Using Kelvin's strategy, the current is supplied and measured using I+ and I- leads and the voltage is sensed using separate V+ and V- leads. The voltmeter has high internal resistance so very little current flows in the sense leads and the voltage across the sense leads, V=(0)r, approaches zero... the voltmeter measures the voltage actually across the DUT. The current leads do develop an additional voltage, V=Ir, but this is NOT the voltage used to compute the device's resistance, R=(V+ -- V-)/I. As long as the sense leads are connected directly to the test resistance, R is rather exactly equal to that resistance. If you must do even better, you can add a guard shell around the current leads to eliminate leakage current and you can compensate for sense lead resistance by applying the voltage divider to the lead resistance and the voltmeter's resistance.
I was very confused from the explanation in the video, because I was certain that this was simply a 4-wire measuring setup, which it is. It's not about canceling the resistance offset, which would be very easy with an offset pot. It's about having one pair of wire for the current itself, and a second wire pair to sense the actual voltage drop, however drawing as little current as possible to cause no voltage drop over the wires itself. I think the video is actually quite misleading.
@@graealex For those of us who would have a use for this device the video makes perfect sense. The device passes current across the test points. A separate DVM measures the voltage drop across those two points. For every 1 miliohm resistance across the two test points causes a 1 milivolt voltage potential [difference] across those two test points. [1Mv = .001volt] [1Mohm = .001ohm]
@@DrHarryT The problem is that Michael gave a completely different (and unfortunately wrong) explanation to how it works. Maybe watch the video again. Your explanation on how it is supposed to work is absolutely fine. One component is generating a constant current (a constant current source, easily implemented with a const current driver), and a second component (DMM voltage measurement) is measuring the voltage drop.
Thank you mr Dranfield for all your hard work getting these videos out there for us to enjoy and learn.Your wealth of knowledge and experience is invaluable.
I want to thank you again Michael for alerting me to this circuit (and thanks to Alan Wilcox for the original design!). I have now constructed my own unit. I already had a suitable enclosure and the majority of components, so the whole thing cost me about £28 (kelvin leads & panel meter accounting for £21). I am truly astonished by the accuracy! I've powered it with 3 x 18650 batteries (including separate supply for the meter) and included recharging sockets.
nice one , and about 20 times cheaper than buying one , as you say incredibly accurate, I had a complaint from a viewer that I made no reference to the original author of the project and I did this because I have a feeling Alan is no longer with us but I cant be 100 percent sure so I thought it was better to say nothing .
Same here and I'm not that far behind you at nearly 58. if you have watched the video where I can pick out a single diode from 3 in paralleled you will have realized just how useful this is .
@@michaeldranfield7140 That video and one video about finding a short on tv screen with those CML 10 uF capacitors, I used to take them one by one until the short disapears, this instrument saves a lot of time. With it and my old scopemeter PM97 by now the two most usefull instruments!
Thank you for taking the time to provide the details and background info on this. I am definitely going to build one and will follow much of the layout you did, perhaps with some minor changes but mains powered and an LED panel meter will be part of my unit.
World Radio History is a fantastic resource, I’ve been using it for some time. Considering it’s an American site, he has managed to scan an amazing number of British magazines and books. Thanks for a very useful video and especially for the advice about avoiding fake components!
Oh man, how complicated is that! It's just a constant current source and the good old LM317T precision regulator with just a resistor and just about any power supply found in the junk box would have done the same job. But I have to say: he did it very neatly and beautifully! A real gem of DIY!
Thanks Michael for the great video and very helpful instructions. I made one, works great. As yours, mine uses a small spare mains transformer with 2 secondary windings. This is very important as you mention because most digital displays use a common ground with the measurement circuit and supply. My meter is 12V supply but I see others using 5V or similar. A 7806 regulator gives a nice stable supply for the measuring part as per the schematic. The kelvin probes are readily available so all in all a great addition to the test bench, thanks again.
I watched your video with great interest, where you found a SMD Capacitor shorted-out on that TV Time Control Circuit. You used your milliohm meter in order to pinpoint the short! I had never realised that you could do this. I have always removed many transistors, capacitors to check if the current flow had gone down in the circuit. Also, I have used cooling & heating various items on the PCB - to effect change (hopefully). Short circuits aren't real easy to locate, well, not for me anyway. Thanks for your contribution in teaching those that are well-under your level of knowledge! Greetings from Sydney.
