Volt stick circuits and tests
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- เผยแพร่เมื่อ 26 ก.ย. 2024
- A look inside a generic Volt Stick clone. I had one of the first Sagab versions with what I think was a metal body, and I recall the circuitry as being similar to this.
They work by amplifying capacitively coupled current with reference to ambient ground (through you).
These units are a handy extra test option for checking if an insulated cable may be live without breaking the insulation. They are not infallible, so all usual safety precautions should be taken.
As with all tools you have to understand how they work and things that can influence their operation. That includes high voltage equipment in the vicinity like neon signs or overhead lines.
They should also be tested before each use on a known live cable.
This video features three circuit variants that can be built with discrete transistors.
While fun to build, it's more practical to buy one for work use, as a significant part of the unit is the case.
If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:-
www.bigclive.co...
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#ElectronicsCreators
Working on the Austin TX Trail of Lights we used these to find dead lamps in series strings as the voltage stops at the dead lamp. When you’re dealing with millions of little lightbulbs it made a big difference.
I've tried to do the same but found it was inconsistent or fails to detect voltage beyond a certain point on a known good string - mine doesn't say the min voltage. Do you know the min voltage on yours?
@@bbaldwin9411 It's not supposed to light up on a known good string; you need a dead bulb to cause a significant voltage differential.
@@CoolerQ if we are measuring the voltage between the wire and ground reference as described, there must be a voltage difference, starting at 120 and decreasing along the lights as they are in series. So the tester should detect voltage all along the string until the string is broken,, or the voltage drops below the testers detection limit. If you are measuring the voltage drop across each light then yes the drop would be small at every light, and large only if there is a break.
@@bbaldwin9411 So would i be able to use one of these to find a break in an extension cord?
@@oodmboo Yes, but it will generally fail at one end or the other, where it is flexed the most. If it broke in the middle replace it, as this shows it was pulled too much and you will have multiple nearly broken places in it. You just power the cord, and test at the start all way round, as the other conductors will shield the line, and then half way down, then at the end. Will show a broken line, and then plug in a lamp, and you can find the broken return. Will however not be able to test the ground conductor is intact.
Back when I was a wandering electrician, we used the crap out of those those things. Or at least the modern versions. Though we called them "wiggys" cause of the siren noise they make. Absolute lifesavers, particularly when you're crawling around up in a ceiling of a building that has a hundred years worth of wiring. Some of it still very much live for a hundred years, even if it isn't actually hooked up to anything. Until it hooks up to you when you bump up against it was hidden behind something with bare copper hanging out, despite locking out the breaker box. You can probably guess how I'm familiar with that. Nothing better than a hot wire to the ass while you're 30+ feet up on a lift. Good, good times.
Ahh yes, the old spider wiring, also familiar with that. These test sticks work wonders for that.
I watched an apprentice trying to test one of these on my Proving Box. He convinced himself that my Proving Box was faulty because his volt stick worked on the cable to the radio.
I told him he was wrong and needed to look at the Proving Box specification and have a think about how his volt stick worked.
Fair play to him, at the end of the day he'd figured out that the Proving Box was a ramping 600 volt DC, that it worked by the meter tip pushing a metal contact down, that his volt stick couldn't reach the shrouded contact and that, since it used an induced current the volt stick wouldn't detect it. The following day I confused him some more by showing that the Proving Box would make my volt stick light (mine has a longer tip and it works with a small Hall Effect IC so it will detect DC voltages).
Biggest misuse of one of these testers I ever saw was an HVAC "technician" (who had his own company; probably still does) use one to determine that an AC compressor in an outdoor condensing unit had failed. He used it to check for voltage at the compressor and it showed voltage at the compressor. Only one little problem--that condensing unit was equipped with a contactor that only opened ONE of the TWO 120V-to-ground legs (this on USA split-phase power). So the voltage tester was correctly showing the presence of voltage on the compressor. It was, however, NOT showing a complete circuit. They aren't designed to do that. It also didn't occur to this dipstick to wonder why the fan in the condensing unit was also not working. Since I was asked to look at the unit by a friend (I am NOT an HVAC tech) I noticed that the contactor didn't seem to be pulled all the way in, and I checked the voltage across the output with a multimeter, 0V. Then I took one of the probes and pushed down on the contactor and the guts of a dead bug that gotten into it squished out as both the fan and compressor turned on. There was NOTHING wrong with that unit other than the bug in the contactor, although I probably would have replaced the contactor if it were my unit, maybe with one that has a little better protection against bugs getting inside.
