Inside an LCD voltage tester (with schematic)

[@nigel-matthews]

You spoil your viewers (and Patreons) making these tear down videos even while you’re traveling for work. The behind the scenes videos of the show in the castle are fascinating!

[@zyeborm]

I'm kinda hoping Clive can use KZbin to retire, he'd have to be one of the few KZbinrs with around a million subs who still has a day job. Perhaps he has retired and is taking the fun jobs. Let's hope that's the case 🙂

[@nigel-matthews]

@@zyeborm he’s definitely one of the hardest working KZbinrs.

[@danedewaard8215]

Thank you for explaining this device!!! I bought one at the dollar store a few years ago and always thought it was a VERY STRANGE THING!!!! I may start using it now. Thanks again!

[@DieselTjuv]

We use these to test our electric horse fence. However, when testing an electric fence you need to make sure that you DO NOT touch the terminals on the end of the tester, since it will give you a proper shock :) Just touching the fence with the screwdriver bit alone is sufficient to make the flash symbol appear. Also, this is a much cheaper electric fence tester than a "proper" tester (and anything related to horses is for some reason at least 4 times more expensive)

[@thephilpott2194]

Horse eqpt: Yes- they assume you have enough money that a huge mark-up won't be noticed. All a bit naughty.

[@tin2001]

You can get digital fence meters for under $100AU (roughly £50) on eBay. You can get ones with LEDs for different voltage ranges fences use for around $20 (with actual ground wires instead of the user). There's also ones in the hundreds of dollars, which are no doubt more accurate and better built... But if you're just checking the voltage at the far end, a rough idea is good enough. I've just been using the back of my hand though. We can't find the actual meter.

[@DieselTjuv]

@@tin2001 Yep, I'm not interested in the actual voltage, just that there is voltage. Back of the hand is of course the cheapest option :)

[@davidfalconer8913]

A bit like " medical " stuff for old folk .... hideously expensive .... litter grabber = £15 , Poundland™ = £1 ..! ! .........

[@rjmun580]

You have an electric horse? Watt is its name?

[@sebastian19745]

I first have seen one of these around 1997. Then I got one and I used it and I found it very useful as a non-contact indicator but also as raw voltage indicator. As a plus, it have a small flat screwdriver. Since then, I had many, just because I used to lost them, but no one ever broke.

[@acmefixer1]

This suffers from the same problem a DMM has: there is not enough load on the circuit to determine if the circuit is connected or if the voltage that is read is from capacitive coupling. Say the breaker for the circuit has been turned off. The capacitive coupling from another conductor in the same conduit could make you think that the circuit's breaker is still closed. This is why professional electricians use a Wiggy with the solenoid that pulls the indicator to the correct voltage, and takes a few milliamps of current. Thanks, Clive. I think the cheap, little neon light indicators might be better for residential electrical testing.

[@thephilpott2194]

Yeah, i recall double checking with an analogue meter when working on a ring main that i was certain that i'd isolated......the DMM was coming up with phantom voltages from adjacent conductors.

[@drkastenbrot]

proper multimeters have a low z mode for that

[@straightpipediesel]

All of the Fluke DMMs for professional electricians or industrial workers have a low impedance mode. (Fluke 113, 114, 117, 87V). It's a solved problem, without having to resort to old fashioned techniques.

[@davidg4288]

@@thephilpott2194 I had that problem at my Dad's house years ago, there was enough capacitive coupling to show 80 volts or so on a disconnected circuit on an analog multimeter! This was in USA with 120 volt mains. My fingers showed nothing so I continued my work.

[@KeritechElectronics]

Had one in my old lab, nice for a very quick test but a typical neon indicator is way more reliable, and a multimeter is way more useful. This thing is so astonishingly simple!

[@maxmotion8470]

It somewhat reminds me of a fever Thermometer. Love your Videos and watched them for years, you inspired me to start studying Electrical Engineering last year! Thank you very much for your interesting Videos:)

[@kimvibk9242]

Let's hope the doctor doesn't mix them up...'You have a temperature of 110 V - take an aspirin and a resistor and call me tomorrow"...😀

[@poppy5525]

I think you're bang on dude. I reckon that the casing is literally an off the shelf part. Originally for dollar store thermometers, repurposed for volt meters.

