The classic Lithium Button cell the CR 2032 but there is also a version that can be recharged called the L 2032 and here is one of the Chargers Now you cannot recharge the CR 2032 I Don't recommend putting one of them in, but this one in one of Mouse's mini putor badges. Uh, this one is an L 2032 as written on the back is that even going to be visible it's it's not could be very visible as it. But anyway it is an L 2032 and the 2032 uh relates to the diameter and the thickness. So 20 20 mm diameter.

Let let me get the calipers here and I can prove that where are my calipers there? They are 20 mm diameter and 3.2 mm thick or 3.1 in this instance apparently excellent. So so this little charger takes a USB C input and it's this side is marked positive. This side is marked negative I Don't know if it's gotar protection, but the positive side is the main body of these cells and the negative side is a little sort of inserted disc. So You' put it in like this and then you get your lead this random lead and you plug it in and there is a hole here and it lights up red to show its charging and then after a long time it goes green and I wonder if there is that protection? Anyway, there's one way to find out and that is to open it.

so let's try and open it now. Uh, brief investigation shows. I Don't think this end opens and it looks as though let's just try and wiggle it. Wiggle it just a little bit ASD her as they say I'm not sure how this comes apart I Think this bit inserts in here is a spudger going to go in? The spudger is going to go in.

Is it going to delate anything? No, it's not. This may be tricky to open. Oh, it's open. Oh that.

I think that was using the metal as a little catch. Is this using an Lth? Oh, it's a very small circuit board. I wonder if it's using an Lt7 circuit board right? So I shall take a phot of this and we can explore it in Greater detail one moment please. Reverse engineering is complete.

Let's have a look at the circuitry. Nothing too fancy. The USBC connector only has two connections. It's not got any indication.

Back with resistor to the device that's feeding. Let me Zoom down this a bit that Uh is actually at load that needs powered. So this won't work with fancy uh power supplies, but it will work with dumb ones. Just a standard USB lead like say for instance this one.

It has a standard charge control chip much like the TP 4057 or the Uh TP 4056 but this one is called 57 B9 which would just be a code We have. The incoming Supply goes to this de coupling capacitor and then goes to the input of the chip. There is a current programming resistor 85c which is 75k. We've got a 1K resistor here and a 1K resistor here, going over to an LED with a red and green chip for Red for charging, green for finished, and then really, oddly from the positive rail.

This is strange. There's a bypass resistor going to the output 150k and then another decoupling capacitor on the output. The connections: The positive goes out on uh, these two tabs and the negative goes out in the back tab on the back of the circuit board. There, right? Let's take a look at the schematic.

Only one significant surprise. It's more of an oddity than anything else. So here's the USB Comm in and normally it would just go straight to the chip, but in this case, there's also one going to that resistor over there. Strange.

Maybe for stability? Maybe for some other reason, maybe a a design error, or who knows, there's a decoupling Capac across the input. This is good. There's the Uh feed for the LEDs with the two 1K resistors for the LEDs. There is the programming resistor going to the Zer volt connection on the chip and then the output has the capacitor, but also that strange resistor.

Which means that theoretically, if you connect a Lithium capacitor to this, there'll be a very tiny continuous trickle current from the 5 volts. But the difference is really 4.2 volts versus the 5vt supply. That's less than a volt. So it's going to be a tiny amount of current.

but it's odd that they've done that and then to the lithium cell. However, there's no reverse protection. What would happen if you put the cell in Back to Front There's only one way to find out. Let's do it.

So here's our typical shun: USB power supply and I shall plug this in here and it's showing. uh, no current. So I shall plug the lead into here and then I'll put the battery in the right way around the the lithium cell. so the lithium cell's in the right way round.

It's showing about 13 milliamps here. Let's Zoom down a little bit and make sure it's very visible. So now let's take this out and put it in Back to Front See what happens? Is it going to smoke the circuit? Will it make a connection at all? Nothing. then in the right way around and charging again.

It didn't seem to do anything H Is it actually shorting the cellout hold on. Let's get the meter in I should just zoom out for this. So I'll stick this round to the 20 volt setting. What voltage is on this cell? at the moment? We have 3.9 volts.

Let's put the battery in the wrong way around again and measure the voltage across it. 3.9 volt. still. but it's just not doing anything there and it's not showing current over there? Turn it round and it's back in AC I Wonder if it has I wonder if it actually has short circuit protection and the current is showing again? Uh, 14 milliamps, 13 to 14 charging and it's uh, up to 4 volts? Uh, okay, so it does seem to have some sort of built-in protection I'm guessing.

um I wonder how they Implement that. But there we have it. there is the little convenient uh Button cell charger for Lir 2032 cells I Think it can handle different thicknesses as well. but uh, the main thing is the 20 mm bit.

the 20 maybe 2011 6s would fit as well. and the current's not ridiculous. It's actually okay. about 16 milliamps.

um, which is the top? measured about 15 or 16. Uh, very simple and very functional. Just make sure you do put the cell in the right way around cuz it can go in both ways around. But there we have it.

An interesting little device.