Let's take a look at the digital panel voltmeter. I'm going to zoom down this because it is quite a tiny thing. although it does a fairly big digits. can't remember the size of the digits, but it's decent and and this thing is rated apparently from 70 to 500 volts.

I Have to say with a little connector like this, I'm not really sure I'd really fancy trying it at 500 volts, although certain you could put a small HRC fuse in line with that control circuit fuse. now. I'm going to grab the Uh tester here and we shall test it. So I shall stuff the wires in and then turn it on without actually holding the time because I do have a lack of trust in such things.

so I'll plug this in there. put it up like this. This one, incidentally is red. There are other colors available, but I chose red just because the red LEDs have the longest set of lifespan.

So that says 250 volts. Don't think that's terribly accurate. Oh, there we go, right. I'm going to carefully hold it.

It's not that bad for brightness either. By the way, 245 volts now see the Shimmer the flicker that is the multiplexing and if it looks a bit odd, it's because it's using Tri-State Multiplex I Can tell that just by glancing back and seeing the pins. But to the naked eye here, it's pretty good. Let me show you what that looks like to the naked eye one moment and that's what it more or less looks like.

I Would say that camera is still showing a slight Shimmer but I'm not seeing that at all. except when I swipe my eyes about and then you can see the slight multiplexing just because the way it works. Technically speaking, only one segment is lit at a time. Okay, tell you what.

I'm bring the light back and then we'll take this apart. I'll bring the light back right now, so watch your eyes, the light is back. H I've connected to the anti to get a better reading of things like uh, the power factor and stuff. so it's power rating is about about2 let's say.

3 Watts it's current is 27 milliamps and it's per factact is a really low 04 but that's just because of the way the circuitry works. It is a capacitive dropper. Okay, right, let's unplug that and see if we can hike the circuit board out of this. So I'll put that down there.

put the vice of knowledge out of the way I was using that just to temporarily hold it. So the way these uh circuit boards are normally held in here is these side tying. So I have to very carefully try and prize the circuit board out while uh, pushing this little tanging back and that can be quite tricky at times. Some of them are very, very tight indeed, which is good in a way.

It stops it being pushed in accidentally. H that is not necessarily coming out too easy. Then let's try again. I Shall drag on the cable while lifting this up.

Oh that's not even com out like that. that is very tight. Oh, here we go Here comes the circuit board. As always, we have the clear plastic front in it I'd like to remove that.

that's part of the manufacturing process I Think they put this clear plastic film on and then po the resin into it and this stops IT dribbling out the front. so I tend to prefer to peel that off. not as it really matters because there is a diffused plastic in here. Um, so the circuit board has the drop a capacitor.

It's got a smoothing capacitor inrush limiting resistor. It's got a 10 potentiometer here and then the chip that's doing all the stuff in a rectifier. Okay, I'll take a picture, reverse engineer it and we can explore it more one moment. Please, Reverse engineering is complete.

Let's explore. Shel Zoom down into this sucker board a little bit and the sucker tree is powered by a capacitive dropper. That's a very simple, cheap way of doing it. There's a capacitor here that rations a small amount of current through in each half of the mean's cycle and that gets rectified and charges up this capacitor via this halfast inrush limiting strangely big resistor with a a low value.

And then there's a Uh Xeno diode which caps a voltage around about 5 volts. Under the capacitor, there are two hidden resistors, 750k discharge resistor, And a 2 megaohm resistor which forms part of potential divider over here. uh to provide a reference voltage from the incoming Supply so the chip can measure the voltage. The chip then drives the display directly with just six pins and Tri-State multiplexing.

There is a mystery resistor down here which I think might be a fuse. Not sure what the function of this is, but this Uh connector here has anti-tracking slots under it, which is good, particularly given how close the connections are together. but it also has an option for three positions uh, the supply and a signal. If you want to use the meter in a different configuration, the rating of the meter is supposedly 70 to 500 volts Ac.