@Brian Leeper - debugging, in the truest sense (and if I remember this right, the original sense).
@@matambale You remember correctly
Yes I have seen those cheap contactors, and generally regard them as replace on sight with the sealed 2 pole version, as they do work better, and are less likely to fail from dirt and dust, let along moths.
I had the same problem with the paper feeder in a printer once. It was obstructed by a piece of licorice.
Putting a DMM set to Volts across the contacts of a switch, contactor, relay etc. when the equipment is powered up will give you a rough idea of the contact resistance, depending on the load of course. If you see mV's it's suspect, again, depending on the load. If you are into 100's of mV or Volts you have serious problems.
"I thought; what if I cascaded the Darlingtons" This is now my new favourite phrase.
I remember my dad having experienced something like this, and he was amazed at how you just waved it over wires and it lit up like the hand scanner of a Tricorder in Star Trek, he's easily amused... :P
The first kit I ever built (around 1987) was the Maplin live wire detector. It had an LED as well as a piezo buzzer, so you could hear the 50Hz buzz of the mains, if triggered by static it would emit a tone
I had one of these nearly drive me insane a dozen years ago. I was cleaning up some bad wiring in the attic of my newly purchased home. Also adding some flood lights. There was a dead circuit from where they'd pulled out dedicated sockets for space heaters now replaced with a central heat pump. I traced the wire, tested the endpoint in the blanked outlet box. Before the cut, I used the voltage tester as a last confirmation but it was random whether it would go off or not. I'm in a hot attic and very annoyed. I finally carefully cut back the sheathing and pierced the wires to test for voltage and their was none. In the end, I realized my problem had been that I was using a CFL bulb in the work light, that was hanging just above and behind me as I sat on the ceiling joist, so about 4-5 ft from the wire. If I tested while I shadowed the wire, no beep. But if I tested without my body blocking the CFL bulb, beeping.
Really useful for adding a logic level monitor to a mains circuit, without making a physical contact to the live wires. I used one to monitor a PIR controlled outside light.
To make a voltless main monitor switch, it is necessary to add to the circuit show in this video, a Schmitt trigger gate and hum filter, or a retriggerable monostable to remove the mains hum, thus stopping the switch chattering at 50Hz. The gate output can then be used to drive a relay or an opto coupler.
Useful if you want to add a mains monitor alarm to some mains powered device.
I've been in industrial maintenance for over 35 years and have carried one of these the whole time. The only time I don't have one on me is when I'm in the shower or the bed.
These things have saved me hella trouble over the years, and in my experience, they typically lean toward the 'false positive' than the false negative side of the scale.
That's fine. If I have killed power to a panel I am working on but my volt stick tells me that there is a chance that I might have missed some foreign power source, I pull out the meter and probe around for it. Sometimes the volt stick will pick up residual induced voltage on an otherwise dead wire that happens to be running along the same conduit or path with a currently live wire.
In that case, there is definitely some kind voltage present, albeit maybe nothing to worry about as far as safety is concerned. In all cases like that, I get out my trusty Fluke before I sting my fingers in there.
I started out with the Santronics volt pen and stuck with that until they just completely disappeared off the market. Now I just get whatever I can that seems to be made well. I always test any new volt pen I get on known live and dead circuits so I can get an idea of where the false positive / false negative curve lays.
I have one for old Christmas lights, amazing time saver for dead bulbs
I use one of these almost everyday as an electrician. I understand why they work but not how. Loved watching you break it down. Wish I knew more about electronics. It's fascinating.
Take apart a klein!
Initially, I had forgotten this from the Patreon version, but the circuit diagrams brought it all back.
I remember seeing those for the first time while I worked at an electronics parts distributor. They were made by Santronics. I think they were in South Carolina, USA. They sold for around $18 USD as I recall. They also had a low voltage DC model and one more. Then the imported devices showed up and that was the end of those. I loved giving demos. I would show the above ground and grounded wire differences in a lamp cord. Thanks for the ride down memory lane, Clive.
over 30 years ago i worked in the demolition business and had a lot of serious incidents caused by electricians telling us the power was disconnected then finding out it wasnt. i was forever hassling the boss to get a volt stick. they werent cheap then. one day we were totally stripping out the entire floor of a high-rise office building when an orange thing fell when the ceiling panels came down. it had been up there for a long time judging by the dust on it. it was called ezscan. ive still got it. i didnt tell the boss till 25 years later. its got 6 leds. the closer you are to the action the more leds light up. ive never seen another one. nor have any of my sparkie friends.
