively, the triac, which is reference to neutral is being pulled with its gate. it's being pulled negative. Now a track is a a little specialist component that is designed to switch alternating current.

It can switch in both directions, but you can also trigger it in all directions. If well, this ends positive or negative and this ends. Uh, the triac. You can the Gate of it.

Wow. let's try that again. Too much. Wayne Perhaps where this end is positive or negative, it doesn't matter.

or the gate is positive or negative. It doesn't matter, it will trigger it. but it's most sensitive when pulled. negative to the uh, what they call Mt2.

this is Mt1. This is M T, two main Terminal one, main Terminal 2 and the gate. Useful little components. Also worth mentioning that once you've triggered them, the latch on this stay on uh, solidly until the means same wave crosses through the zero.

Crossing Point The current drops to zero and these will reset and then it just gets driven Again by the microcontroller. There are the two Uh Two Magnum resistors in series for both the switch switch live from the light switch and also the general live. I Think it. The only reason I can think for this is It's using it as a nice 50 or 60 Hertz timing reference.

So the Live comes in and it's limited by this resistor. It's a very low current circuit, so it's using a capacitive dropper. but because it's quite a low value 100 nanofarad here of the capacitor. um, it's uh, it can have a big high value resistor that is multiple advantages.

It reduces the inrush current if there's spikes and glitches, if you turn the Circ the power on at the peak of the sine wave, or if there's if there's a lot of electrical noise. Capacitive droppers will generally pass that noise because the capacitor will just basically get through. uh, glitches and high frequency noise. So this is where the one key resistor comes in handy.

I Suppose that also acts as a fuse number the fact that the 470 volt metal oxide varistor. Now depending on how you want to draw it, you might want to draw it like that or that that isn't actually having a very hard life because when it clamps any voltage space which is purely protected electronic circuitry, this 1K resistor is actually doing most of the work there. So there's the 100 nanofired capacitor, but because it's being referenced to one of the supply rails, it has a very simple system that if it's a negative, current flows from the zero volt through this diode, but if it's positive, it just bypasses it straight to the neutral. It means it's very.

It's almost inefficient, but it's not need. It doesn't need to be efficient in this case because it's very. low current. It's not as efficient as having the full Bridge rectifier, but with the two diodes, it's a basically creates a a five volt Reel with reference direct reference to one of the supply, the AC Supply rails.

That's pretty hard to describe actually. Now these two diodes have arrows pointing at them from P. Y. That is sweet.

It's a little dual diode package. Um, and it just means it's a tiny little sock 23 package that's A that's it there. and just the way they've done it is just. it's kind of cute.

Really quite like that. Likewise, the Zener doubt is a Z2 It's also sort 23. 5.1 volt doesn't have to be big, not dissipating a lot of heat. This whole circuit runs at very low current.

The most current is needed by the triac, which takes about three milliamps to drive, so it's well rated for that. So this inner diode clamps it to 5.1 volt, the 220 Microfire capacitor Smooths that. and then there's a coupling capacitor mainly for the microcontroller, and that is that the Py instantly. the Dual diode is a Bav 23se.

quite interesting package. um, and the final motor being switched to the track. That's the full power supply covered. Let's go on to the actual, the exciting bit.

the electronics. The microcontroller because that's what they've used. So the microcontroller has one output. well, one output for functional properties and that is to the track.

and it's got one key resistor, five volt, Supply one key resistor. Also, the Uh gate drop of the track, which you see about one volt 0.6 to 1 volt means that this one key resistor is going to easily pass the three milliamps required to drive that track. The two inputs the from those Uh resistors, these little resistor dividers. Here, these both these resistor current limiters, the two two Meg Ohm resistors in series or four Mega they go straight to the microcontroller.

That's a common thing. Uh, it doesn't matter the fact. it's quite a high voltage because the inputs of the microcontrollers have a diode to the positive Rail and the diode to the negative real that basically stops uh, the supply rail being exceeded by a excess voltage. And it's a common technique for detecting.

In the case of the Ac1, it's detecting the zero crossing point. and as I say I think that's either for Uh timing purposes or it might be so the track is only fired at the zero crossing point to reduce the current Spike through the track. perhaps because it's there's at the zero Cross Point There's zero Uh current flowing through the track and the switch input was just purely monitoring that light switch is worth mentioning that for safety, uh, these ball fans have a isolator next to them that breaks not just the live, but also the switched feed as well. Sometimes I I'm not really up to date with that.

Does it break the neutral as well? I Think it probably does because they're all super safe these days. The microcontroller also has a little capacitor because it's got an internal reference V Cap it's called 1.8 Volt. It provides its own 1.8 volt reference that's probably for uh, analog to digital converters and it's using them on this. So it's got one output here and then one input.

The input is from the humidity sensor, but the output is doing double duty. It's acting both as an input and an output. Now here is the time setting potentiometer and it simply goes between 0 volts and the 5 volts. So this, uh, plus five is actually tied up to that reel and it's got a 200k resistor for a good reason.

