Please excuse the temporary change of environment, i'm not back at my normal bench yet, but i will be back at the bench in the future. Well, here i've been digging out other stuff and found this old ozone generator. Now this ozone generator had two functions. It was either designed just as a room or space ozone generator or you could clip a little housing in the front.

There are two pipes: two flexible pipes that you put into footwear and then it has a 12 volt supply and you can either choose a single pulse single shot mode where it will just run for a certain length of time or you can choose continuous running uh. Just for as long as you want then turn off, but when you turn it off well, first of all, this overrides that so i'll unplug this and see. If i can reset that plug it back in no, it's not reset it. Right too, i shall have another go it's a quirky thing, because it's not based on microcontrollers.

If you turn this off, it doesn't just shut off straight away. It does this thing that it ramps down. Slowly, can you hear that the fan is slowly ramping down and then it shuts off? Okay, let's pop the lid and explore it. So inside is uh us now.

I've just hit the button inside is an air guide. It's got a standard computer style fan at the back, and then it's got the ozone generator with its high voltage supply down. Here they have scrubbed the number off the chip which i'm going to guess and we'll deduce this we'll take a look at it. I'm going to guess that's a 555 that they've done that too.

I'm not sure why they've gone to such secret degrees, but anyway we should explore it. The ozone tube is a dielectric barrier tube. It's a glass tube with a conductive coating inside and then a bit of mesh outside and because it applies high voltage ac across it and because it can't arc through the glass. As such, you get capacitive coupling and where that capacitive coupling occurs onto the mesh and outside it creates a slight purple discharge, and that is the ozone uh.

What generates the ozone, the corona discharge, and then the fan blows the air across that? Let's unplug this underneath this is the control circuit board. Oh, i can unplug that i shall unplug that and the control circuit board has let's say, unplug everything and get my little magnifying glass in ka555. So it's using a 555 again, i'm going to guess that might be part of the automatic shutoff circuitry. When you push the button, it probably triggers uh, it charges the capacitor and then the capacitor slowly discharges until it cuts off lots of transistors uh.

I don't really have the facilities here to start reverse engineering, this i'm just going to be exploring and, to be honest, the circuit board i'm most interested in. Is this one, the one they're being all secretive about? We don't like it when they keep secrets from us. Let's take some screws out here, so there's four screws in the vicinity of the ozone generator tube. This is kind of old hat.

These days i used to use everything out of desperation. I had stinky feet. My work boots used to really stink like really offensively stink and the cure it turned out was boric acid, fine, powdered, boric, acid or or not fine, parabolic acid, that you've sprinkled into a um put into a coffee, grinder or something and turned into fine powder. So why do we have there's a transistor right next to the high voltage transformer? I don't think i'm going to get a zap off of this actual.

I shall finger everything and get any shocks over with no that's fine. We've got the ozone generator thing, which uh has one connection go up to them. This is very messy, underneath very messy, but they've got the this loop of wire that holds up also connects onto the outer mesh here, and this central connection is going inside and the glass is cracked here. It doesn't really matter, although it could technically speaking arc through or is that just resin? I'm not sure.

I think the glass is cracked, it doesn't really matter, but that has the conductive coating they've put a conductive paint inside to provide a continuous conductive layer. Inside of that tube, this is the fairly standard high voltage transformer with the core and the winding in the middle. It looks as though it's only going to be two connections, because the transistor here is actually doing the switching of that, and i would guess that transistor is being switched from. Pin 3 of this chip, which is going across here and through a resistor and through the transistor, that is exactly what it is.

This is just a five five five, the one number if the chip that they've scrubbed the number of how strange that they've gone so secretive and they've got a facility to fine-tune the oscillator to match the transformer and that's what ultimately generates the high voltage interesting stuff. Let's take a look at the other components in here. This is quite a complex little circuit board. It's also held in with an excessive number of screws.

Far too many screws. I think they were trying to be serious here. I shall also pull off the power connector and i'll see if there's any clues in the bottom of this, but it's a single-sided board, it's quite densely packed. It's got one two, three, four, five, six, seven transistor like things and the five five five and one of those transistors will be switching the uh.