[@RFC-3514]

@@poppy5525 - Are "dollar store (body) thermometers" a thing? That's the kind of device that is usually regulated (same as pregnancy tests, etc.) and sold only in authorised places. Though I guess they can sell them anywhere if they label them as something else.

[@dantronics1682]

@@poppy5525 actually the voltage screw driver was out before the thermometer,I have one thats I bought in the early 90s

[@markfergerson2145]

@@RFC-3514 All that's required is a disclaimer (printed in a font so small an ant would need a microscope to read it) to the effect of "not to be used to make medical diagnoses".

[@VarionJimmy]

Interesting indeed! Was curious about the Non Contact path. And of course, raw LCDs are always a bit mystical. It would be fun with a video about them. Perhaps how to (re-)use them for own projects? Or just an exploration.

[@wimwiddershins]

We had a gadget to remove the static charge on CRT screens that had a display that was powered by the discharge (little lightening bolt). Bit of a "solution looking for a problem" thing.

[@RFC-3514]

You needed to discharge static from CRT screens if you used one of those completely useless "radiation filters". So it was really a solution to a problem caused by a non-solution to a non-problem. :-P

[@Kitsaplorax]

I'd hope to see a destructive safety test with this. How does it react to 480 or 1 Kilovolt? High humidity might make it conducive.

[@markfergerson2145]

With an ammeter between the touchpad and earth.

[@mrbyamile6973]

@@markfergerson2145 I read your comment as "an amateur" thats probably also likely to happen 😄

[@markfergerson2145]

@@mrbyamile6973 Lol!

[@LarixusSnydes]

This would be a great fit for Photonic Induction, but BigClive also has a device to test the insulation between transformer windings.

[@BuyitFixit]

"I have dangerously defeated the safety shutter...." - I thought "Danger" was your middle name? :)

[@TheRailroad99]

Crazy how little components these are in this. 100% optimized to be economical

[@sadn0x281]

hence why it's so cheap xD normally i wouldn't buy it but it was so cheap i decided meh why not (it was $0.75 in my local store)

[@Gold63Beast]

Love you BigClive. I Never knew about print on resistors. Really cool. You learn something new everyday. 🙏

[@janami-dharmam]

I recently saw one set-top box remote that had the resistors printed on the green solder resist. The PCB was single side and made very cheaply (the battery leaked and one electrolytic capacitor went bad). The connections were all low resistance values (acting like jumper wires).

[@Electronics-Rocks]

So simple I bought one for my dad and myself from CPC back in the eighties. I lost my one year's ago.but now I have my dad's after passing. The back on ours is either welding or very well glued as even had it run over by cars. I found very useful throughout my years nice to have one. A bit disappointed not sealed for safety as used my one in the wet never a problem but Clive would not have made a video.

[@johndododoe1411]

If outside is wet or dirty, power can reach finger no matter what's inside.

[@TC_here]

I always found phase testers/Voltage testers like this a strange bit of kit.. Stick this screw driver into the mains and touch the metal bit at the top.. if it lights up you have power :) What could go wrong..

[@wargamingrefugee9065]

And that's why God invented the apprentice.

[@gordonm2821]

I agree, never trust anything where you are part of the circuit

[@plainedgedsaw1694]

I heard about some people testing mains presence by chewing on whole toothpick to make it more conductive and to feel the shaking when they poked the mains with it.

[@muzikman2008]

I used to remove the resistor out of neon testers and wrap a bit of copper wire around its leads to effectively short it out, twist the neon legs together, then put it back in. That stopped the idiots using death trap tester Screwdrivers... 😂☠️.. I didn't really, but should have pmsl. Drop these lcd testers in the sea and watch it glow like its user.. Bin them.

[@plainedgedsaw1694]

@@muzikman2008 those testers have their place, sometimes you don't have second point to measure against. I do have a few stray single wires around my house, that turned out to be live, but there really isn't a point around where i could ground one probe of dmm to find out.

[@whitesapphire5865]

I have a couple of these, somewhere. I've never really been convinced of their worth, but as a quick test of "YES/NO" potential being present, they might be alright, though I think I'd still prefer an active method of testing before putting any fingers at risk. As a rule I use the "Lo-Z" feature on my Fluke.