Okay, let's take a look at their schematic because it will make more sense of this. Here is the schematic: Uh, I'll come up to this bit in a moment. This is the Tri-State multiplexing. So here's the AC Supply com on and it goes to the dropper capacitor 630 volt, 330 nanard with its discharge resistor.

cross it. It also goes across via the other resistor to the divider, but that limit current to the bridge rack far. There is this strangely low value Spike limiting resistor here and then there is the smoothing capacitor and I'm guessing this is a 5.1 volt xener diode because I measured 5.04 volts on the Ra and they tend to have very specific values and 5.1 is the closest to that. There is a potential divider based on the 2 megaohm resistor and then a rather oddly specific 4.22k resistor and then a what measures in circuit as a 3K potentiometer.

not sure the exact value without taking out the circuit that provides a divided voltage to the IC so it can measure the incoming Supply voltage. There is the position for capacitor for Uh filtering of that, but they've not included that. Uh at 240 volt, 245 volt, Supply voltage I measured a range by taking this potential to from one end to the other. Uh I measured a calibratable range of 174 volts to 3 3 volts which is quite a high range.

Actually, it made it very fine for tuning. but I did use a fluk meter to check the Main's voltage. It was 245 volts. I Tuned it and it took if you move it a slight, but you have to wait for it to average the value and then stabilize again.

But I tuned it to exactly 245 volts so it is reasonably usable in that way. Here is the IC which is an unknown IC I Don't know if it's a dedicated meter chip which would make sense actually. Uh, but there is the 7sec display with 24 LEDs and just six Lines video. Let me explain the Tri-State multiplexing that allows them to control uh, that number of LEDs with just six lines and I'll zoom in for this just a little bit more.

with Tri-State multiplexing, each pin can have three states. This is why it's called Trate. It's also called Charlie plexing after a Salesman who promoted it for one of the electronics uh manufacturing companies. But each pin can either be positive, negative, or floating and drive an individual LED and I Think they just drive one LED at a time.

They just take one of the pins positive and one of them negative. There are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 possible combinations of bridging these Uh pairs of pins and each of those has two polarities. so you could potentially have you inverse parallel the LEDs. So the 15 times those two LEDs gives 30 LED driving capability To work out how many you can drive from a given number of pins, you multiply a number of pins times the number of pins minus one.

So in this case there are six pins. 6 * 5 gives a total of 30 LEDs If they'd used five pins, it would have been 5 * 4. That would only have driven 20 LEDs and not been enough for the display down here. So as an example of this supposing, we took C positive and D negative.

The LEDs bridging those two pins are these ones here. and because the C was POS positive and the D was negative, the current would flow through this LED and that Led would light. If you swap the polarity, that Led would light and by scanning through all the LEDs individually, they can, uh, basically just control the whole display. but it does give that strange swirly, shimmery effect uh when viewed in the camera as opposed to different uh, the other multiplexing methods.

Now it's worth mentioning that when I bought this one, I also bought another one and given the it's missing this capacitor here which I would have thought they'd add. but having said that, they are feeding with an AC signal source which is quite odd. um, so a lot of averaging is getting done inside the chip. This Uh module is simpler than this one which does have a capacitor, a ceramic capacitor possibly for filtering, plus a diode.

um, and it's also potentially got another capacitor across the supply rail for taking out those spikes uh, that might occur with capacitive droppers if you get a a voltage Spike the Capac just turns, it acts like a filter and just basically pass it through and it can actually damage circuitry if that. Finds Its Way to the chip H This is why the cheap Chinese Paduk microcontrollers actually seing their data sheet. It's not suitable for use with capacitive droppers. They're basically covering themselves there.

and I blew up a pick microcontroller in my early days. an expensive ultraviolet Raz one with a capacitive dropper. So it's it's real. It's a thing.

But there we have it. Um, it's useful. It's calibratable. Um, it does the job.

It gives you a good indication of the voltage. Um, so in that sense, it's quite a cheap. meter. does the job.

It's okay. it's an all right little thing.