Yeah, I was going to say the same thing - apply power from a bench supply, but below the usual rail voltage of the shorted rail so things don't actually turn on. Use 1V, and give it lots of current - the offending component will soon identify itself by melting, lighting on fire, or having your finger print permanently burned into it as you hunt around the board for what gets hot
@@andywebber8749 Hi Andy, you need to look for: "Flat screen TV, a very common fault to look out for". I currently have a 42" LG LCD TV with the right side of the screen with just vertical coloured lines. I have already changed the Main Board, and replaced the T-Con. Nothing changed. I don't have a milliohmeter, but (taking Michael Dransfield's lead), I will definitely remove the top section of this TV, (after the T-Con Board) to reveal the ribbon that carries these SMD Capacitors, and simply change-out the whole lot. I really wish that Michael lived next door to me!! greetings from Australia.
Thanks for sharing with us such as good information in general not only with this one. I hate watching a lot of industrial components been throwing away becouse a one small components which cost not even £0.2 stopping working equipment worth a thousands of pounds.
You can also find a self-designed from-scratch milliohmmeter from another great british electronics youtuber, Scullcom Hobby Electronics (video #31 and #43). I appreciate seeing your own design and it's source. That that website is preserving all those magazines digitally (for free!) is a great resource. I bet there are some really neat simple hobby designs scattered throughout the 1000s of pages of magazines you could peruse there. I'm pretty sure it doesn't matter if you connect the voltmeter's ground to the current sink's ground, as long as the voltmeter is doing a proper differential voltage measurement on its +/- wires. Completely isolating it probably doesn't hurt with stability though. Funny seeing a lot of comments exclaiming minutiae improvements. There's probably 100 different designs you could do for this (it's kinda fun seeing them), if yours works conveniently with enough resolution for your purpose then it's clearly doing a good job!
Thank you very much for this video, especially the links to practical television which I never knew existed I thought they were long gone. I will be doing a lot of nostalgic reading. I recently built a pocket voltmeter using an esp8266 in a plastic box powered by a mobile phone battery so that I could read voltage on my phone over WiFi. I may be able to adapt this project to work with it.
@@michaeldranfield7140 I cant find the Television Magazine on that site now. Has it been removed? I still have some of the original magazines but have a lot of issues missing as my pocket money went missing too!
Certainly were good old days , I should have all the practical television magazines but there in no order, this has set me on a journey to do some other stuff and I have just found one of the television magazines I have been looking for in the airing cupboard ! , I'm going to have to sort them out into year file boxes, if only there was more hours in a day !
Thanks Michael for taking the trouble to find the printed article and directing us to getting a print of the article. Very useful video and I'm glad you've got your comments on - even if it means picking up some strange foreign comments (that need translating) along the way. PS Have now Subscribed to your channel.
Many thanks for that , the magazine took some finding because most of my magazines are in no order and I thought I made this from a copy of Everyday electronics magazine by mistake !, I keep seeing the comments in different languages buy dont reply as I cant read them .
Thank you for this video and the fantastic source of radio and TV information! I was hoping you'd give us a schematic and here you've given us the whole magazine and a ton more stuff on top of that! I'm recently retired and am just getting started in radio restorations. I'll repair anything that comes my way and may do some TVs if I find some worth restoring. The links you provided should be extremely helpful in both my learning and my restoration work!
The leads do not compensate for each other. If you like, you can make your probes with 4 wires of different lengths and gauges. It works by generating a constant current which is passed through the resistor being tested. The voltage produced is measured by the panel meter. Since the panel meter has a very high input impedance, it does not noticeably perturb the current. There is no compensation anywhere.
I have become accustomed to using the finger test to find out which is the component absorbing all of the power, but this is so much more refined an idea. First - this works even if there are poly fuses in the way that shut the power off before components get appreciably warm. Second, I find it difficult sometimes to work out exactly which of the components caused the painful burn (have been known to get the calipers out to try to measure the blister on my finger, to work out which component got hot).
A lot of circuits have current limiting and shut down when there us a short, only way to do the burnt finger test is power the rail from a bench power supply in a lot of cases.