[@zyeborm]

A positive indication means danger, a negative indication doesn't mean squat lol. I'd still test with the meter then crowbar it just to be sure 🤣

[@jp040759]

WOW. Simple but complicated. Very cool idea. Sure are some smart/creative folks out there.

[@EverBeyondRadio]

"Probably Fairly Safe"...😆

[@Lucius4992]

Interesting. I have had one of those for many years now, no one died yet, also never teared it apart and mostly used it as a small screwdriver for adjustments. It was always weird for me to think that we are supposed to stick our fingers in it while connected to mains and without knowing what's inside. I damaged the lcd by using an igniter just for fun. Thank for the video!

[@Knaeckebrotsaege]

Had one of these in all black when i was a teen 20+ years ago. Difference was mine had actual metal buttons and the whole thing was definitely not openable (I tried.. obviously :D). Definitely neat to find out how these thingies work so many years later

[@curtishoffmann6956]

"It's probably fairly safe." "Here, hold my pint."

[@LarixusSnydes]

This is in fact an Integrated Circuit, but on a macro scale and without using silicon Fascinating to see it seemingly perform switching, but without a single transistor.

[@TATICMOOR]

I used to have one of these many a year ago, it was handy to use the end as a flat terminal screwdriver too.

[@jensschroder8214]

The LCD can be compared to small capacitors, which are also the display.

[@stephenmanning1553]

When I first lived in the outback of Western Australia there were a lot of remote "properties" with local gensets producing 36VAC. there were 36V light globes available in the shops. Sorry I don't remember if there were 36V washing machines, radios or whatever?

[@amorphuc]

Fascinating. Thanks Big Clive.

[@wavemaker54]

It would be cool to know what equipment you use when making these videos. Someone on here probably knows or there’s a previous post with all the info already gathered together. Clive, I appreciate your knowledge and the desire to share and teach what you’ve learned throughout your career. Thank you.

[@tomschmidt381]

Interesting circuit taking advantage of LCD operation. It looks safer then the neon screwdriver I have where you touch the clip to provide enough capacitive coupling to cause the neon indicator to glow.

[@daveschmarder-1950]

This device is self-testing. If the resistors become shorted, there will get an indication of you screaming as you touch the mains.

[@dblitroot]

The common connection in These types of LCDs are driven by AC voltage. The common connection on these types of LCDs is called the "Back-Plane". The segments are capacitively coupled to the Back-plane. To turn the segment ON it has to be driven with the voltage that is 90 deg out of phase to the BP. When in phase with the BP the segment is OFF. I think the voltage is what will destroy an LCD, not the current. Also, they absolutely must be driven by AC voltage. DC voltage will light up a segment, and can be used as quick test, buy it will "burn" it after a short time.

[@twocvbloke]

I've had a few of these in the past, never used them for testing, just as a crap screwdriver, cos I usually made them go crunch either through too much torque or from using them to pry stuff open... :P

[@TheTruthAboutLemmings]

What a nicely minimalist design. I've got one and just assumed it had a chip and button battery in it

[@ianrtait5721]

Excellent explanation. Very informative.

[@Neovo.Geesink]

If you have the Uni-T or another meter which can measure Ohms, You can probe the LCD to check if it will react to that low voltage. If no reaction, try swapping the polarity, but I recon that it Will show the symbols for a brief period untill the crystals will realighn.

[@CanizaM]

Based on the title (and the HUGE TEXT in the thumbnail) I was momentarily confused that this was some sort of special tool for assisting with the repair of LCD monitors and the like. Also noticed the packaging claims it has a "fine display". Not great, not bad, just fine.

[@johncrook4469]

Your videos are truly amazing!

[@richardbriansmith8562]

Awesome Video big clive

[@dcallan812]

Handy bit of kit.. I dont think I would let my mother loose with it but stil luseful.

[@wisher21uk]

Looks cool Clive thanks just hope they’re safe, I always double check with my fluke meter and switch the mains off completely, you may laugh but my friend got a shock as his flat was wired to nextdoors flat ....

