It is time for the final installment of the Audiferex Trilogy. Looking just at the circuit boards, there were more videos, but uh, this was just the circuit boards and this particular one. Let's bring the the full image in. This particular one was to select the previous one.

Very hard to remove from its Mount because it's got these very large pins with lots of heat sinking taking the heat away from the solder and it's a plated through hole so it was quite difficult to remove. Quite destructive. But I did remove it and got it out. So let's explore the circuitry.

It's quite interesting. This was a double nighter. It was quite complex to reverse engineer. So there are five connections.

uh, going to the battery one is the temperature sense connection that goes to not just the NDC thermistor and the battery to tell this circuitry the temperature, but also the battery itself. If it detects that it's got a low charge, it can cut off the supply to the NDC thermistor and this will detect that as well. so it basically stops US operating. This means that you can cheat these tools by connecting a resistor between one of the negative pins here and the uh, the temperature sensing a 10K resistor.

But it's not recommended because many batteries rely on power tool itself actually stopping using current when the voltage goes so low. They don't have that facility to cut the current off themselves. that's done by these mosfets in the power tool. So this was the 2040 volt battery system, and in this case because it's a 20 volt tool, they've literally just banged the two negatives together of the batteries and the two positives, so they're in parallel.

That's quite unexpected, but you know what? It's reasonable off the batteries because they're either used in series or parallel, and because they're kind of semi-balanced Uh, battery-wise certainly. Uh, by battery. Not necessarily cell balance, but battery balanced on the charger. It shouldn't really cause significant current flow when they're joined together like that.

There are two mosfets switching current to the load. There's a diode across that load. That's the two connections going out here. There's a processor, mystery processor, and then, uh, well.

let's just cut straight to the schematic Things worthy of note though: A Zener diode, a series of chain of resistors in a diode, and a couple of mosfets. This is the power supply sanction for the five volt power supply, using a simple resistive limiter. It's quite clever. This circuit is just in line with the tool.

The positive and negative come onto this board via these contacts and then go straight up. It looks for a current modulation when you pull the trigger on the tool, and that's how it knows to switch on. And when it does, it activates the circuitry as you'll see in a moment and that then provides five volts to this. And then it does the fuel enabling mosfets thing, and then monitoring for loss of use of the tool, and then it'll cut back off again.

It's quite complex. Other things worthy of note to this Led position which and resistor with the resistors not needed because the LED is not there, but they don't actually make sense in the circuitry anyway. as you'll shall see in a moment, there's another Zener Diode over here. There's one here for the five volt.

Supply There's another five volt one for a voltage monitoring Supply Not sure about that. You can. You can chime in with this. you can tell what you think it is.

Let's get straight down to the socket board. the full schematic. Okay, so I can fit this in okay and get maximum viewage because it's densely packed. So here are the battery connections.

the two positive connections here, the two negative connections and this Arrangement here is emulating the tool being connected to that so it's a motor in series of switch. In reality, it could be a variable frequency uh, trigger, but as soon as you turn it on, it's going to start passing current and that's what this unit detects. So initially, what's the best way to start with this? It's a complex socket. so initially, when you pull the trigger in the tool, it connects a positive reel the mosfets off.

So it connects a positive reel to this. Lane And this Lane would normally be gently biased to the zero volt rail, but uh, when you connect, build the trick in the tool. It takes this positive. and there's a capacitor here that allows just a small amount of current flow as it through this resistor as the capacitor charges up.

But it's long enough that it turns this mosfet on which is an end Channel mosfet pulling to the zero volt Rail and that pulls this positive channel that its gate resistors to the negative rail turning it on. So once this P channel mosfetch is turned on, two things happen. Well, just generally applies power to everything. but the power for the five Volt Supply goes through this diode through these three current limiting resistors three times.

150 ohms. spread the dissipation because it is simply a resistive dropper and then that gets regulated roughly to about five volts by the scenar diode to the couple of capacitors and that then goes to the processor. But it also goes to the battery monitoring circuit that also provides power via this red line here to a voltage monitoring circuit I think and then this circuitry here which might be monitoring the mosfets. You can chamin this and tell me what you think.

That's quite complex though. But so the sequence of operation here is that when you do press the trigger in this, the power goes is coupled via this capacitor. turns this transistor on this one on gives it the 5 Volt Supply the five Volt. The processor then provides its own bypass 5 Volt Supply via this diode and it can then bypass that and it can keep its own power supply on until it needs to turn it off when it wants to turn it off.

If it sees the situation, that tool has not been used, it can turn the take this Uh signal to this diode low and it will effectively let the system shut down. Um, it when you peel the trigger and it Powers up, it's going to monitor the battery. It's got the the pink box. Here is the NTC thermistor in the battery going to the battery's negative which is common to the battery negative here, but it's got a potential divider on this circuit board.

