You've probably come across these test screwdrivers before because they've been around a very long time. The circuitry has changed. It's definitely changed in this one. It's It's not even what's showing the picture in the listing, but the idea is that if you want to test continuity, if you bridge one end to the other, the little red LED in there light and also if you hold it near a live electrical connection isn't going to work.

yeah, it glows you. it's You can see it flickering slightly there just because it's picking up the sort of the AC signal. And likewise, you can actually stuff it right into a live electrical connection. apparently.

Let me just, uh, prize this open. And then it. definitely. It definitely lights brightly when it's uh, stuffed into a live electrical connection.

Not that I Totally recommend it because the Chinese have this very odd definition of electrical separation. Basically none. Let's Zoom down a bit because here's the interesting one. This one didn't work when it first arrived, and the reason for that was just a bad battery connection.

But I Get the feeling that they expect the batteries not to last too long because they supplied another little heat shrinked or sleeved stack of cells to replace the original ones. but this one has two LEDs and if I put a finger on it. that looks static to me, but it looks as though it's flash on off to you because it's got a microcontroller in it. But the look of it and it does have another LED And the idea is that if you say for instance, I'll wedge the safety thing open with the screwdriver.

if you're going to say neutral, just the green LED will light. but then if you go into being careful not to touch both at once here, if you go into the live the red LED in there lights as well. So it gives you a idea of not just continuity. And because if you go into Earth or neutral, it's effectively your reference to ground so that will just allay continually.

Much like you know, just when you're bridging it out. But that fact that, uh, it can detect that and it lights the two LEDs is quite interesting. So let's open them. I Shall actually use each screwdriver to open its rival.

Oh, that is a spring and it doesn't want to actually open. Yeah, that is actually want to spring back. Is this going to come out at all? It's all gone horribly wrong. Yeah, there's a spring in there and there's it's bringing up right? Let's head knock this out.

Here is the circuit board: I Can see two transistors. Now the classic version of this. We're reverse engineer this. the classic version that's used at Darlington.

Just a single Darlington transistor with a pull down resistor and then a safety resistor or two. I Can see those two resistors in the series here, but with pure separation. I Shall explore this further. Um, but this one is using two transistors which may be just configured as as that sort of rudimentary diamonds and I should put that one to the side so we don't mix the bits up and I shall go into this one which I've already had all because I had to open it I had to bend the Uh resistor lead or should I say is it that's just a wire lead over at the top because it just went up straight initially.

This one does not have much in it. It's got three little resistor type components. the two LEDs and the Mystery eight pin chip right. Tell you what.

Uh, let's get a close-up of these. I shall take a picture and reverse engineer them one moment. please. Reverse engineering is complete.

The screwdrivers have been rebuilt and were ready to explore these. See the pulsing green? That's just a an intermodulation effect because it is pulse of modulating. It's microcontroller controlled. Let's take a look at the Um the simple one first.

now. I saw the true transistor should through the side and I thought the brush could be the same I thought it was going to be what they call a Darlington In a way it is cascaded transistors but one is Npn and one is PNP It's quite hard we've got two resistors here to limit the current that could flow into it. These are kind of for safety, but to be honest I think I'd rather have had as better spacing on them. Um I just I prefer a good margin between me and the mains because uh, if you've got your finger in the end of this and it's just the circuitry between you and those resistors between a live connection and you're well grounded, it could be bad news.

I Prefer picker resistors Anyway, we've got those two resistors. We've got two transistors. The LED and I shall show you the schematic for this. It's very simple.

Here's the two batteries to give it three volt supply of the two cells. A battery of cells. The touch connection is connected to the positive side of that for a good reason. Here are the two resistors 12K and two Mega the safety resistors.

There's a tip you either touch with your fingers for continuity like this or touch on your live electrical connections or even hold just near electrical connections and the radiated field will be picked off and it'll make the LED flicker. Uh, so the first transistor here, which is Npn amplifies that small amount of current to a degree. it wouldn't be a huge amount to their amplification. Well, it wouldn't start up, it will start off the very low current and so I guess the application will here will be about 300 times.