[@Kitten-Master]

a remarkably simple device. i may have a few laying around. or at least something similar in external design never actually used it before... always just used a meter

[@joelmurphy9369]

that's a brilliant design. optimize everything and reduce component requirements to zero. Supply chain kerfuffle-proof! Clive, you are so good at giving us a close up view of the things... why, for sooth, won't you show us a close up of the instructions!?!?

[@edgarmatzinger9742]

Looks like a rectal thermometer to me. It would a problem if that thing would report 110v when inserted....

[@German_byte]

I like that if the unit fails you could still use it as a screwdriver.

[@jussikuusela7345]

I got laughed at in vocational school when I told people that everything that is conductive and has a surface area, including humans, has a capacitance, and that is how the neon screwdriver thingy (as well as this) is coupled to ground by the user to complete the circuit... and the reason why you will likely feel a small buzz in your fingers if you accidentally touch a live circuit, even if you are standing on a dry wooden floor wearing wellies and touching nothing else... and why if you touch the radio antenna the reception may be greatly improved in certain circumstances, and why touching the core of an audio input cable will cause a buzz on the speakers. Among other things. Likely many of them still think there's just some obscure magic to how these things work.

[@ernstoud]

Note the large distance between the C and the E in the CE mark. This is a Chinese Export product. For sure not compliant with any safety standard.

[@steadfasttherenowned2460]

When will Big Clive and AvE meet up and bumblefack their way through some fun stuff? Maybe Clive's brother will tag along with a couple bottles of reserve.

[@richkh]

That blue plastic shell has been repurposed from a digital thermometer. Made from the same molds.

[@janami-dharmam]

that is called innovation!!

[@tundramanq]

Bare LCD displays are damaged and eventually destroyed by exposure to sunlight. The whole screen progressively turns black permanently. Make sure the display has a very good UV filter plate on top around UV sources..

[@dantronics1682]

it only cost a quid

[@johns2038]

I might become a patron for these early access videos...

[@bigclivedotcom]

Right now the Patreon feed has a lot of backstage show stuff not released on the main channel.

[@dimitar4y]

@@Okurka. yes, the normal electrical videos, not his actual job with the backstage show stuff, which actually requires him to put more effort and take "time off" the work he does itself. Also 1$ is not a pay wall lol

[@d.t.4523]

@@Okurka. There is not likely any technical disassembly going on backstage. His "videos" are for technical reference, for we techs. Random goings on isn't his normal video, so it's not meant for this venue.I'm not a patron, so don't blame me for defending his choice of content. I like the techie stuff, and don't have time for the random content. Good luck to you. Make me some videos if you like, but don't complain about my preferences. Thanks for your input. 👍

[@dimitar4y]

@@Okurka. oh woowee, 2 dollar, i'm going BROKE. Dead broke! End of the world! :l

[@Mark1024MAK]

@@dimitar4y - if you’ve got some spare cash, send it my way and I will find a good cause for it 😊

[@randycarter2001]

It uses you as an antenna.

[@SaltyPuglord]

And a capacitor as well!

[@Shaun.Stephens]

Merci mon ami.

[@q12x]

It would be good to explain why it is functioning. My impression is that 50Hz in the mains and in my body (as an antenna) will drive each segment of the LCD through its coresponding printed resistor. Each of those numbers are in fact a single segment shaped as a number or shape(the flash).

[@bigclivedotcom]

The LCD requires very low current, but does need a voltage threshold. It's done with a high resistance voltage divider, with you as one of the resistors.

[@q12x]

@@bigclivedotcomhmmm... I believe the complete answer is that the LCD is driven with 3V AC! _sinusoidal_ at 50Hz. From practice I know a LCD segment is working with 3V DC at 100Hz alternating in both the pos and neg rail.Basically an AC but made from a square wave.

[@kevinmartin7760]

How much voltage would it take to arc between the traces to the NCV terminal, bypassing the resistors? Those clearances look pretty small!

[@IanSlothieRolfe]

The seperation for mains voltages (240-400v) reccommended is 4 to 6 mm so I would say the seperation on this gadget is barely adequate, although the resistors would prevent a significant (i.e. dangerous) current flowing. I'd be happier if there where some kind of solder mask or other insulating coating on the board personally, but I think the NCV test is relying on the capacitive coupling between the probe connection and the track (the bit of trace going round the probe connection acts as a capacitor), so they had to run it fairly close.