Great idea! Some time ago I wanted to build a simple frequency counter and function generator but I found that there is no point in building one yourself when a Chinese device perfectly suitable for hobby use costs less than what I'd need to spend on parts. With a milliohm meter at least I stand a chance of breaking even! ;--)
Dear Michael, I would love to see your meter in action. That is, measuring some low value resistors, for example. Thank you for making and posting this video.
@@michaeldranfield7140 yes! Maximum applied current is 100 uA. Some components now days can be damaged with even 1 milliamp applied current. The 99 MA current of the homemade device could blow stuff out!
You are indeed correct but these days I am working without a service manual as the manifactures no longer produce schematic diagrams so there is nothing to loose, you would be horrified at my other method of short tracing when the short is above 1 ohm, I use a 10 amp bench power supply to power the rail and see what burns up!! By the way I watched your channel, very interesting, I see you are a valve person, or as they say in the states tube, I have just come across a very interesting solid state replacement for a very high voltage rectifier and plan to do a quick video very soon.
@@michaeldranfield7140 Been there done that! Another way is to run an amp through the short and use a thermal infrared camera to see what is heating up.
For short circuit fault finding it is better to have the output in the acoustic form (e.g. by the tone pitch,...) and with a relative reading mode (so you zero it on a value and it then indicate the lower resistances than that zero). In the 90's I remember such single purpose tester was published in our ham magazine ("A-radio" or the previous "Amaterske radio" named "Vyhledavac zkratu" aka "short circuit finder" or similar, it was published multiple times as various designs around the same principle). It used straight 2-pin connection, but the "zero memory" function took care of the probe wire resistance, so it did not need the 4 wire connection. It had just the beeper tone pitch as the main indication output and all the zeroing was by "remembering" the reference resistance as a voltage on a capacitor. It used a quad JFET opamp, one as the preaplifier, second as the "zero memory" sample and hold buffer (this was the part actually requiring the JFET inputs), 3'rd as a differential amplifier (amplifying the actual minus the stored value) and the 4th was the tone generator VCO. The sound output made the high current (30..40's mA test current from an 78L05) flowing for just a second, so the whole contraption could be made in the form of a probe supplied by a 9V battery. Components below 10Euro (my guess, prices according to the electronic component retail stores here). Today I would approach this using some microcontroller (an attiny45 or so, featuring a preamplifier for the ADC and working down to 1.8V, so it could be run from two AAA's), but keep the "user interface" essentially the same (a pushbutton for "zeroing", piezo for tone output, maybe just add a few LEDs as an additional bargraph style indication output), just implement the circuit HW way simpler and the "zero value" memory in a more stable digital form.
I'm pretty sure the same author published an audible millivolt meter a bit before this one and while it may be good for finding large variations of resistance I'm not sure if you would be able to detect a tone difference for 1 millivolt , I dont think it would be any good to me as my hearing is not as good as it use to be years ago ., but as lcd and led displays are so cheap now theres no excuse not to use one !
@@michaeldranfield7140 Well the point was you don't need to look at the display, but you could fully focus your eyes on where you are probing. So that way the work goes way faster. And for the sensitivity, if the amplifiers gain corresponds to the task, you can easily detect 10 uV or so (so way less than a mOhm at some 20mA or so test current) differences. The "zero reference memory" function and the differential indication were the key elements here, allowing the required gain so sensitivity. To find shorts, you don't need any accuracy, you just need to distinguish what is higher and what lower. It was a single purpose PCB short circuit finder tester tool, not a general use mOhm meter. It allows to find the shorts in a quick way, but that is all it can do, nothing else.
I designed a digital milliohmmeter and wrote an article and sold it to 2 different magazines in the 80’s and 90’s. One was Electronics and Wireless World Dec 1990 and Modern Electronics March 1989
When I was a kid and I use to go to the library with my mum on a Saturday morning they had all copies of electronics magazines you could read and one of them was Wireless world which I use to look at but did not understand due to the complex maths and it always seemed a magazine for industry rather than consumer and as such growing up, wireless world was a magazine I never bothered with .
@@michaeldranfield7140 Now you know my you tube alias has the same first letters of my real name! We had Radio Electronics and Popular Electronics when I was a kid. Circuit Cellar was just starting.
This is a Kelvin Probe. The two wires should be connected to each side of the spring clamping device as long as there is no resistance from each side of the clamp. . You have to take into account the there is mili Ohms of difference going through the clamp.
