Through the magic of buying 2 of them...

I'd heard of tri-state logic but I hadn't heard an explanation like this one, especially a real-life one. Many thanks!

I'd like to see you find its actual limit! If it doesn't pop at 500V, keep going.

We should have a BigClive binge watch and take a shot every time he says ‘One Moment Please’ 😂

dude I love this channel, this guy explains everything so well...

I always wondered about the thin poly cover over the segments, so thank you for explaining it was for potting, and can be safely removed.

On multiplexing and flickering: The most glaring example that comes to mind for myself is the old radio stack in propeller driven aircraft. Not only multiplex a lot of 7seg. displays but the flickering gets amplified by the not so stable onboard power supply and is heavily influenced by the motor's rpm. First time seeing this, i thought the thing might come apart any moment now. It is that kind of flicker you only see through a camera... well, usually. That flickering was visible to the naked eye.

I have a few of these in a fuse box I built for a solar circuit. They work well enough for low voltage applications and give a good indication of what's happening with your stuff. You're absolutely correct that they should not be used for high voltage without at least a fuse on it. Bad things are certain to occur without a fuse.

I use one of these for several years now to monitor the grid voltage. I also bought 2, as I was expecting them not to survive that long. But it still works, and also still shows the same value as the fluke meter…

I have multiple of these on my distribution panels and equipments to check for low line condition that happens sometime in winter. The precision is not that good but okayish for basic troubleshooting. If it says 200, it's 195-205 and it's a pretty low voltage for mains AC. It also have the advantage of adding fancy LED displays everywhere. It looks good, it display things, glows in the dark. Nice addition to any electrical equipment.

A minor correction, the pin isn't left floating. Setting a pin to an input set it to high impedance essentially stopping the current from taking that route. When a pin is set to an output and then set low the pin is then able to sink current. Leaving controller pins floating can, and often does cause a reset of the chip. A few years ago i built a clock face with 182 LEDs driven from a single 28 pin picaxe controller. Took ages to assemble.

I like those little low cost digital meters I own several. That stated only for low voltage applications. I don’t totally trust the reading without comparing to a calibrated Fluke DVM. Good information about which color LEDs will last longest. Thanks for another great video Clive.

This guy is my go to electronics site. Wish I understood the principals better but this is a lot of fun to follow along.

I've got a few of those little Chinese gizzmos and the seem to last a while, I use the thermometer ones the most with the two little batteries in the.... for $2:00 you can't got wrong. Thanks B C these videos brighten up my day. Cheers from Aussie 🦘👍.

I have purchased similar voltage displays intended for 3-24vdc and ~9-48vdc. One was intended for a car charging system monitor, the other for monitoring the power supply to a benchtop CNC machine.

I'm using the DC V and A panel meters, combined with a variable V controller and some leftover laptop bricks. So it allows 3 - 20 V supply & 5 A or so. The meters are 100 V and 10A.

Clive: im not going to hold this when I plug it in. I don’t trust such thing. Also Clive: uses metal vise to hold it. Also Clive: come on temu I want more dangerous stuff.

Thank you for including the diagram & explanation on multiplexing. It was quite understandable in a very efficient amount of time.

Thank you for explaining the tri state driving of the display.

Some of these don't have the calibration pot on the back. I always check the pictures before I buy. I get this form factor for volts, amps and temperature. Fun little devices. :)

The current meter version also has a zero ohm resistor you can remove to isolate the meter ground from the equipment ground. Pretty handy

I have used a few of these style as well as the ones with the amps. they work just fine on my home made power supply and other things.

These work well! I am not an expert in circuits like this guy but used several of these along with ammeter combination displays in my diy projects and they are quite reliable too!

Charlieplexing is so cool. My first encounter with it was for a 16 segment display and I didnt have any references. It took me forever without references to figure it out, and then the characters.

When I was young, these were only available as output units with a 200mV input range and separate power pin . Anyone knowing Ohms law was expected to know how to wire it up to resistors and opamps for whatever needed measurement: Volts, Amps, Ohms, Watts or even physical stuff like temperature or pressure . 199.9 mV in would display as 1999, decimal points could be wired at will .

Used these in three Landrovers ... worked well and very robust. Absolute accuracy was always a bit unknown, but used as a comparator between battery only, to battery with engine running, and running under heavy loads (winching for instance) was invaluable!!

I got the 1.3V to 30V version of this for my analog bench PSU. It works perfectly. 👍

I'd be very curious to see an extreme slo-mo video showing how that IC individually lights each segment in the display.