My Fieldpiece clamp meter has a similar circuit built into the clamp tip. They are quite helpful. Thank you for hi-lighting them! 👍
Your soldering of component legs together is the kind of minimal solder, neat job, what I wish I could do when I grow up.
I'm 40.
I love this channel ❤️
I remember buying my first one of these style ‘testers’ in 1989.
I was a ‘day shift maintenance electrician’ assigned to work with 2 contractors on a big installation. I spent a year working with these contractors and I have to say they earned their corn!
I wasn’t quite 30 years old and here I was showing off my ‘magic wand’.
Not one electrician said they’d trust it because if the battery failed your test failed.
There’s a place for non contact testing in fault finding but I would not rely on this alone.
I use a similar type of tester for checking solenoid coils are energised. I could use a ‘terminal driver’ on the coil and feel for it being pulled down but ‘fitters’ are impressed by a pen that lights up.
Providing you test immediately before use on a known energised line these little devices are both reliable (VERY reliable) and safe. As far as "the battery failing" - a) this is why you test first, and b) zinc carbon / alkaline batteries do not "suddenly stop working", so that's a red herring. The current demand of these devices is so very low that even nominally exhausted cells will still "work" enough to allow some detection capability!
@@phils4634 The fact I embraced this technology 30yrs ago and still have one in my tool box means I’m comfortable with them.
That is incredibly simple and demonstrates how much I need to learn just about simple circuits!!
A Beginners set of videos would be very helpful to someone like me who can take things to bits, test obvious possible causes of non functioning items and when successful replace but I don't know exactly what half the things do and why they are linked in certain ways! I continue to learn from all your videos, thank you very much.
I think I can cope with this circuit too :)
I know Clive has a video titled something like "basic electronic components" or something like that, might be a good place to start if you haven't come across it already
@@JordyValentine First, outstanding AF handle (if you can prove it.)
Second, yes. I recall watching that video many moons ago. Your comment reminded me that Dave (that EEV blogger from the upside-down land where all the elections fall out) has a series which makes for an excellent first and second year course on the basics of all these squiggly drawings.
What really throws me for a loop but its probably a very simple thing for electricians is wiring lights to multiple switches. I know its probably simple but until I do it and understand it with my own hands I can't think about it, even when trying to follow one of CliveCAD's diagrams.
@@MrShwaggins Think of it as using two parallel wires between switches feeding the end light switch that supplies the light. The switches in-between cross the feed over from one side to the other, so the final two-way switch is only energized on one connection and depending on which way this is flipped decides if the light is on or off. If one of the intermediate switches is flipped the supply goes down the other leg and the light is energised.
These are pretty cool, the clamp meters have the ncv which does the same thing.
Hope you're feeling better Clive...
The heart palpitations still come and go with me, some days I'll be fine for a week, others it's every hour of everyday....
Best wishes.
It's 3am, I had to watch this with the sound off but still brilliant. I have gone through many of these things in my time, they aren't very drop proof I found and I always seemed to go through batteries.
I also have, or had because I haven't seen it recently, a magnetic detection stick for solenoid heads, that was a great little gadget, looked just the same 👍👍👍
I worked for Santronics/Static Control Components for a couple of years. It was a small town operation. We made them for all the big names at the time.
Small world. Someone else from Sanford.
@@randyhardee4773 did you know the Schwartzes? I only worked there as an engineer for 2 years. Learned a lot made some cool stuff.
I didn't but several of their people went to BCA (where I work) when Static closed.
While renovating an old house it was my job to exterminate the old wiring wherever some random old wires showed up in walls and floors. So I made myself a life-saving working glove with an antenna fixed with some sticky tapes around my fingers. Whenever I grabbed a live wire, an LED on my glove lit up and I was at least warned. Saved my butt several times I guess..
This brought back the memories of my old job. They were telling the story of a technician who moved onto work for another branch of the company by the time I joined.