The TLE2425 is pretty nifty--I'll have to use it in an upcoming project. But meanwhile, what would you think of, instead of using a 7806 on the 2nd power supply, rather use a constant-current regulator, like a LM317 with a 12.5 ohm resistor? (That, I definitely could cobble from my junk box...)
Hi, thanks for a great video, i built an adapter to go on my multimeter with an LM317 as a constant current source, but it seems a bit flaky. I use it to test the ground connection on mobile radio car aerials. I think i'll build your one as its an all in one device. With mobile radio, a decent earth is fairly easy to achieve at VHF and UHF, but under 70mhz it becomes a lot more critical
I cant find the Television Magazine on that site now. Has it been removed? I still have some of the original magazines but have a lot of issues missing as my pocket money went missing too!
A small tip. When you have the entire magazine as a PDF in Acrobat Reader you can extract the three pages of interest as follows. Choose Print, select as your printer 'Microsoft Print to PDF'. In Pages to Print choose 'Pages' and '24 - 26'. Then click the print button and enter a file name.
That’s great I may have ago at developing a PCB for this. I have been thinking of buying one, the cheapest I have found is a Chinese one for about £130. They get good reviews but simple to make. Note some of the Chinese Kelvin clips are garbage but the version you have shown are ok.
something this simple you could draw the PCB by hand with a dalo pen and etch it in 20 minutes, a word of warning though when you warm up the ferric chloride to speed up the etching don't inhale the fumes , I did this by mistake a couple of months ago and its not nice .
Hi Michael I enjoyed watching this video however your description of how a kelvin clip works is wrong one wire of the pair forces a current into your device under test and the other lead of the two wire set measures the voltage and because the voltmeter is of high impedence this doesnt disturb reading too much not sure of the impedence of the panel meter but your fluke handheld should be of the order of 10 Megohm impedence on the volts range hope that helps
Yes indeed. It's a very strange mistake. He keeps saying the wires are in parallel, and that it works because of the geometry, yet he built the thing, so he knows perfectly well that they are connected to different points inside the box, as we can see on the video. in any case the correct explanation is provided in the article. He's also wrong about the current drain. Current only flows when the probes are connected to a resistance, or of course if shorted together. And that's another thing the buzzer is for. Again this is mentioned in the article.
Firstly most of my videos contain small mistakes, and if your saying current is only drawn when the probes are shorted how come the led display is lit as soon as the unit is switched on.
@@michaeldranfield7140 I agree with you but i didnt say that current only flows when connected to a resistance. I think what @EJP was trying to convey was current is only drawn through the probes when they are shorted. Obviously current is drawn for the electronics in the milliohmmeter.
@Michael Danfield This is not a 'small error', it is a major mistake. As to the current, you waved at the RHS of the circuit and stated it drew a lot of current all the time, hence no battery. It draws zero when unconnected.
Great video Michael. Found your site by accident and loving the style and quality of advice - even if I don't fix TVs! Your link to the World Radio site is so useful and I have spent a few hours now browsing old editions of Wireless World which I purchased as a schoolboy and later a student in the 1970s. Where abouts in the UK are you based in case my LG OLED fails?
im in Derbyshire , the world radio site is very interesting , I have paper copies of most of the magazines but some magazines like wireless world I never took as a kid so world radio is a very useful reference .
I would think that any precision reference voltage generator chip giving the correct output would be fine, in fact as this is quite an old project I would imagine there are many better specified devices than the original .
When I was on the bench in early 70's for MOD I used a Marconi bridge to detect shorts from 5V to 0V which crowbarred the PSU. Usually had 100 DTL chips on a board and the short was always under a chip.
Invaluable no there are no schematics, would have been a nightmare in the days of TTL as you say with a hundred chip doing the same as just one would do today.
If i want to run it on an external power supply (6volt). How do i separate the power if i want to build your version with a display? Do i need two power supplies?
@@michaeldranfield7140 mV-meters readings must be multiplied by 10? In one of your old video where you showed how to trace dead short in-circuit, your mV reading was 0.375mV so multiplied by 10 will be 3.75mV wich means 3.75 mOhm. Am I understanding it right?
@@michaeldranfield7140 after I watched your original video I went looking on TH-cam for similar. I found this, its not as elegant as yours. I hope youtube don't remove the link th-cam.com/video/P_2GGNr4q1s/w-d-xo.html
While I do not plan on building this, I think a worthwhile upgrade would be to use 18650 batteries. They are rechargeable, commonly available,have good capacity and you do not have to mess with having to plug it in to use it.
