All right. See these things pop you up on eBay Quite a lot. So I thought I'd buy one and analyze it. So let's get down close to this because it is quite small.

It's a battery level indicator and it's got the outline uh, continually illuminated. and then it's got the four bars to indicate the voltage thresholds of a discharging or charging battery. And if I turn the voltage down, you'll see the the pop-off one at a time. But you'll also notice that the whole display gets a bit dimmer.

That's simply because this is the lower voltage version, and even at this at a lower voltage, when it's cut off at just above three volts, you can see that outline glowing. But this would actually be brighter on a higher voltage unit and you'll see why in the circuitry. But if you turn the voltage up again, it pops back into life and it gets bright. Okay, right? I've already taken the picture for this so we can go straight to the chase here.

I've already reverse engineered it because it's very exposed. nothing to really take apart because it is just a beer module. Here is the schematic So well, not the schematic. This is the uh, the circuit board.

The back of the circuit board. Let me try and get into this without getting too close. So on the back, it's got an Lm324. This is nice, No microcontrollers.

It's a standard thing, but it's also and I've drawn this on the schematic. It's also got a position for a voltage regulator uh, resistor to take the load off that extra recovering capacitor. And it's got polarity protection, which is nice as well. There is something I'm not sure about right down here.

There's possibly an LED extra LED indicator. or maybe it's from another design, but it just seems to have a resistor and uh, that's it to power this. So I'm guessing maybe it is an LED. Maybe it's a switch that when it's pushed, it would light up.

Or maybe it build it and you'd push it and it'd show the voltage levels? Not really sure. Maybe I should look for other modules, but the gist of it is there is a voltage reference here. There is a chain of resistors here. It's quite a lot of resistors, partly because some of them are doing the LEDs and uh.

things worth of note: there's two common positive connections on the display. One is for the outer LEDs so they have their own resistor and they have their own positive. the other one and it's actually powered directly from the input to this. I'll show you in the schematic.

the other one is for the segments which are powerfulness. Um, not much else to say about this. so let's cut straight to the chase on the schematic. here is the schematic bit bright, but that's fine.

So the incoming supplier goes through a shotkey diode for large protection. This is good. We like parietal protection. It then goes straight to the battery symbol with our 1K resistor in series and This is why if say, for instance, this was monitoring your lead acid battery, it would be 12 volts come in and it'll be powering that directly.

This is actually six LEDs chips to actually make the outline glow, but that would be fairly bright all the time. In that instance, then we've got a current limiting resistor and a 431. The 431 is a classic component. It's that little component right up there Tl431431.

It's cloned to death. It's a 2.5 volt voltage reference, but because it's got this reference pin here, you can actually use a potential divider and you can make set it to any voltage. and this is commonly used in the feedback circuits of switchboard power supplies. It's one of these things that the 431 is a generic chip.

It's like a really standard chip and it puts out that 2.5 reference because the reference is tied straight to the positive and that gets divided down and it provides a common reference to all the positive inputs of the Op amps. Because this is a quad or pump chip. The Lm324 very standard, very cheap. It's also bread and butter component.

Then there's the option of the voltage regulator, which if you look at this dotted line here, this is actually linking the whole voltage regulator section out because if you can't really regulate 4.2 volts down much more, particularly when it's going way down to about three volts, but there's a resistance used with it. The resistor in series is supposing. you were maybe monitoring 24 volts, you might want to take some of the loads The Strain off the regulator. in terms of heat dissipation, by putting a resistor in series, it will dissipate some of the power, drop the voltage a bit, and then the regulator can deal with the rest.

In this case, they don't have this capacitor, they don't have that resistor and they don't of that regulator, and they just have a link straight across that then provides the incoming Supply or in the regulated case, the regulator supply to the Lm324 and also to the LED indicators. The input also comes to this divider voltage divider. based on high Precision resistors. The resistors have values like um 3oc that's the 20K resistor 680 ohms and then 71a is actually 536 ohms.

It's quite fine-tuned because these are crucial to the voltage levels, but they're set so that the voltage has the voltage on the input. It varies with reference to the reference voltage here. Maybe I should put those little dots in as well. Uh, the purpose of the Op amp.

Our comparators could do this as well, but the Op Amp it compares the voltage between the two inputs a plus and minus, and uh, when one goes above the other, uh, it will change the output State according to the polarity they're connected to, and in this case, when the voltage is falling down, the output was negative and the Uh should I say the output goes positive and the LED actually goes out because it's when it's negative. the LED is lighting. So we get the divider here and it's set so that uh, the first LED lights above 3.3 volts, the second LED lights above 3.5 volts, the third very close at 3.6 volts I Don't know if this is just because the increments my power supply are quite big compared to the tiny variation voltage of our discharging lithium cell, but the fourth LED for fully charge shows above 3.9 volts, which is reasonable enough. That's about 80 percent or more.

So it's sensible levels, particularly because, uh, when this one goes out, the second ones, when there's only half of them lit, it is roughly 3.6 volts. So that is pretty much half charge in the Lithium cell, and the resistors in this divider will be chosen specifically to match the uh, the incoming Supply voltage. There's say, for instance, if a sealed lead acid battery, it would show fully charged probably about 13-ish volts, and then progressively down. it would basically be fully discharged about 10 volts, perhaps because you don't really want to discharge them too much below that.

So that's fundamentally it. Excuse any crookiness in the voice I've been traveling and I've caught a exotic bug probably? or a cold one of those things. It is exotic at times. Um, quite high value resistors 1 K5 that that limits the current through the LEDs and output, but also because the voltage is falling with this particular one.

Because it's not regulated, the intensity drops quite notably as well as you spotted. If this had been say for instance, for sealed lead acid battery just a single one, say 12 volt ish, this would have been a regulator probably for maybe five volts. and uh, that would have meant the LED intensity was constant all the way down to the bottom. and there'd be a bit of variation in that instance in the battery symbol, but having said that, it's only going from 12 volts down to about 10-ish volts, so it's not going to varying brightness much either.

Quite interesting. I wonder what the upper voltage of these is? I Wonder if they go to say, for instance, a Jcb's 24 volt system with a two 12 volt batteries in series? I'll maybe have to look that up, but that is it. It's very simple. it probably does offer if you've got the skills to do so customization for specific voltage levels, but as it is as these are supplied quite cheaply.

uh, they've got these values pre-programmed in just for specific applications and that is it. It's a very nice little circuit actually. I Like the fact that the module has up, let's go I grabbed this I was going to turn it over. Well, that's not going to reveal much because uh yeah, this is just one side.

the circuit board I Like the way the module here. it's a dedicated module called. um, try to read that. Yes, Spb KBS 10 and it is specifically designed for this application.

It's like a sort of seven segment display, but it's purely designed for battery indicators. So there we go. If you have an idea of what that little switch at the side is for that little Illuminator or if it's a different applications of the module, let me know. I'm not really sure maybe I'll go and actually stopping these and look online.

That would be quite a good idea, but that's it. Interesting that they've got all those component positions as well for the other functions and other voltage ranges. Quite a neat little module.