Rumor has it, he wanted to check if a connection was live, he didn’t know it was high voltage, he didn’t use the HV NCV testing probe, he went ahead with the classic flat head screwdriver/test-pen instead. He was shocked but he survived. His anecdote was that test pen was glowing even before touching the contact. He unwittingly invented NCV.
yeah i've done that with a neon before on crt leads from a tube i was sure was discharged. it wasn't
My earliest ones were definitely FET input (with a bipolar transistor follower). Resonably reliable, amazingly durable, and providing commonsense is used a convenient method of detection of a "mains presence". The "mains detector" elements in many current pocket meters (such as the BSide ADM51A) use an "all in one" chip that drives the meter and provides a (graded) response, which is a useful feature when playing "hunt the cable" behind timber or Gyproc panels! :-)
It is my "No Dying Stick" and it has come in handy MANY times!
The transistor in my Fluke tester is an FET making the input impedance quite high and more sensitive.
I used it in the loft to locate a feed wire to the upstairs lighting. There’s no way I could have identified it without this stick, so useful but only for certain issues. After locating the wire, isolated the circuit, proved dead, then extended.
gosh glad I still have you tinkle my bell when you post a vid.
I missed this on 2 weeks ago!.
Very handy bit of kit, BUT dont rely on it alone. 👍👍
Using the first stage as a preamp makes sense. It not only allows for the antenna and input impedance to be set, but it removes the 3x 0.6V offset on the antenna side that one would have with that many cascaded transistors.
The shirt swipe test is a great trick! I didn't know that one, but it's obvious in retrospect. The best tricks always are. Thanks for sharing it, I've always been able to find a 120v line to test with, but that saves steps.
I was surprised not to see a FET in there. The related circuit I know about is the electrostatic field detector (sounds like the ghost detector), which uses a common FET with a leg bent up as the antenna. You should revisit the ghost detector, it's a fun circuit and I think I vaguely remember it on here years ago. If it's one like the circuit I found, they're easy to make and fun to mess around with. Though the FETs aren't nearly as common for new folks to have (everybody has an excess of NPNs).
They're cute, too: they fit on top of a 9v, waving hello at people, while blinking like something Tom Baker would've had to disarm before an evil green bubblewrap monster blew up some planet or another.
I've avoided FETs in my electrostatic charge detectors as the floating input is very easy to damage with electrostatic discharge. It really needs some form of protection.
You should know that there are models of volt pens / sticks out there that have options for variable sensitivity, and when the sensitivity is set too low, the "rubbing along the shirt sleeve" trick doesn't work so well.
I have one that can detect a rub on a shirt sleeve every time on the highest setting, about 30-40% of the time on the middle setting, and never on the lowest setting.
There are uses for the variable sensitivity capability in some circumstances, so I'm not angry about it being a thing.
@@jdgower1 Mine works on my hairy arm lol.
Straight swapping in a small JFET for the frontend would increase sensitivity, while a MOSFET might perform better in the negative feedback configuration... pulling it off with three of the same transistor is highly economical though!
I really expected a single-MOSFET circuit when this video began.
Using a JFET or any FET in this circuit has the problem of being damaged by static discharge. The three BJTs are much more resistant to damage.
@@acmefixer1 Especially since my favorite way to test mine before use is to rub it on my pants until it goes off from the static.
By putting the 3 Mohm on the emitter of the 1st transistor instead of the base, it's effect on the input impedance is multiplied by the beta of the 1st transistor. ie: If the beta was 100, then the 3 Mohm resistor on the emitter to ground would be the equivalent of putting a 300 Mohm resistor on the base to ground.
Yep, classic emitter-follower circuit.
I have such little knowledge of electronics but I love and am fascinated by all your content Clive!
Thanks for the interesting video. I have a volt stick like that, made entirely of aluminum, except for the sensor tip, of course. I bought it about 30 years ago. Because I rarely use it, I never leave the batteries in. Such a non-contact phase tester is ideal if you have to look for a blown fuse, or a broken cable, or to plug in lamps with the correct polarity. I always check uninsulated contacts or wires with a simple neon glow lamp phase tester, which is a bit safer than with an electronic one, and the screwdriver is built in at the same time.
Simple circuit. Clear explanations. experimental models..ect.. This is why i enjoy watching you videos on electronics. photos, diagrams and time put in to all your work to...doing what you do best. Peace DVD:)
Such a simple yet effective design! Might have to be the next weekend project! I'm almost tempted to crack open my Klein stick but in the name of safety I must resist.
But, resistance is futile!
@@whitesapphire5865 and measured in ohms
In the past, long long time ago, I repaired blood pressure devices, the pickup device in the arm piece worked in the same way.