Not really as its so simple I didn't draw a schematic, its just a 6 Volt regulator IC 7806 and whatever power the digital voltmeter needs, 5 volt I think, have a search on the net for 3 terminal regulator 7805 , I think it was for the panel meter , .
hello Michael, a happy 2023! If possible, I would like you to send me some links to electronic circuit assembly sites and test equipment. Here in Brazil, we have little information on these matters!!! Hug happiness.
I don't use electronic sites , most of my projects come from magazines I have collected for the last 40 plus years, however there is a site on the internet called " world radio history" and you can download most of the electronics magazines from there , everyday electronics , practical wireless , there's load of them , going back years .
Sir so nice and kind, sir what are the values of ur addition like bridge rectifiers, capacitors and linear regulators etc and how they were connected, 2ndly are the 2 mobile phone chargers of 5v not used? 1 for miliohm circuit and 2nd for digital meter, please guide as m a fresher. Also any substitute for TLE2425 ic..,. , Be Blessed and live happily ever
Hi Michael. Thank you for creating this informative video, this is going to be my holiday project. If you have time, I was wondering if you knew what the difference was between TLE2425CLP and TLE2425ILP. I'm not sure if they're interchangeable for the purposes of this project. The data sheet says the only difference is the device marking (2425C and 2425I respectively). I'm guessing the C or I before the LP is the version number? (LP refers to PLASTIC TO-226AA). Thanks in advance.
C is rated 0-70 degrees (celcius), I is rated -40 to 85 degrees, M is rated -55 to 125 degrees. At least for the TI part. That means if you buy the I version, they guarantee it will operate within its min/max specs even if you left it in an oven at 100 degrees. For this project you could use any. If you build this, the easiest way to get decent precision is by putting the kelvin leads onto a multimeter in ammeter mode, and swapping out R3/R4 until it shows exactly 100mA is being drawn.
This is mostly a DC device, the NE5534 is designed especially for it's AC properties (i.e... audio.). You can get any number of better DC performance opamps than an NE5534 these days and for around the same cost.
It would have been nice if you credited Alan Wilcox as he designed the unit. It was his intention to make it as simple as possible and not require a panel meter as at the time of publication cheap digital volt meters cost as little as £2.50. The circuit only pulls 100ma when the probes are attached to a short, no need to worry about batteries, you can leave it on forever and the batteries will be fine. (Alan Wilcox was a personal friend of mine,)
His name appears in the Television artical for all to see, while the original design draws no current when the probes are not shorted mine has a big red LED display which is drawing current all the time so could not be left on all the time without draining batteries, and there is a very good reason I did not refer to the author I have it in the back of my mind he is no longer with us but as I cant be absolutely sure I decided it was best to say nothing , but I am sure anyone who downloads a copy of the magazine will see the authors name .
@@michaeldranfield7140 Alan would be very happy to see his work is being used. He has many publications mainly in old electronics magazines. And more recently in Maplins magazine(can't remember what it was called) for a very low distortion oscillator which was stabilised using a small bulb, he used it in his MK1 ESR meter and found it wasn't necessary to have such a pure sign wave. His MK2 ESR meter was quite popular.
If anyone downloads the PDF of the Magazine & you read, open it up in a reader, its pages 24-25-26 / 68 RS have the components. Chip - OP-Amp in stock 6/6/2022
RS components are a trusted source, as are Farnell components and no doubt there are other trusted sources, I only mentioned RS as I have an account with them.
I have used mouser and digikey in the past but they both had high order charges, as an account holder with RS I get free delivery over £5, I know all these other places cost more but at the end of the day your paying more for peace of mind the parts are genuine, I have had too much fake crap over the years.
As you said its worth paying the extra higher chargers, knowing your going to get a good working genuine part/component. I always pay for tracking for the extra safety. Oh I forgot to say before, I used to use' Maplins until they closed down as they we're local and easy some years back, Never had a bad component from them.
I've been looking and see Rapid electronics in the UK have the TL071 OP Amp but not the LP package of the TLE2425 but at least its another good source, I'm sure if i ask - request, it could be ordered I guess, they've also been a good reliable source in the past.