Well, the transistors may be being used as latches. Are they sure it's a very densely packed little circuit board? That would take a bit of tracing through and it's the sort of thing that not only would it take a while to trace through, but i'd have to um i'd have to uh, basically take a photo of both sides to actually facilitate tracing that uh. I'm not that keen on doing that, though, because it's kind of old-fashioned. I know it's nice that you know it's not microcontroller based but um.

It is just uh paying that reverse engineering that quite frankly, and it's just a crappy old item anyway, it's kind of out of date, these days, we'd use a different approach for generating the ozone, uh and so low levels or we'd use the little ceramic plates which Use the same technology, but not this of clunky old, tube based system. This is just two resistors uh, three leds and two switches, one of which is latching and the other, the momentary one for the triggering the the controlled cycle. Uh just doing a single press, it's non-latching, the fan is rated. It says dc 350 milliamps, which is quite powerful.

Actually, but that's it that's. What's inside this, it's very retro, it's uh kind of does its job. I suppose i kind of used it for a bit, but i didn't really use it an awful lot. It wasn't that great uh, but certainly it's probably more fun, just taking it to bits than any of the uh use of it bonus extra footage.

I have reversed the high voltage section and uh the reason it was looking so terrible in the back is that past big clive has obviously had a go at this because things have been marked and coils have been drawn on. So i have reversed this engine. It reverse engineered this in the past, but nonetheless i have reverse engineered. It again found something quite funny, so it is based on uh i'll, just speed all the dust off here.

It is based on a 555, the they've gone to great lengths to paint over all the numbers on the capacitors and resistors, and also scrub the top off the chip, because this is their super secret circuitry. It's not that secret. The 12 volts comes on here's the common zero volt rail 12 volts comes on decoupling, capacitor and smoothing capacitor, and then there's a little uh inductor for reducing the passage of electrical noise and then another um, smoothing capacitor, and it's worth mentioning that the same circuitry is On here, the main control circuit board has the power coming on. It goes through a polarity protection, diode, uh electrolytic and the covering plaster, then the little inductor and then more electrolysis.

You can decoupling they've gone to great lengths to keep the power uh clean um. This 555 is directly controlled from the switch by the way when you trigger this one. It is introducing a single step delay, but the rest of it is just the transistors are for switching the loads or level shifting or buffering as darlington's. It's actually very, very straightforward, but that's not the bit we're looking at we're.

Looking at the high voltage section, which is based around the 555 classic, i believe it's the a stable configuration is that right, i think it is, and they've got the usual resistive divider here. One of them is a variable resistor, so they can trim the the output speed of the 555, the frequency to match the inductive load. The transformer things worthy of note, the pin five - should normally be coupled to the zero volt rail, with the capacitor just to provide internal stability, they've not done that they probably just didn't think it was needed. I don't know what value this capacitor here is.

I've just said nanofarad because that's what it's going to be probably, but this then puts out a roughly square ish wave. The mark space ratio would depend on this setting here through a 680 ohm resistor to a mosfet. The mosfet is an irf234n really common mosfet and its switch is the primary of this transformer that has a little capacitor across it, presumably as a tuned circuit, also potentially to clamp any sort of spikes when this turns off. Although there is inherently the diode built into the mosfet flap that then steps the voltage up to the secondary, which is reference, the zero vote rail and has the dielectric barrier uh across it, which jet then generates the corona discharge in here that the air blows past And that creates the ozone, and it is quite funny that uh i saw that cracked glass and it didn't twig at the time, but the mesh around the outside they've actually seen them.

It must have maybe arced in the factory through that crack or they saw it. They've taken a red, sharpie and they've marked the mesh round and they've cut the mesh clear of the crack, so it does work. I don't think it would have been me or did that. I think it was probably them um, but there we go.

That is it. So that's the bonus extra you get the high voltage circuitry, the rest of it is just fairly textbook, either straight on off um odd, that they've separated the fan and the ozone generator. So the fan runs on a little bit. It might just be a little gimmick to actually purge air through to make sure there's no ozone left in the unit.

I don't think so, but the rest of it is just basically level shifting and stuff like that. It's not that complex, but that is it. The circuitry of the ozone generator for sterilizing footwear as reverse engineered.