It was fit in a little round metal case around the size if a 2 euro coin, and functioned as an antenna to pick up the blood flow in the vain.
I really enjoy your tear down videos and it's been fun seeing my understanding of these designs increase (not linearly) as my time in college continues.
I remember when out carpet cleaner stopped working at work one of the maintance guys used one on these to check power was getting where it needed to, what that didn't take in to account was the neutral had become disconnected and that was the actual fault.
I like these, my meter has one built in, I mean I never seem to use it, but I like that it's there
My volt stick has come in handy so many times !
I must be learning something, because as soon as you said "Volt Stick", I'm thinking Darlington Pair.
Now, about 15 years ago we had a couple of small screwdrivers with a flickery LED in the handle. It ran on a pair of LR44 cells. I used to call them electronic rats because they detected live wires. I'm not sure I'd want to put too much trust in them, but they were a novelty at the time. Nowadays, we have a Fluke 117 DMM which incorporates a voltage detector, with I think, the intended purpose of allowing you to avoid drilling into live cables embedded in walls etc. It's also good for finding breaks in extension leads and suchlike. Even with a name like Fluke, I'm still not sure I'd trust it 100%, especially since it sometimes detects copper pipes as well - and they're not live!
They're not *supposed* to be live.
But we all know stupid happens.
You might actually have some capacitive or inductive coupling into that pipe.
I built one of these from a free kit from Maplin back in the early '80s. I think the strip board and components were on the cover of the Maplin magazine. Of course you wanted a case to put it in and these were readily for sale at Maplin! :-)
Clive with the live wire just laying on the desk while taking the etester to bits and the doodling section of the video 🤣🤣🤣
Looking forward to your post about the fire effect feature.
Those in continental Europe should check that the tester has a round tip like that one. There are many testers with flat tips on sale. They are made for the US. They may give a false negative result on an European socket that is live.
Some years back I fiddled with designing a version that didn't need batteries- a FULL BRIDGE RECTIFIER made of Schottky diodes (or tunnel diodes but I couldn't get my hands on any) and a low-current LED, but got distracted with my actual job. These days my old eyes won't let me do most soldering tasks.
I won't be offended if you give it a shot. ;>)
Big Clive,
Great Video but an experienced Electrican once told me that a Volt stick only shows where Voltage is not present and NOT where it is present.
The unit I have has what I assume is a potentiometer in place of (or probably in series with) the resistor, so I can adjust the sensitivity. The other end of the unit has the ability to detect current.
I think you may have it the wrong way round: I'm fairly sure the way the last two transistors are configured in the existing product is the classic way to do a darlington array. I agree, though, that the forward voltage drop is lower if you attach the collector of the first transistor of the array (of the last two) to the positive supply rail. Generally this would necessitate an extra resistor in series with that transistor because otherwise it could conduct too much current from VCC straight to GND if it got turned on hard enough, and damage itself. In this particular application I don't see that happening (the LED doesn't have a resistor either), as the input signal is very weak.
I wonder if anyone has ever thought about putting one of these into a cordless drill
I agree... Darlingtons always have their collectors connected together.
There have been drills with these in them, but by the time the drill bit is close enough to the wire to make it show voltage you probably are only a turn or two of the drill away from being through the insulation and into the wire anyway.
I think Clive was considering the difference between
Darlington - > transistor
Transistor - > darlington
Not that there wasn't a darlington somewhere.
Reading some of the replies the last place you'd want one of these is in a power drill of any type! 😂
Exactly.
These are are brilliant. Yes you should and must always double check with your meter. But when you have a control cabinet full of what should be totally ELV these things are quick to run over every cable and occasionally, just occasionally you find mains voltages on something where it has no right to be. These are also valuable in roof spaces - cut wires - ungrounded metal flashing - pipes. Its worth running the stick over these things before you go anywhere near them.
Clive:
About the circuit of your tear-down: If the 'antenna' of the voltage stick uses capacitive coupling... the very small capacitance (between the electrified conductor, and that antenna) has a very high impedance, at 50/60 Hz. The high value resistor/resistance in the emitter of the first transistor is multiplied by the transistor's beta... so that the transistor's base impedance is very high... and so the transistor's input impedance 'matches' the 'antenna's' high impedance. AFAICT, the 'pull down' Darlington pair is just driving the LED...providing enough current to ensure the LED is bright enough. It's a bit naughty (as you say)... because the only current limit is the transistor pair (no limiting resistor). But, it's probably okay because the LED is being pulsed... and these voltage sticks are very inexpensive.