Can I use two lithium-ion batteries and just run it on 8.4V instead of 6V? Maybe put a 10ohm resistor in series with the batteries? In the magazine they refer to using audio coax cable soldering the shield to the core at the tip. I could just get test lead ends and a stereo RCA patch cord cutting off one end, soldering them onto the test leads. Then install a female RCA connector into the case and be sure to run the 100ma high current through the outer shields. At that point one could run the audio cable core out with banana plugs to use with an external DVM or install in the case one of those cheap E-bay 200mv panel voltage meters into the case.
I don't really miss the game now, I got out in the late 90s, did university, ended up in data and telecoms, but approaching 60, I'm enjoying playing about with electronics again.
@@simontopley4771 The decline of TV repairs started when we went digital , you wouldn't miss it now , its all board replacement ,hardly any component level fault finding as there are no service manuals anymore .
Your Kelvin clips aren't exactly right. The two leads should each occupy a separate side of the clips, not come into the same side as you have shown. I love the proto build, very clean!
Help me understand something... if a cheapo meter costs $40, why in the world would a meter with 4 terminals to cancel out the resistance cost hundreds? I was blown away by the simplicity of the circuit and I just don't understand the price jump....
You CAN build/sell a far higher precision and accuracy meter for hundreds... whether a particular one is actually built for superior specifications or just has some historical price markup that chumps will pay, well depends.
Actually, the current leads and the voltage leads can’t touch each other at the device being measured. They should be close together, but not touching.
Sure they can. Electrically it's basically equivalent. The closer the touch point to the real resistance path desired to measure the better, although you start to get diminishing returns. Probably slightly better kelvin clips could be made by having each wire go to an opposing side of the clip so they only touch when it gets full grip on something. As pointed out in the video, if you're making a micro-ohm meter the distinction probably matters, but for the as-designed milli-ohm meter, not really.
Thanks so much for posting this. Could you just confirm that the 'Panel Meter' you mention should be a Voltage meter with a Measurement Range: 0 ~ 200mV DC? You said 'resolution' rather than measurement range. This is the only bit that confused me.
If just finding relative resistance, wouldn't a constant current source (cc of bench psu) and dmm be sufficient? For absolute readings, use a precision resistance calibration sample.
If you apply some current, less than the normal consumption, to the power supply side (3v3, 5v etc) you can use the millivolt range of a good multimeter to do exactly the same.. The voltage at the short circuit is the lowest. Before the short there is a drop in voltage. Further away behind the short the voltage stays the same.
I just found it convenient to have an all in one tester rather than using a separate meter, but as you and others have said there is more ways to do the same job.
Using Kelvin's strategy, the current is supplied and measured using I+ and I- leads and the voltage is sensed using separate V+ and V- leads. The voltmeter has high internal resistance so very little current flows in the sense leads and the voltage across the sense leads, V=(0)r, approaches zero... the voltmeter measures the voltage actually across the DUT. The current leads do develop an additional voltage, V=Ir, but this is NOT the voltage used to compute the device's resistance, R=(V+ -- V-)/I. As long as the sense leads are connected directly to the test resistance, R is rather exactly equal to that resistance. If you must do even better, you can add a guard shell around the current leads to eliminate leakage current and you can compensate for sense lead resistance by applying the voltage divider to the lead resistance and the voltmeter's resistance.
Many thanks for the excellent explanation.
I was very confused from the explanation in the video, because I was certain that this was simply a 4-wire measuring setup, which it is.
It's not about canceling the resistance offset, which would be very easy with an offset pot.
It's about having one pair of wire for the current itself, and a second wire pair to sense the actual voltage drop, however drawing as little current as possible to cause no voltage drop over the wires itself.
I think the video is actually quite misleading.
@@graealex For those of us who would have a use for this device the video makes perfect sense.
The device passes current across the test points. A separate DVM measures the voltage drop across those two points.
For every 1 miliohm resistance across the two test points causes a 1 milivolt voltage potential [difference] across those two test points.
[1Mv = .001volt] [1Mohm = .001ohm]
@@DrHarryT The problem is that Michael gave a completely different (and unfortunately wrong) explanation to how it works. Maybe watch the video again.
Your explanation on how it is supposed to work is absolutely fine. One component is generating a constant current (a constant current source, easily implemented with a const current driver), and a second component (DMM voltage measurement) is measuring the voltage drop.