[@kevinmartin7760]

@@IanSlothieRolfe The only protective resistor would be the one next to the NCV contact, and there is also a narrow gap there potentially bypassing that resistor. The other hand contact is well-isolated by a resistor.

[@deepblueskyshine]

They've cheapen the product, but meawhile they've increased the price. Some 20 years ago when these chinese testers appeared they cost the equivalent of 50cents to a dollar (at least in my country - Bulgaria and were several times cheaper than a neon bulb live wire tester) and worked in a logical way - only the detected level appeared on the LCD display. I guess there were some simple logic COG capable of working from a tiny charge on earlier models, but no more.

[@ruben_balea]

That model showing only the closest voltage was also available in Spain, at least in the Chinese bazaar nearest to my house, they had them for €0.60 while their classic neon screwdriver was €0.99 A genuine Wiha type 255-3 made in Germany was at least €3.50 at hardware stores but there were also clones for half the price.

[@deepblueskyshine]

@@ruben_balea Nowadays in the cheapshop near me there is nothing under a euro.

[@ruben_balea]

@@deepblueskyshine Here Chinese bazaars must be the only ones that have a lot of things for 1 euro or less, mainly because they seem to have thousands of things for sale so they can have a few hundred things for less than 1 euro because those really don't have much value. Then the rest depends, it can be cheap and bad, cheap and acceptable, on rare occasions cheap and quite good... and the same happens with more expensive products. I still bought a pot lid knob for 1 euro a couple of days ago, best quality stainless steel ;-) the steel is actually pretty decent and doesn't rust, but the screw they come with is aluminum and I swapped it out for a stainless steel one. I had already bought those more times, to replace the hard plastic bakelite-style ones when they crack. Then the classic shops "everything for €1" really don't have almost anything at €1 but rather at €2 or 2.50 and in the end they sell practically the same products as the Chinese bazaars.

[@d.t.4523]

Great. Do they make a current clamp version? I should incorporate that into my HV gloves, as a visual indicator. Good luck. 👍

[@Cenentury0941]

1:45 you read the reading incorrectly, bro. You're getting 123.6 gigavolts on your outlets. Should probably get your wiring checked.

[@fortuner123]

The one I bought in Thailand instructed you not to touch both buttons at the same time! I have no idea why but because of that I never use it!

[@davidfalconer8913]

For £1 , this is great value , but I would always use a neon tester for ( UK , 230 Volt ) mains .... the LCD uses the alternating supply as it's protective clock frequency ( normally a 30 hertz square wave in most other pricey equipment ) .... LCD's work also on DC , but prolonged use on DC strips the transparent tin layer off the glass , this will shorten this testers life ... but ... hey it's an excuse to head off down to Poundland™ and buy another ( + lots of other bits ... the little green cable ties are good value , garden shelf , wiring looms don't mind a different colour ( Ha - Ha ) ................

[@albear972]

It looks like they repurposed a common LCD thermometer to make this item.

[@davidbarrass]

Are you doing the Tatoo this year? I was watching some of your work on Saturday from the Simple Minds concert down in Princes St Gardens

[@PeterShipley1]

do you have for the old neon bulb screwdriver testers. I'm sure the younger viewers have never seen one.

[@mintyfreshpenguin]

Probably and fairly, are not two words you want to hear in a sentence with safety.

[@Jimmyfisher121]

That is what I call lawyer print, you know when it is important information when it is a micro dot.

[@eded8045]

i got 2 now as gifts from Ali years back ))

[@RIXRADvidz]

what a fluffy soft comfy bench, are you going to upgrade your bench when you get back to the island? as nice and fluffy comfy as this bench is, it's probably not a good idea for all the burning and shorting that goes on, owell, it was a dream for a moment.

[@joerod7526]

3:57 " one moment please "

[@Dave96z34v2]

Should have made it with a conformal coating to prevent moisture arc over.

[@tncorgi92]

I am curious, how much did that cost? I just had to buy one, at the home improvement store they ran from 10 dollars to about 30, depending on the bells and whistles you want built in.

[@calv6051]

This one is from Poundland in the UK. It costs £1 or £2.

[@tncorgi92]

@@calv6051 that's pretty good, the one I bought doesn't have that kind of LCD display. Just LEDs and a beeper.