Yen years ago I would have no Idea what you were talking about. But in 2023. Thanks to the big guy, snd a friend would knew Less than I though. Smart, but people only know what they know... its it's sufficient to what they need. Nothing has taught me more Than what I need to know, than a gentle bear a half a world away. A man I will always respect. A guy With a beard i consider a friend. That has taught me enough to understand what he is talking to be about 10 years later

I have one of these that reads DC 12+ volts and amps. I used it in a battery charger after the factory analog amp meter busted. I checked it with my fluke and it was close enough for government work as is. Been working great for about 5 years now.

I have this one and its pretty good, you can just power it from another line where that big resistor is and it will do 0 to 500v (although i havent tested it at 500v), i planned to use it for a variac

Ha! This is the volt display I have on my tattoo gun. The whole build is very grey market, but you answered a load of questions about this weird-ass and kinda charming 3 digits. Cheers BC!

Thank you for the video, I haven't used the A.C. meters like this, but have a few D.C. meters.

Standard microcontroller, as those often enough have a built in ADC, oten enough a 12 to 16 bit one, though the 16 bit is really only usable by doing a lot of averaging over time, as the reference voltage in them in invariably the positive supply rail.This one likely has a 12 bit converter, and the bewtter versions use a TL431 reference to provide the 5V rail, often with the capacitive dropper having an intermediate 12V rail, so that the MCU has a better supply. The voltage is read because the input pin also is set to be an interrupt, the MCU waits for a zero crossing, then samples till it reaches a peek on power on, and thus sets a calibration time for this power on cycle, and then simply has the sample loop use a counter to wait this time after interrupt, and read the voltage, as the pin is also internally connected to the ADC on chip. Then the main loop takes this voltage, and uses a look up table to get a display voltage, and passes this through to the Charlieplex driver, which in turn converts it to a set of 7 segment numbers for the whole display, and passes that to the pin driver, which then runs through the setting for pins for each display. Flicker is mostly from beat from internal oscillator running against mains derived interrupts, as this takes the main out from the loop to run the setting of the one internal timer, and this in turn does another interrupt to do the ADC sample, and convert to a 7 segment block, that is in turn left for the display main loop to show as many times a second as it can. That display is a standard part now, used in many places where you can use a 3 digit 7 segment display, with each having a decimal point.24 states out of 30, so there are some displays using the same layout that have the 6 as annuciators to the side, or the top.

Great find friend!

I like the ones that come with both volts and current display in one module, and include a small hall effect current sensor in a ring wire-passthrough package. So you get both voltage and current display, but even more cool is that the current sense is totally isolated.

On these meters at least the 12v models i use, the little 0 ohm resistor is just a link between positive and the signal pin. with the link in place it will power up and read the voltage with the link removed it will just power up and you'll use the signal pin to get you voltage reading

The Vice of Knowledge !!! (not seen you in a while)

Thanks for responding to my query😊😊😊

Wow this is amazing

I have a couple of these in 2.4-30 volt installed in my pickup truck and it's very handy.

Instead of the clear film covering the front of the display, they could use a non removable colored film to hide the unlit segments and improve readability. I've seen some vintage LED display have that.

Fortunately, Clive warns us: "light back right now so watch your eyes" only to reveal the vice of knowledge holding a miniscule volt meter which couldn't escape if it tried. See, this is why I watch, I laugh loudly!

I use a couple of AC volt/current meters to monitor our back up generator. On this side of the pond each leg is only 120V AC. I agree with you I would be nervous using that widget on 500V. The ones I bought work so I never opened them up to check the circuity.

Cool. Thank you. Keep working, good luck to you.

You just now we need to see it at 500 volts. Nice, the vice of knowledge making a cameo appearance actually holding an item, not crushing a bit of tat. Interesting little item 2x👍

Fun fact; your peripheral vision is much quicker than when you focus on something. that's the reason why flickering lights flicker when you look somewhere else, but when you look at the light it stops flickering. This of course is so that you quickly notice a predator moving towards you so you can react faster.

These are pretty reliable AND durable. Only the "better brands" have the little pot, and that alone makes them worthwhile. As usual a drop of contact cleaner goes a very long way to promote accuracy / reliability, and with only modest care, these will last decades. We use them on our solar bank just to let us know how things are going, and with a simple shunt ("Usual Suppliers"!) these make excellent "Ammeters" too. Worth putting an additional decoupling cap. in parallel to the 470uF cap., since that appears to help stability (and durability too!)

I only use these type for 2 AC lines...the other 16 are for DC measurement...got a lot of different batteries & charging combinations on my systems so I keep a close eye on each to make sure everything is doing what it's supposed to do :)

630V DC capacitor for 500V AC? That's 707V peak. They also use a 600V brigde, which would be completely fine if they weren't dumb enough to put the 56 ohm inrush resistor after the bridge. This way, the worst case bridge voltage on inrush is 707V (turned on at the peak of sine wave). If they put the resistor before the bridge, the bridge would never see more than about 5V.