It's got a 10K resistor so you'll get a voltage which in normal instances will be roughly half uh of that five volts. it's going to be say about 2.5 volts that's coupled via this 10K resistor to the microcontroller over here. but via these pink pads and uh, if it sees that it's got a resistance in the correct range, the voltage is in the correct range are not too high. which might mean that the Uh battery pack is disconnect the thermistor and therefore it floats, allows it to float hand.

That means the battery is flat um, or it might be as out of range level. the battery might be too hot, uh or too cold and that will signal to the processor not to actually start the tool. But if everything's okay, it will then provide on this purple pin a signal will reveal this 100 ohm resistor to the two parallel mosfets. I've just drawn one here and they have a 10K pull down resistor and that will turn them on at the point they turn on effectively.

This line then goes to negative so it's just as well that is, uh, driving that positive. otherwise it would try and turn itself off. Um, things worthy of note here: I'm I Think this is for monitoring the voltage across the mosfets when it's turned on that this red line here is for current Uh Quiescent current reduction. It means that when the battery pack is asleep, this red line actually turns off and uh, effectively, it shuts down the processor by removing the five volt.

Supply It shuts down this voltage monitoring circuit and it shuts down this bit of circuitry and that bit of circuitry. because let's get the 5 volt Supply too. So it shuts everything down into a super low current. Crescent State when it's active though, this is presumably because it's a voltage divider 200k and 20K dividing it down to roughly about a tenth of the battery voltage and that is going to the process.

So that might be for monitoring battery voltage. Um, I Don't think it needs to know that that has been disconnected unless it wants to know that this is turned off in any way because then it's good control of that. It's a very strange thing it might just be monitoring to see if it's in a reasonable battery voltage range. although the battery itself would be monitoring that.

It's odd. The other bit of circuitry here that's of interest when this Supply becomes active, it turns on this mosfet which then allows this 10K resistor to couple up to that line and uh, there's another uh, zener diode here that caps it to a maximum five volts in a capacitor under very high value discharge resistor. And then it goes to microcontroller and it seems to be monitoring the voltage across the mosfet. Now my guess is that it might be for monitoring over current situation where if too much current was drawn, it would see a higher voltage across there that will be smoothed by this filter circuitry and then it will actually indicate the processor that maybe the mosfets have gone into thermal runaway or where the resistance increases.

Or it could be that, uh, there's just such a high current due to a stalled tool that it will actually see a higher voltage across the mosfet being dropped across the mosfet and it'll actually turn the mosfet off. The other thing I could do I'm trying to work out how it turns off. how does it know that the tool is not in use? and uh, I know that when you trigger this, it stays active for a while. but um, I'm guessing that ultimately if the tool is off, this will not.

This would normally be pulled down to zero volt reel. so if the tool is off, it'd still look as it was a zero volt rail. It may turn this mosfet off briefly and it may just look with this circuitry again. it may just look to see if there's a change in voltage because if it did turn this mosfet off and the voltage didn't rise, uh, it would maybe indicate that this, uh, the trigger had been released.

It's quite a complex circuit. It takes a bit of puzzling to work it out. It's quite a clever design. The little rectangular block here with the question mark is the resistor and Led position.

I'm not sure what was that going on there. The only thing I could think is that originally thought no, that doesn't make sense. It doesn't make sense why they've had that Led there. Maybe that's why it's linked out.

There is a distinct uh wire link just across that they have left the resistor and even though it's actually completely not functional anymore. Strange. I Wonder if it was just a change in design or a and circuit board design they used in something else that they just adapted slightly and maybe there was slightly different track layout and that was an actual active LED that Lit from the bottom of the tool pack so you could see what you were doing. That's kind of done by the Um in the drill, that's done by the actual trigger mechanism does that, But that is it.

Let me know what your thoughts are on this. The circuitry is quite complex. How do you think it attacks that the trigger has been released? I Think maybe it does pulse that most of that off briefly and just see how the voltage changed in that. but there is a capacitor.

They would introduce a slight time delay and if it was doing it regularly, you'd actually get a slight Jitter of the drill. Um, very strange, but that is it. It's quite a complex socket. Clever.

I Like the way it's very educational, the way they've got the shutdown circuit and how detecting a disturbance in that no matter what tool is attached. if it's a simple switch and series the motor or it's uh, in the case of this, it's a variable speed trigger that triggers uh, this to actually wake up, brings the power to the processor and then the processor holds itself on very interesting knit circuit. indeed. It must have taken some amount of experimentation designing, but a very educational, very informative,.