There are a number of patents for 'voltage sticks'... including a patent from Fluke (for mounting a voltage stick on a DMM probe... which seems inane.) Another has a voltage converter so that the voltage stick can be powered from a single 1.5 V cell. Most of these patented voltage sticks are using a CMOS Schmitt inverter, for this logic family's high impedance inputs. Most patented designs also have/use signal conditioning. Which leads me to speculate, the simple design in the tear,down should respond to sufficiently strong signals in the LF,HF, and up frequency bands? ... perhaps limited by the fT of the input transistor?
Cheers.
I could never bring myself to trust these things and still test with a multimeter. Something from the past I remember was a tester with a neon lamp that looked for ground through the user holding onto a metal clip on the device. It looked like a screwdriver with a clear handle that contained the neon bulb and resistor with a metal pocket clip.
Had one when I was kid. Thought it was neat.
Those are useful if you ever find a single wire and want to test if it's live while there's nothing grounded around. Or use it as screwdriver that tells u that you were overconfident in thinking you turned off the right breaker.
Nice, I built something similar with a pink led and a diode to indicate the moment before lightning strikes.
A few years ago I bought one of these made by Klein, it didn't tell you the actual voltage of course, but it did have 2 indicators, one for 120 V, and one for 240.....that was handy to know, since I was Electrical/Mech maintenance guy, lots of motors....I had 120, 240 and 480 all in the same conduits and J-boxes. Most of the 240 and 480 was 3-phase...that can be...shocking...! There's a good reason you keep one hand in you pocket...
I've never had to hold onto mine. You can actually wedge the tip into a socket and hear it's buzzer (if they have one) while you go to the switchboard/service panel to find the circuit
I've got a multimeter with this feature. The antenna is in the top of the meter, and it lights up the indicator on the top with the strength of the signal. Green for weak, red for strong, with an "L" or "H" or "----" on the screen.
Thanks Clive.
I use these for tracing faults on ignition systems, kinda handy.
Awesome video! Love smaller, harder to find, topics like this!
They used to make these with a neon bulb inside. The tip was a metal part inside an insulating cone. The other end of the NE-2 went to a metal part that ran the length of the thing inside the tube.. Your hand had to be around that part for it to work.
I mind they were totally illegal to use at the power station where I worked. I never did trust them...but good to know how they worked, so job done!
I have 2 of these non contact voltage detectors, an ANENG VD-901 labeled as AC 12V/1000V and 48V/1000V (Dual sensitivity range),
and a generic one labeled AC 90-1000V. These detectors can also detect DC and as low as 5V, as long as the power supply is a switching power supply.
These detectors react to the "switching noise" that the 5V output carry. It will not work with a linear bench powersupply.
With a universal smartphone charger with USB port as output, you can make a simple PCB track tracer as follows :
take a (old) USB cable (from a printer etc....) and cutt of the connector that goes into the printer. Strip the outer layer of the cutoff end, and extent the 5V positive wire with a short cable with a crocodile clip. The remaining 5V negative and the 2 data wires or not needed and must be isolated so that they cannot touch eachother.
Now plug the usb cable in the smartphone charger and connect the crocodile clip (5V +) to the suspected wire and use the non contact voltage detector to detect where the wire is internally broken.
You can also connect the crocodile clip to a PCB trace on any circuit, and use the non contact voltage detector to track the trace on the board.
Because these detectors react to the "switching noise" of the adapter, the negative wire is not needed, and this technique can safely be used on most circuits.
Those last two transistors /are/ in darlington configuration. If you consider a self-contained "darlington transistor" it only presents one base, one emitter, one collector. The collectors inside are attached together. If you were to use one of those, to drive an LED in common-emitter arrangement, you would come up with this exact circuit.
I bought a similar thing years ago the has an LCD display showing the detected voltage, it is also a terminal screwdriver and was just over £1 No batteries,
Bought a 'volt pen' for my son a couple of weeks ago that didn't work.
No instructions with it so looked it up on TH-cam to find that like yours it needed 2 AAA batteries. Works now but I prefer the original batteryless version.
I used to build these detectors out of 4017 counters. I don't know where I first saw the schematic but I was expecting to see it mentioned here! The Mosfet input stage is quite sensitive to the capacitive field, plus, it acts as a frequency divider for a more slowly blinking LED.