I purchased a few of these that also includes amperage (in a smaller green 7 segment display)

Charlieplexing, yay! That's a very nice way of controlling multiple LEDs with a limited number of control lines. Precisely, the upper limit is n²-n LEDs (a reverse-parallel diode counts as two), where n is the number of lines. It relies on tri-state logic (high - sourcing current, low - sinking current, input / high impedance - no current flow). Unfortunately it's prone to LED failure as it'd create a current flow path through multiple other LEDs if one of them failed open, or could blow the chip if it failed short. That's why it's best to add serial resistors on chip's control outputs.

I have been looking for something similar to add to a disability scooter 24v battery pack .Very interesting, thank you

09:00 - true it is an AC voltage going into the IC input, but remember the gnd/ref. for the IC is after the bridge rectifier, thus it is a pulsating DC / Halfwave sine, and just measures the peak and scales with the pot. to correct AC value

I love these. I use one on a ammo can boom box powered by a lipo so i dont over discharge it.

got a few of these running in several panel since years.

The biggest issue I have noticed with most of these panel meters is that the burden on the circuit for the few variations I have is a bit on the high side so when you are measuring voltages driven at a low current these meters tend to pull the voltage down quite substantially even if you are providing the power to the meter on a separate input.

I could absolutely use these displays for example together with a Variac or Dim Bulb current limiter to get a better view of what´s going on at the output

The version of this I have has a current sense shunt and a Volts/Amps display. It's pretty much identical otherwise.

I wanted to add a similar thing (voltage and current) to my variac, but when the voltage went below about 40 the whole thing turned off. The hack that worked for the kind I had, and would probably work with the one Clive is demonstrating is this. Lift the hot leg of the capacitive dropper and attach that to full power (pre-variac) so that the meter always has enough power to operate. The voltage to be measured is still as originally applied. With enough operating power the meter goes zero-to-max.

I found some little meters like this which mount in a standard electrical work box knock-out hole. They have several safety agency markings on them, but I’m not so sure China, Inc. isn’t fibbing about the safety certification. I also found a cool little meter which has color coded readouts for AC Volts, AC, current, elapsed time, Watts and Watt-hours. The meter came with a little current transformer to slip overt one of the load leads for getting the current reading. The readings are held in memory until a reset button is pressed. I mounted it up in a plastic work box with moisture resistant gland seals spliced into an extension cord. Very neat and only about 15 Dollars US for the meter.

Always good.👍 👍 👍 👍

I was somewhat surprised you didn't connect it to your insulation tester like you did for multimeters a little while back.

The battery charge indicator ones with voltage are great for lead acid

There are several current paths between any two of the LED driver lines. For instance if C and D are driven, current can go from C to E to D (and 3 other equivalent paths, along with longer ones like C->E->F->D etc.). However, all but the direct one have more than one diode in series and so draw almost no current as long as the driving voltage is less than twice the forward conduction voltage of the diodes.

a clive video

Wanna know a trick? Cut out a piece of automotive window tinting and stick it on top. This reduces glare and adds contrast. Kind of makes the 7 segment display feel like an oled or crt screen! There is a good video about it here on youtube but I forget the title of it. If you do this, make sure to make a little video of it.

That white box you’ve got looks really useful. But also stupidly dangerous lmao

This dubious meter I don’t trust not to electrocute me won’t stand up straight to camera, so let’s put it in the (metal, conductive) vice of knowledge 🤐🤐🤐 Thanks for the nostalgia mention of Charlieplexing - this takes me back to the 1980’s when I was studying for my HNC in Electronics - yes, I’m old!

😂 awesome I just bought two of the 4 digit display version of this 0 to 300 volt DC... they also do a five digit version for about £3.50

There's a 12v one as well and they work okay.

These only are accurate over a small range near where you set the trimpot. I found that if you set it at 240 it is way low at 70. And if you set it at 70 it is way off at 240. Seems to be very non linear so not usable for any kind of instrument reading a wide voltage range. They make lower voltage versions that have this same nonlinearity.

I have a bunch of those snap-in digital panel meters but, they're only supposed to do 0-100v max. 500v is crazy for those cheap things! I wonder if they think "well, we'll put a 600v cap in there so we can say it handles that." 😕

I used a Volts\Amps version of one of these to upgrade my ancient 1980 Absaar 12v battery charger from its old moving iron ammeter. Works really well and looks cool with the blue LED display. The only problem is it showed my battery charger only ever threw out a fraction of the Amps it was supposed to do LOL :o)

If each LED had its own resistor I suspect you could drive a whole column at a time, provided that the voltage does not exceed twice the voltage drop of the LEDs. Otherwise the current can start taking alternative routes across more than one LED in series. If the voltage does exceed that level (which does appear to be the case here) you need a resistor for each line and drive the LEDs one by one. I suspect the latter is going to be the best solution most of the time.

