I featured another one of these battery level indicators recently, but this one is different. Let's Get Down close to it. So this one is based on a little eight pin microcontroller on the back and the interesting thing is that you can choose from one to eight cells and it just uh uses a potential divider to basically preset the voltage divider for the uh, the number of cells and at the moment, I've got it set for 12 volts. Well, I'll just uh I'll just show you operating so I'll turn it down because it's set for the higher voltage.

it's actually a bit brighter and it's also, uh, going to go down a more controlled manner. so that's fundamental there. And basically the battery outline in red and then four bars in green lighting at specific thresholds. Okay, right.

I can cut straight to the chase here because I've already taken the pictures and reverse engineered it. So here is the circuit board zoomed up and I shall just focus down onto this. So we've got the incoming Supply and it goes via a polarity protection diode, a standard diode to a three volt voltage regulator the three volt voltage regulator basically. then Powers the LED outline and also has a common resistor for the bar.

LEDs and it Powers a microcontroller with a little decoupling capacitor local to it. You have these bridgeable soda pads and they supplied it with just a single cell bridge but also a convenient splash of solder over the cell 2 which was bridging them which would skew the results. I removed that before I tested it and that connects to an array of Fairly Precision resistors. Noting that they've used the ones with the O1c and 47c designation that you have to look up uh, to remember.

it's not as easy as just looking at. say for instance, uh, this one 561 and going five, six and one zero 560 Ohms, which is what that one is, but it forms a potential divider with this resistor. this 10K resistor down here O1c and that feeds the input pin of the microcontroller, which then switches the four bars. Let me show you the schematic.

Here is the schematic: I'll Zoom A little bit closer at the risk of just completely over zooming. So there's the incoming Supply the regulator which I that looks a bit scrawled because I Initially just wrote in five Volt out of habit it's a three volt voltage regulator. It's called a 6513. Now it's worth mentioning.

the regulator has other numbers on it tb501g that drew a blank, but 6513 did find a regulator with the same Pinner Hp6513. It's notable, it's rated up to 40 volts. This is useful because if you set it to the highest setting here, the potential voltage is going to be eight cells times 4.2 volts equals 33.6 which is quite High I Mean it's within the rating of many regulators and it's uh, good that the current consumption of this circuitry is quite low. It's about 4.7 milliamps.

Um, let's work that out. Four points. So imagine it was. hold on.

Uh, imagine it was the eight cells times. 4.2 volts equals the 33.6 minus the 0.6 ish of the diode and minus the three volt. Um, Bing dropped on the regulator. 30 volts to dissipate.

Uh times the 4.7 milliamps. .0047 milliamps equals a dissipation of 0.14 Watts That's all right for this little regulator, so it's not going to get baked with the eight cells. Just about the need to do the maths right there. Turn the power supply off.

Sometimes it whistles at an ultrasonic frequency that somewhere you can hear, but I can't When it's up near, that's a range. So there's a three volt regulator. There's a little decoupling capacitor that's actually over next to the microcontroller. There's the resistor that's in series with six LEDs to light the outline of the sort of battery outline, noting that resistor and the LEDs are in the opposite position.

but I just drew it that way. It doesn't matter as long as the resistor is in line anywhere. it limits the current through them and then one common resistor for the four LEDs that have their negatives connected to the microcontroller. Then we've got these uh, this resistor chain.

So say for instance, you had a three cell pack is that had it configured there You'd link across here and that means that the incoming Supply would go via Uh 49.9 K resistor and form potential divide over the 10 key resistor which would then go to the microcontroller and it is just programmed internally with the thresholds that it will switch to LEDs. There is a slight delay suggesting that it's kind of applying a bit of air software filtering in that, but it's missed one trick. and I think this would have been really handy. Um, what? they could have done it? As the voltage increased, it was one two three four until all the LEDs are lit.

What it could have done if the voltage kept increasing and it went above the programmed Uh sort of voltage thresholds by a significant degree. It could start flashing the display to actually tell you the battery was potentially being overcharged. That could have been a useful feature. So the fact this has these Uh sell thresholds optimized for Lithium means that unlike the other one I featured recently with the Op Amps, you can't just change resistors and function it to a different Battery Technology That has to be done the microcontroller.

But for reference, the voltage threshold to operate that the single step with a single cell was above 3.4 volts, the second step to be above 3.55 The Next Step Above 3.7 and the full charge. the four bars above 3.9 and that creates roughly to what I was getting the three cell which is three times that, roughly 10 volts, 10.7 11.3 and 12 volts. It's quite a useful thing though. that's uh, very handy.

It's just basically a two-wire connection to whatever pack you have, and it can be used to give a rough indication of the uh, the current charge status because Lithium cells are fantastic for the fact that you know it's a fairly precise voltage for a specific state of charge, but that is it. Very clever. Very neat little unit. Um, quite a smart layout as well.

Very easy to reverse engineer thanks the fact it was all done by the microcontroller, but that's it. The more is it more sophisticated? the the more versatile Um battery level indicator for Lithium cells of up to eight cells.