[@benespection]

A really interesting design compared with the traditional neon bulb death traps, but I still really hate the idea of testing if a circuit is live by becoming a part of the circuit itself. I think I'll stick with my non-contact volt pen for any quick live/dead verification and smugly enjoy my 1000 V isolation. :)

[@robsmith9392]

Iv an odd question not directly related, I think I have an access point being scrammed by dodgy mains voltage something like transients Without breaking the bank and spending a mass fortune in high end Fluke equipment, have you any idea how I can detect these as I just may be barking up a wrong tree…

[@LawpickingLocksmith]

Amazing!

[@DjResR]

Stalwart brand from Maxima in Estonia has same device._

[@WilliamWallace14051]

36 Volts for golf carts and GE Elec Trak lawn mowers.

[@laernulienlaernulienlaernu8953]

Does the direct test still give you a tingle if you touch an earth while testing mains voltage? ⚡

[@Leahi84]

How are you getting the zoomed photos when you're not at home? Just curious.

[@bigclivedotcom]

I improvised a studio setup and bought a new printer for shared use at work.

[@MsLancer99]

I've brought one of these from Poundland but now I can't find it. It's great fun to use

[@petersage5157]

I'm surprised that the readout has all the ranges smooshed in-line and not rotated like in your reverse engineering diagram. Would be a lot easier to read that way.

[@OneBiOzZ]

I have not seen printed resistors in a very long time

[@andrewsmart2949]

ford tried the screen printed components thing on an ignition module called "thick film ignition",it was terrible,at least you can replace it with a bosch module that works LOL

[@Slikx666]

It looks like a Poundland thermometer but slightly different. 🤔👍

[@phonotical]

Anything that tests if the power is on or not and uses you to pass current through, just no If water got in, could the tracks wear down

[@svenboske844]

Wow, it seems this Things havent changed much in the last 30 or so Years. Except mine has a detachable Clip, and is not so easy to open.

[@Namenloser_]

Oh great the Pen of Death is finally digital.

[@bitelaserkhalif]

Alas, I thought it was a multimeter crammed in small thermometer packaging

[@Oneloudest]

Are you not working the Tattoo this year? Always loved watching the behind the scenes footage.

[@Flying0Dismount]

You completely missed the obvious free gimme on this unit: they repurposed a rectal thermometer casing.. So many missed opportunities for witty but slightly off color dialogue...

[@MRLAW243]

Flip the plastic screen cover and it will invert the colour

[@crazygeorgelincoln]

One could try to make it waterproof to stop the moisture escaping.

[@stephendavis6894]

I bought one of these in 1990 for £1.50 and have used it a lot as a quick check. Went to use it a couple of weeks ago and there it was - gone!

[@dantronics1682]

if you do a direct voltage reading on 12v battery it will start working again

[@stephendavis6894]

@@dantronics1682 I meant that it has vanished, not in any of my toolboxes and certainly not where it should have been. Didn't have my multimeter either but managed to complete the job without burning the house down.

[@frogz]

wheres the micro?? love it lol

[@eak125]

Of course Clive travels with a spudger...

[@g7mks383]

Nice to know that once again we have to put our lives in the hands of the Chinese printed resistor

[@piconano]

Ingeniously cheap device. Looks like a thermometer! They could've made it even cheaper, by eliminating the buttons. Soldering small posts on the pcb pad that poked through matching holes, where the buttons are now.

[@S.park.y]

I wouldn’t ever test anything greater than 12v with these things. I’ve been bitten before, once bitten twice shy

[@chrisw1462]

Hmm.. Metallic buttons on a voltage tester... "Just touch the buttons to find out if there's voltage in the circuit!" Yeah, I bet!.

[@gin3648]

I prefer zebra strip, hope that helps.

[@Derek_Garnham]

nope, it's zebra. why? - because it just sounds better that way.

[@Pulverrostmannen]

Man I would like to test the insulation properties of this pen with my 3KV supply to see how it would react both in LCD and Isolation properties

[@kevinhardisty6465]

Clever in it’s simplicity

[@hughaskew6550]

The resistance values don't seem to correspond to the voltage scale...

[@dougiedrever7168]

more soda stream vids please