Let's take a look at this banned voltage detector. This is one of these things that when you hold it up to a live connection, it lights up at the tip and you think, well, hold on. they're not banned, you can still get them. Well, that particular one of this is very flickered.

See, that's one of the problems with the safe. Replacements is they're not that safe? Oh, that is not a good one. But anyway, the reason that this particular tape has been banned is because the first ones of these had metal bodies and it meant you got a really good battery connection. But it also meant that when you were poking around in electrical panels holding the end of the metal tool, the rest of it, the metal body was potentially going to touch Live contacts in that panel if you're careless and give you a shock.

and that's why the Bandit However, let's open up and take a look at what's inside. I should tip out the batteries. This is ancient. This is really old and I've probably had a part.

It's supposed to have a little Pip across the end like that, but this has been destroyed in the toolbox. Is this going to come off? I Don't think it's going to come off too easily. Let's grab it with pliers and try and get it off this way. Oh, that does not want to come out.

that is not want to come out at all I may have to pause. well. I Try and extract this from here that is super strong I'll look inside I Don't want to damage the circuit board because I want to reverse engineer the circuit board for our entertainment. Hold on.

Oh there it is. there is. So for reliability, it's got a wire folded well. I'll show you I'll take picture of this so you can see up close.

Yeah, that's what I'll do but the connection into the body. This metal body is literally a wire folded up the side and connected on. and that's the uh, well, it's one connection. Is it a positive end? and well, no, the post event is coming down here.

that must be in the negative end up the other end. Oh, that's gonna hurt. Let's grab it with the Polaris again very carefully and with there's half a circuit board. that's not a good start.

That's a very bad start. It did not like that at all. I Feel like I've oh, a ceramic, right? Okay, tell you what at one moment please. I'll just take a picture and we'll take a much closer look at this.

It turns out that cracking that ceramic circuit board might have been a good thing because I just went right to town on it to call the surface mount components off. Um and uh, found that there were hidden printed resistors underneath the integrated circuit and here I've cracked the ceramic. I Think the designer also used a sledgehammer to crack a knot here. It's a very complex design.

Let me Zoom down a little bit closer so you can see this. So this is the circuit board cracked before I take the components off it. this is afterwards. this component here the cryptically named 8c14 is most likely a 74 Hc14 which is a CMOS version of a TTL chip.

Um, there's a dual diode package which I took it off and thought is that a dual diode and I just stuck it in the component test with component test to identified it incorrectly as a transistor and gave a gain value I'm not sure how that worked. this however, is a transistor. Um, there's a couple of capacitors filter capacitor cross Supply um. timing capacitor and filter capacitor for detecting the AC Mains right? Tell you what.

let's go straight to the circuit board. Oh, this is the only resistor I Couldn't measure in circuit because I all these other printed carbon resistors I was able to find adjacent pads and get a resistance Freedom they're all very high value this one because of it cracked I Couldn't get a solid reading in that but I know from its position in the circuit I'm going to guess something like 100 Meg Ohm, it's going to be super high. Let's take a look at their schematic. anything else to look at here.

Nothing really okay. Very expensive circuit board to make. strange I'll show you the other one afterwards, which is not an expensive circuit board to make. Incidentally, this is the dodgy one that's pushed band because the metal have reincarnated it with the Uh with the circuit, you can see it flashing there.

It doesn't. Flash In real life, you're seeing the 50 hertz pulsing because I've put the other circuit in it. Anyway, we have rather, oddly, a 10K resistor I'll mark that in 10k being used as an antenna here. So initially we've got the three volt Supply From the AAA cells.

we've got a one Nano fired capacitor process. That's not a very high value, but the whole current of the circuit is tiniest. so it's an ample for the filtering. And we've got that little chip which contains one, two, three, four, five, six, uh inverter Gates And those inverters are Schmidt trigger inverters.