So I'm guessing that maybe it only looks at this when it's powered up, but it might not be. but uh, either way, it reads that potentiometer just as an input. by looking at Analog voltage. it's going to either be 5 volts or it's going to be zero volts and that's going to give it the software queue for the time delay it's just going to use our it's going to convert that to digital zero to 255 level roughly, which will determine uh, the time delayed incorporates for you turning off the switch and how long the fan runs, but that input is also an output and the output when it's triggered, has a capacitor isolating it from a transistor.

And the reason for this is because the sensor the humidity sensor looks like this. Inside it's a ceramic substrate with conductive carbon ink, electrodes, little fingers interleaving, and then what you can't see here is it printed over the top of that is a polymer that is hygroscopic. It absorbs moisture and depending on the humidity, it will have a specific resistance resistance that relates to that humidity. and you cannot use these as resistors as such because if you've seen these modules on eBay and they are available on eBay right now, don't buy these modules.

You get two versions. You get the version of the relay, You get a version that just puts analog and digital output to your Arduino and it uses these sensors. Wrongly, They it's going to destroy these sensors. These modules just won't work in the long term because it's using that resistor, that variable resistor in conjunction with this potentiometer, and it's sensing that uh, the voltage divider voltage depending humidity with an LM uh, probably LM of the generic or pump 358.

I'm guessing that's a three five eight. that's kind of fits, but that's the wrong way to use these. You can't use these like that because if you use them as a voltage divider and you're passing DC across it, it causes Uh electrolysis effects. It causes migration and material from the electrodes into the Uh, the conductive gel on the surface and it.

damages. It changes its Uh State and it makes it drift quite significantly over time. So to avoid that, you actually have to use these with a capacitoring series basically and you have to pump them and then get your voltage measurement uh by causing say this end going positive and then it goes drawn diagonally positive and then negative. which means current flows from One Direction and then it flows through the other and that counteracts Itself by providing EC current flow through these.

So the way it's doing this is: this transistor has a pull down resistor. it's all low current 200k cooldown resistor and a transistor pulling up to the positive reel. And when the microcontroller pulses that output, this capacitor ensures that there's just a post fed to the transistor, it can't pull it on continually. and that also that capacitor also decouples these resistors so that it can actually monitor this input.

It's quite complex. They've cheated in a very clever way. I Mean the person who designed the circuitry was on the ball. They they knew their stuff and so that capacitor lets them treat that as an input and the output because this transistor will need to be pulsed.

When the transistor is pulsed on, it pulls the input to the capacitor positive and then when it turns off, it goes negative. Again, that's your EC It's providing that sort of positive transition and negative transition so that this humidity sensor here can only see current flow in One Direction of a certain amount and then the current flow back in the same amount so it doesn't damage it. It doesn't cause that electrolysis effect that then forms a potential divider with this 39K resistor. Now the reason there's a question mark next to this is because I had a bit of an incident.

The resistor was either upside down or unmarked or something. So I measured it in circuit 1.39k I Then thought I should take that out of circuit and measure it and I took out of circuit and then it was a bit floppy and there's a Big Blob of someone in. So I grabbed it in the tweezers and thought as I was doing I thought I better not ping this and then it pinged and it's gone. It's that resistor is toasted.

It's somewhere in this room I don't know where it is. Anyway, once removed, that was quite High impedance. So I'm guessing it was a 39K resistor. Probably it's gone.

Can't prove that. Likewise, these capacitors in circuit are measured 4.5 nanofired. Closest to that's 4.7 nanofard. 800 nanofr.

Closest to that is probably about one microfarad. Um, to tune the value of that humidity sensor, they've got a 620 key resistor in parallel with it. and then the tap of this potential divider is going through a potentiometer and then a resistor. and that again is to tune it.

Probably in this case to tune it. up in the upper level of its range so it's only looking at humidities between about say 60 to 90 percent. These resistors are all chosen, uh, the parallel one and then this one and the arrangement of these resistors is chosen just to tune it. So the full span of that uh, potentiometer, that variable resistor just covers the range they wanted it Tunes in and then output of that as a measured as a slight voltage goes to the input of the microcontroller.

and therefore when it toggles that output, it pulses it. It can actually look at the input and it can see what the humidity is in the room. It's very clever. Maybe I should have drunk so much wine before making this video, but you know what? It made it so much easier and more fun in the process, but that is it.

It's an interesting little circuit board I could replace that with a 39K resistor and it may work again, but it doesn't really matter because the only reason I bought it was to take the thing apart so we could take a look at the circuit board inside it and we could reverse engineer and see how they'd actually measure the humidity. And uh, it's worth mentioning that you do get other humidity sensors for the Arduino type modules that are not the little two pin ones. They are three pin ones. The three pin ones are fine.

Uh, Dht11 Is it Dt11? Not sure. There's a couple of different models, but they have three pins and uh, it's basically 5 volts, zero volts and data. And those things have all the circuitry built into them. and uh, they will provide temperature and humidity as a data stream back, but that is it.

Very interesting circuitry, well worth exploring. Um, and it was worth getting just to do that just to see how they've done that with that cheap humidity sensor. Very, very interesting.