@@graealex Yup, maybe I should watch it again, the first time I probably filled in the blanks or referred to my own understanding of how it works.
Thank you mr Dranfield for all your hard work getting these videos out there for us to enjoy and learn.Your wealth of knowledge and experience is invaluable.
Glad you liked it , a very useful tool , its not something you use every day but when you do its a lifesaver .
I want to thank you again Michael for alerting me to this circuit (and thanks to Alan Wilcox for the original design!). I have now constructed my own unit. I already had a suitable enclosure and the majority of components, so the whole thing cost me about £28 (kelvin leads & panel meter accounting for £21). I am truly astonished by the accuracy! I've powered it with 3 x 18650 batteries (including separate supply for the meter) and included recharging sockets.
nice one , and about 20 times cheaper than buying one , as you say incredibly accurate, I had a complaint from a viewer that I made no reference to the original author of the project and I did this because I have a feeling Alan is no longer with us but I cant be 100 percent sure so I thought it was better to say nothing .
Thank You! I didn't know how usefull it is until I watched your videos, I've been repairing electronics most of my life, fifty at less( I'm 62)...
Same here and I'm not that far behind you at nearly 58. if you have watched the video where I can pick out a single diode from 3 in paralleled you will have realized just how useful this is .
@@michaeldranfield7140 That video and one video about finding a short on tv screen with those CML 10 uF capacitors, I used to take them one by one until the short disapears, this instrument saves a lot of time.
With it and my old scopemeter PM97 by now the two most usefull instruments!
Thank you for taking the time to provide the details and background info on this. I am definitely going to build one and will follow much of the layout you did, perhaps with some minor changes but mains powered and an LED panel meter will be part of my unit.
It's a good tool and so cheap to make.
World Radio History is a fantastic resource, I’ve been using it for some time. Considering it’s an American site, he has managed to scan an amazing number of British magazines and books.
Thanks for a very useful video and especially for the advice about avoiding fake components!
Very useful as you say, I am very lucky to have the paper copies though.
Oh man, how complicated is that! It's just a constant current source and the good old LM317T precision regulator with just a resistor and just about any power supply found in the junk box would have done the same job. But I have to say: he did it very neatly and beautifully! A real gem of DIY!
I get a lot of pleasure out of building stuff myself , its what I have always done .
Thanks Michael for the great video and very helpful instructions. I made one, works great. As yours, mine uses a small spare mains transformer with 2 secondary windings. This is very important as you mention because most digital displays use a common ground with the measurement circuit and supply. My meter is 12V supply but I see others using 5V or similar. A 7806 regulator gives a nice stable supply for the measuring part as per the schematic. The kelvin probes are readily available so all in all a great addition to the test bench, thanks again.
Glad you liked it , its not something I use on a daily basis but when you need it its really useful and saves a lot of time disconnecting things.
Thank you for sharing this, a great added bonus is the way you made it to run off mains, I look forward to having a go at it
I made it run from the mains so i dont have to worry about turning it off !
Ha! What a gift! Thank you! I have already downloaded the July 2005 PDF and I plan to source my components soon. Top stuff! You are a star!
No problem , many thanks for watching .
I watched your video with great interest, where you found a SMD Capacitor shorted-out on that TV Time Control Circuit. You used your milliohm meter in order to pinpoint the short! I had never realised that you could do this. I have always removed many transistors, capacitors to check if the current flow had gone down in the circuit. Also, I have used cooling & heating various items on the PCB - to effect change (hopefully). Short circuits aren't real easy to locate, well, not for me anyway. Thanks for your contribution in teaching those that are well-under your level of knowledge! Greetings from Sydney.
It's only good when the short is less than 1 ohm, above this what I do is to apply a voltage from a bench power supply and see what gets hot.
Yeah, I was going to say the same thing - apply power from a bench supply, but below the usual rail voltage of the shorted rail so things don't actually turn on. Use 1V, and give it lots of current - the offending component will soon identify itself by melting, lighting on fire, or having your finger print permanently burned into it as you hunt around the board for what gets hot
Which Video was it, I may of missed that one.
@@andywebber8749 It was a video to highlight the problems of repairing flat screen TV sets .