Pro tip: Use isolated screw driver for calibration pot.

There is a variant that shows battery levels on 5 segments, it could possibly have the same circuitry with less multiplexing.

I like to use these meters for measuring the battery voltage in mobile applications like powering my amateur radio equipment when on the road. But I only use meters for lower voltages like up to 30 volts. Too afraid to kill myself when handling mains voltage. Not trained in it, so leaving it up to pros like you.

Can you imagine trying to set the calibration on that meter with that small pot? A good one would have a multi-turn in its place, as they are cheap.

I got a similar looking display on AliExpress a couple of years ago. Mine had the same 2 wires and same connector, but it also had 3 thicker wires and a similar 3 pin connector for them. I'm not sure what those were for. Maybe one set of wires powered the display and the other sensed the voltage. I never did use it for anything.

Hey Clive, thought you might like to know that Toolstation have a range of integral high efficiency bulbs now, 806lm at 4 watts £4 that's more reasonable than Philips.

The tiny connector is normally used for akkus up to 6 V in RC cars/models or mobile credit-/debit-card readers. 🤭

what would have helped me was how to hook up the amps meter with this. Got it now. The info was hard to get because I didn't know what to ask for. building these into power supplies without a meter. I would not trust these at high power. 5- 15V and 5A is about all my max confidence in these units.

i should get some of these, i had some nice 0.1-99v but they have since died on me through abuse/neglect

Are you sure it's Charlieplexing? To my knowledge, the cathode (or anode) of each segment is connected to the cathode (or anode) of the corresponding segment of the next digit, and then brought out as a pin. The anode (or cathode) brought out as a pin for each segment. To display a particular number, say 250, first the microcontroller would pull up/down the pins needed to make the number 2 on any segment. Then, the microcontroller will pull down/up the common anode/cathode of the digit which should display the number 2. It would then turn off that digit, change the other pins to show 5, then turn on the pin for the next digit, and so on. Great video, and I liked the tip about spikes passing through the Capacitive divider.

These things is evolved from 3 pin to 2 pin only, also can have much higher tolerance of voltage.

I think the plastic film is actually so that pick and place machines can pick them up with a vacuum head

AnTai? What happened to the HOPI?

My 1st computer had a display similar to that. But it had jumpers on the back. I could change it from showing 33 mhz to 99 mhz just by switching the jumpers around.

Nice

That 0 ohm resistor shorts Live with Signal to display the supply voltage. If you want to use separate measuring input, then remove that resistor and connect an additional signal wire to the SG pin. This my opinion based on 0.28 inch DC Voltmeters. Not sure about this one.

Not mentioned... I think clive is testing us... Is that the 2 back to back leds are not in the same segment of the display but in seperate segments. An extension of this could be to use one more 'Charlie Plex line' and use both red and a green led back to back in the same segment and then you could have a tri colour display.....

The same one was on my variac, they'd used the wrong resistors than what was stated on the board, it was giving me hugely wrong voltage readings, so I had to remove the smd ones and try and jamb on some metal film ones to match the stated value, low and behold it came to within a half a percent of Mt multimeter! I also realised the downside of the digital meters, they take time to react, and if something happens suddenly, there may be no warning or indication of things going on with a voltage spike, I came to the conclusion, they're fine for dc, but for ac, go analogue 😂

Charlieplexing !!! Who knew ??

What happened to the Hopi meter? The new AnTai looks like the same thing... was there a bang?

so this is an average-responding dvm instead of true rms? if so, seems unwise to rely on it with questionable (solar 'pure sine' b.s. or other inverter / rectified or multi-phase) sources. cool vid as always, thanks

Mystery resistor, technical term is *mysteristor* - You're welcome ^^

Pile O’Stuff did a video on one of these (very similar if not identical) devices which he installed in a Variac for use as a bench supply. IIRC the circuitry, and his explanation of it, was the same as yours right down to a diagram he drew to explain Charlieplexing. (As usual your diagram was easier to look at). I find it surprising that Charlieplexing is not more common given its parsimony with the number of traces needed and so forth. Tristate output logic isn’t even required if you’re willing to include a matrix of diodes to do the steering.

i have this installed for a voltage meter on my motorcycle.

Id love if you could check out the "volty switch" leatherman 3rd party voltmeter for the leatherman bit exchanger ,turns your leatherman into a voltmeter ,i really want to build aomething similar but something that goes up to atleast 60v