That's what it usually is for these little signal transistors, but then that goes up and it's now. it's Amplified It goes into the base of this PNP transistor. PNP Transistors normally are connected to positive realm, so it's odd That this Led isn't down here. but I Get the feeling they may have done that deliberately, but because this, uh, the base of the PNP transistor is being pulled down by this transistor, it amplifies again.

She end up with a compound multiplication of that current in there and it's enough to make the LED glow. I'm guessing that because LED is up there. Um, as the as the LED lights up, the voltage across this uh transistor will drop and that kind of acts as a very crude regulator. It's very simple.

Now let's take a look at the other one. This is a bit strange. The listing: I Bought this from Uh, we shall turn this around. Either way, it's nice.

I've learned other way. the list here: I Bought this from showed this picture and if we look at this picture, it shows two transistors. It shows the two two Mega ohm resistors for the safety in the series and not sure, the diodes for maybe a Zener diode not sure and a resistor not sure that's for unless it was for one of the LEDs I'm not sure but these two transistors I guessed might be mosfets and then Channel mosfet in a p Channel mosfet with a resistor. a cross between Uh to the base and to to the gate of each should I say just to sort of drag it down but that's not what arrived.

I was hoping it was convinced and I was quite intrigued to see what the circuitry was. Instead, we've got a microcontroller which is just ludicrous in a test pen. so the microcontroller has the it drives the two LEDs directly so it's relying on the impedance of the well, the cells as well as the output Gates and it is also to control the intense to keep the current down. its pulse of modulating them to down about to about six milliamps.

The standby turn to the circuitry is ludicrous. The it starts off if it's been active. it shows a slight residual current about seven microamps and it drops to zero. I Couldn't measure it, but it is still active.

It is still tapping at that just to actually check the inputs. and then we're in a season input. It wakes up. Yeah, on the input, we have Uh 476 so that's four, seven, and six zero.

So that's 47. Mega And then we've got two resistors, one going to each of these pins. One is quite low value. it's 1.5 Mega Ohm.

The other is a ludicrous value it couldn't measure in circuit. it was such a high value of a hundred Meg ohm and I Think that's what it's using to detect just an ambient, say, for instance, just you touching it. It's only enough to trigger one inputs, but if you touch it to the mains, then the voltage high enough that enough current flows. It triggers a second input.

Um, and these will just have a pull-up resistor. Um, the yeah, that's it. microcontroller, two LEDs and two inputs from two resistors. That's fundamentally, let me show you that schematic.

Oh, note incidentally that the super high impedance input the one with the super high value resistor 100 Mega the track layer is a bit hard. It comes right up around here and back down. Don't know if that's for field sensing, it might be for field sensing. Not sure.

Let me just hold this up next to uh, that's the wrong one, hold up to next to no, it's just the green one that lights when I hold it up in the vicinity of stuff. That's strange. But here is the schematic. We've got the three cells creating a 4.5 volt battery plus 4.5 volts.

In this instance, the touch sensor is actually going to the zero volt rail. which means that these, uh, the chip in here will be pulling these up to this of positive Reel with that weak internal pull-up which I think these resistors have been chosen to be able to defeat that pull up in when the current is high enough uh, 47 Mega resistor and then splitting out into that huge 100 Meg ohm and the smaller 1.5 Meg ohm. And so the 1.5 mega mode with a high sensitivity input and it will just easily defeat that sort of pull-up resistor that tiny, uh, pull up current. but for the higher voltages it takes uh, that our voltage to be able to defeat the other input three via the 100 Meg Ohm resistor and then just two LEDs It's a super simple.

It's ridiculous that they've actually got a microcontroller in there. It's obscene, but there we have it. I May take a look out for other ones because, uh, they seem to be changing these the design of these quite a lot, but that's very interesting. They're not that expensive I don't really rate their electrical separation, but uh, if you ever use one of these, they're good for continuity tests and things like that.

but if you ever use one of these, I Do recommend not being in a well-grounded environment, not touching grounded metalwork while you're actually using them. I Just prefer protest lamps and stuff, but these are a good visual check for things like, uh, just live wires while you're just as a double check to make sure you have isolated it. Interesting things well worth getting and exploring. Quite unexpected circuitry.