A number of years ago when I was doing a nontrivial amount of cabling work (both telephone and network), I bought a "toner", which has two parts, one of which is connected to the wire in question and the other of which is used to find it. That second bit performs this function quite adequately, and makes noise if there's any line power going on. I see no need to get a gadget with a light for the same purpose. :-)
A lot of these that I see in America are binary in their signaling -- either a "yes" or "no". But my multimeter is analog in both its sound and light output, which is really nice for figuring out which individual wire in a group is the live one. Honestly I wish that was more common, though I understand why it's not. Also a funny side effect is that it seems to "sense" a small amount of current both when it's physically jostled, and when it's held physically against a wall, even a plasterboard one with no potential. I've always wondered why that is...
I have seen some made with CMOS NAND gates, linking inputs of one gate to make an inverting buffer, then use another as booster to drive Led and buzzer
I find it hard to trust these things. I don't have a voltstick but I do have a couple of DVMs with the feature. Maybe it's just because I haven't learned to trust them, but it feels as though there are so many reasons why they may not show a result that it's hard to believe they will give a proper warning. Clive's experience with the battery in this one, and the simplicity (and lack of precision) in the circuitry only strengthens my prejudice. I still prefer the old neon screwdriver. There's less to go wrong, though they still have the disadvantage of indicating safety by being 'off'. I guess what I really want is something that reads the actual voltage gradient.
Yep, never trusted them. When you work on control panels and distribution boards these volt sticks light up before you've even got it near. Like you, I still prefer a neon screwdriver for initial fault finding, and yes I test it against a known live before fault finding.I've got DVMs with it built it and don't use at all. Anything more than initial fault finding is done with a DVM at all times. I've caught my staff out when they've been carrying out maintenance on duel supply machines before and they've used volt sticks. Didn't like it when I used a neon to show that there was still mains on the panel, liked it even less when they all had retraining on LOTO forced on them all. Seems they "forgot" that the duel supply machines , apart from two 3 phase 400volt , also had a 110volt control signal wiring from the master control panels.
My view is that I hate the paperwork and funerals, plus I look awful in black ! Test, test and test again, you're a long time dead otherwise.
Simple design compared to the one I bought. Mine is audible and pulses the LED in the same way it pulses the piezo buzzer at a few hertz. It requires you to hold it as the power switch is momentary. It does a self test at power up by pulsing the LED and buzzer once. Power supply is from a boost converter as it only takes one AAA cell. As far as sensitivity is concerned, it will work perpendicular to a cable with both live and neutral side by side at 120 volts and will also pick up the leakage of the interference suppression cap on switching supplies.
It's funny that you're talking about this now because I just built one of these going by a TH-cam video. Actually the first electronic device I've ever built from scratch. It's just 3 bc547 no resistor. It works well for 110v.
Long ago i saw a design that used a cmos divider chip with the clock input as the sense line. The parts list was 9v battery+clip, cmos chip, led, led drop resistor
I made a design from a magazine back in the 80s that used CMOS NAND gates iirc.
I used one of these chicken testers and it turned out that all my chickens were in fact turkeys. It was then I realised you could also use it to detect voltages :)
Nearly bought one today to just find out how it worked 🤣 you saved me £6
The circuit remind me about one of your old project 'The Ghost Detector ' which had a similar circuit and three transistor and antenna which is almost similar. It was the first video seen by me in your channel years ago
I bought one of those back in the 90's from Home Depot. It chirps and lights upon detection. Till now, I never knew how it worked, and wondered how it still works today, even though I never changed the original batteries.
The circuit as drawn is a darlington pair. Tying the collector of Q2 to the power rail forms a cascaded amp.
Puts me in mind of the TV Aerial Ghost Detector.
It's actually an improvement on that with the gain adjustment on the second stage.
i've used one at home to quickly diagnose if an outlet was not working or the device, slap it out and slap it into an outlet.(i am not an electrician) and then i have a cheap multimeter to check closer whats up.