Which means that as the voltage into them Rises the output will suddenly click on and then as the voltage falls again, it will suddenly click off. There's a sort of hysteresis and a very decisive on off switching. This is useful. They're incredibly useful components.

so the resistor here is just basically to cut the lead off. and it's used basically to fill the tip of this probe with conductive material in the form of the resistor. I Suppose it was the cheapest way of doing it and it's self-centered in the probe and give us a large area for the pickup. There is this massively high value pull down resistor to allow the Street pickup field from the tip of the probe to actually influence the input.

this Geeks there if it was just left floating, it may be too sensitive. This has been used to tune it down and actually give it a certain thresh or before it will detect. Once it detects the AC coupled signal from a live wire, it goes via this 10 mega Ohm resistor and to the input of the gate. These gates are super sensitive and then the output of that gate will start pulsing up and down in time with the sort of mains alternating current that is then filtered via this capacitor.

So only pulses will affect the output which is unnecessary. And and there's a 10 nano farad at 10 nano 10 mega Ohm resistor pulling the input to this logic Gate High to keep it in a stable state. That then effectively because this one's pulsing via capacitor, this output starts pulsing sharp spikes. Um, the output then goes through what's called a charge pump.

This diode here only lets the current flow in One Direction and because the output of this is effectively pulsing high, that Uh uses those pulses via the diode to start charging up this capacitor and after a certain time delay determine this resistor. The input to that gate will go to a level that changes state. So this is used just to introduce our time delay to stop spurious glitching and this discharge resistor here just makes sure that once the pulse have stopped, it brings that down again and it basically goes back to its standby. State waiting for more pulses.

The output of that then goes to this gate which then because it's inverted, goes through another inverting gate to then drive the transistor which then switches the LED on Via What was that? resistor? 21 Ohm at 21 Ohm resistor. So let's uh, recap very quickly. the input of this gate is being pulled Low by this resistor. so the output is high, but nothing happens because of this capacity to block the signal.

When that starts, Um detects the signal. it starts pulsing the output opposite part in then current can flow through a capacitor this is normally being pulled High Which means the output is normally low which means no current flows through that diode. When this starts pulsing that, then positive pulses then go through this diode and charge up the capacitor. The capacitor is normally the input to this key is normally pure low which means the output would be high and when this starts pulsing it reaches that threshold that then goes low which then gets verted again goes High Turns on the transistor, switches it Led they could these Gates Can they can sink a bit of current? Not a lot of current, but it would have been enough theoretically to drive the LED They could also use those spear Gates Theoretically, you can give your opinions on this.

In a cluster like this, this is just a thought to actually beef up a little bit. Well, that's just drawn. that was a diode that's not a diode. um, and maybe get rid of the transistor.

But anyway. the other circuit that we got the other probe is a lot simpler because this is just ridiculously complicated. The other circuit has three transistors. One set is a high gain input that's this one and then the other two is a Darlington switching.

The LED um and I'll show you the schematic for that. I mean that's basically one resistor and three cheap transistors. The schematic occurs much simpler, much much simpler. This is the one you'd want to build for fun.

It doesn't really matter, it's fine or light when you put it in your Live Wire We've got the Tripoli cells to them. given the three volt. Supply The in the base input is literally a spring to give it a wider electrode with a stiff wire up the middle of it. They're just looking for a fairly large sort of basically uh, well, they've basically a spiral like that just inside the probe tip just to give it a sort of largest detection area.

It increases the effect of the capacitive coupling. so it goes to the input of this C3199 transistor and uh, that has a three Meg Ohm resistor pulling the base of this Darlington Pier down to the zero volt reel to keep it off. Quite a high value because this has to override it that buffers the detected signal up. It effectively pulls that high turns on the Darlington and the LED is in Sears the Darlington.

but because the whole signal is very low in the first place. Um, and even with the gain, there's not going to be a huge amount of current, it just drives the Led directly. Also, you've got three volt minus a slight drop across the Darlington but that's it. It's very, very simple.

The other circuit is very dignified. it's very professional looking but just a very expensive. And the ceramic circuit board and everything and and the integrated circuit and everything. It just made it very complicated, but there we have it banned because the metal case but actually contained quite a sophisticated bit of circuitry.

The Power: Tracer A live wire detection probe. Very interesting. Turns out, it was well worth taking apart. Very interesting circuitry.