I once called service guys for my rented apartment, and said rooflamp didnt work but all other outlets worked fine, and the bulb was fine(currently using a LED filament type, pretty but quite low light as its the only main source of light). They said i needed to make sure there was an issue and not broken cables, so i used the pen first to check cable going to lamp, nothing came there, then with multimeter checking the connection of lamp to roof, no electricity there. CAlled the guys again and reported my findings, they came and checked it out, found that the apartment above me had renovations going on, had managed to sever the cable going form fusebox to my rooflamp, that was amusing(old style, two solid copper wired, replaced with proper looking cable). i was quite lucky nothing else went kaboom
That's very interesting .. a simple design.. I have a faulty one with the added audible tone.. it lights and beeps continuously as soon as you put the batterys in... looking at this layout I'm assuming now that it must be a transistor shorting out... I will have to disassemble and check it out....many thanks
Very handy tool just be aware of it's limitations.
I bought one of these 25 years ago and i remember it going off standing on the platform waiting for a train. It made a slightly different noise since power for trains is 16.6Hz AC afair.
Worth noting you could also use three PNP transistors -- just reverse the batteries and the diode so as to keep the arrows all still pointing in the right direction .....
Depending what kind of material your shirt is made of, and hence whether it produces a positive or negative charge, I would expect rubbing the VoltStick on some materials only to give a glow when you stop at the end of a stroke and others to glow in mid-stroke ..... The inverting first stage should also affect this.
More of these please.
Great video Clive, I was wondering if you could use a voltage divider on the input stage to pre-bias the transistor to be very close to "ON". I also wonder the effect this would have on flicker, but then again it would probably still flicker the same way.
The problem with your favoured circuit is that there is nothing to limit the current through the 2nd transistor other than the be diode "resistance" of the 3rd transistor. In the shop circuit the LED limits T2 and T3 current.
I totally misread the thumbnail and was extremely curious about the types of events and attractions that I was about to experience at the Volt Stick Circus.
I think Clive's Volt Stick Circus videos are only available on a very select patreon tier.
Wow this is a perfect circuit to build with young students just learning about soldering and electronics! Will it work with the 3v coin cell batteries as well?
Yes will work with them.
I don't know about that detector, but the Fluke detector I have is picking up the electric field, and I don't see how an antenna like that is necessarily going to do the same thing. It's sensitive enough that rubbing it on plastic will generate enough voltage to activate it.
Usually spiral antennas are picking up the changes in the magnetic (B) field, not the electric field (E). If that's true on this thing, then it's going to be very sensitive to how much current is going through the wire under test.
That emitter resistor effectively gets multiplied by the beta of the input transistor, so it winds up being something like 300MΩ as seen by the antenna.
I was going to mention the «Ghost Detector» you built and showcased previously, but you mentioned it yourself.
GR8 4 finding a blown fuse
In an unlabelled consumer;... distribution board...
Always test on a known supply before & after use.
Get to know it's limitation...
Always DOUBLE check your finding...
REMEMBER...
Electricity can bite if U get it wrong...
The 2nd & 3rd transistors form a discrete Darlington transistor. Its Hfe is the product of the Hfe of each individual transistor.
Made one out of cmos inverters with a 10meg feedback...way back in the day
I have on of these it also beeps and is an LED flashlight. so easy to identify live sockets and cables.
Back in the 80-90´s i was developing them.
Bigclive! I just stumbled across a auto darkening welding glasses, I think it's a good idea for a video.
Anyone knows when those first came to market? I'm almost sure I only saw my first one in the last 20 years but they must have existed for longer with such a simple design. I'm kind of amazed I never encountered the schematic for one in a magazine back when I bought them. I'd say they were worried about safety but then I remember some of the projects they would publish back then.
The one I have now is at least 20 years old. It was from Sears. I use it so seldom that I think I've only changed the batteries once.
I saw them advertised in the 1980's magazines, plus DIY versions from then, but the design has been around since the 1960's where it was generally used to detect energised power lines, so service crews could find out at night if a power line was energised or not during repairs.
@@SeanBZA if they were marketed toward tradesmen they probably cost $50 apiece
@@tncorgi92 No, marketed to utility companies, so $500 each for the detector head, and another $1000 for the special pole, plus of course an annual service required as well, with sealed batteries in them, that needed changing at that service as well.
Bought my first one from Tandy (Five Ways superstore in Birmingham) around 1983 - 4. I remember a few designs for "contactless voltage detectors" in Practical Electronics, and a rather complex design (using latching logic) in Electronics Today International - around the early 1980's.
In the mines 1980 (I think this is where these devices originated but could be wrong !) we called them DLI’s .. dead line indicators….. they were blue bodied with a red led at the other end . I wish I still had one for you to dismantle Big C !