@@andywebber8749 Hi Andy, you need to look for: "Flat screen TV, a very common fault to look out for". I currently have a 42" LG LCD TV with the right side of the screen with just vertical coloured lines. I have already changed the Main Board, and replaced the T-Con. Nothing changed. I don't have a milliohmeter, but (taking Michael Dransfield's lead), I will definitely remove the top section of this TV, (after the T-Con Board) to reveal the ribbon that carries these SMD Capacitors, and simply change-out the whole lot. I really wish that Michael lived next door to me!! greetings from Australia.
Thanks for sharing with us such as good information in general not only with this one. I hate watching a lot of industrial components been throwing away becouse a one small components which cost not even £0.2 stopping working equipment worth a thousands of pounds.
You can also find a self-designed from-scratch milliohmmeter from another great british electronics youtuber, Scullcom Hobby Electronics (video #31 and #43). I appreciate seeing your own design and it's source. That that website is preserving all those magazines digitally (for free!) is a great resource. I bet there are some really neat simple hobby designs scattered throughout the 1000s of pages of magazines you could peruse there.
I'm pretty sure it doesn't matter if you connect the voltmeter's ground to the current sink's ground, as long as the voltmeter is doing a proper differential voltage measurement on its +/- wires. Completely isolating it probably doesn't hurt with stability though.
Funny seeing a lot of comments exclaiming minutiae improvements. There's probably 100 different designs you could do for this (it's kinda fun seeing them), if yours works conveniently with enough resolution for your purpose then it's clearly doing a good job!
Many thanks for that .
Thank you so much for this video. I just subscribed because of this. You really help people solve problems, and also, revive some forgotten knowledge.
Thank you very much for this video, especially the links to practical television which I never knew existed I thought they were long gone. I will be doing a lot of nostalgic reading. I recently built a pocket voltmeter using an esp8266 in a plastic box powered by a mobile phone battery so that I could read voltage on my phone over WiFi. I may be able to adapt this project to work with it.
Television magazine went bust over 10 years ago but someone has put them on the Web, I'm lucky to have all the paper versions.
@@michaeldranfield7140 I cant find the Television Magazine on that site now. Has it been removed?
I still have some of the original magazines but have a lot of issues missing as my pocket money went missing too!
Yes still available look under just "Television" on the left hand side
Thank you very much for this. Much appreciated.
No problem , many thanks for watching .
Thank you for tracking down the info Michael - much appreciated.
Took a while to find because I thought it was in everyday practical electronics so I was searching in the wrong place.
Thank you for sharing that Michael. I am now turning on my computer and printer. 👍
Dead easy to make as long as you don't use fake components!
Super video and good info.Keep up the good work and nice to see an old practical television mag on show, ahh Good days....Cheers...
Certainly were good old days , I should have all the practical television magazines but there in no order, this has set me on a journey to do some other stuff and I have just found one of the television magazines I have been looking for in the airing cupboard ! , I'm going to have to sort them out into year file boxes, if only there was more hours in a day !
Thanks Michael for taking the trouble to find the printed article and directing us to getting a print of the article. Very useful video and I'm glad you've got your comments on - even if it means picking up some strange foreign comments (that need translating) along the way. PS Have now Subscribed to your channel.
Many thanks for that , the magazine took some finding because most of my magazines are in no order and I thought I made this from a copy of Everyday electronics magazine by mistake !, I keep seeing the comments in different languages buy dont reply as I cant read them .
@@michaeldranfield7140 copy and paste the comments into google translate. you can reply the same way.
Thanks for sharing - nice to see your embellishments too!
No problem, thanks for watching.
Thanks for sharing. Lots of awesome articles just love the old magazines.
It seems like most of the old magazines are on the net, luckily I have all the paper copies.
I’ve got one of the RS ones (it’s branded Rhopoint though). I rescued it from a skip at work, I had no idea they were that expensive!
Anything branded RS is expensive.
Thank you for this video and the fantastic source of radio and TV information! I was hoping you'd give us a schematic and here you've given us the whole magazine and a ton more stuff on top of that! I'm recently retired and am just getting started in radio restorations. I'll repair anything that comes my way and may do some TVs if I find some worth restoring. The links you provided should be extremely helpful in both my learning and my restoration work!
No problem at all, glad I have been some use to you, if I was retired I would a lot more time to do stuff like this.!
The leads do not compensate for each other. If you like, you can make your probes with 4 wires of different lengths and gauges.
It works by generating a constant current which is passed through the resistor being tested. The voltage produced is measured by the panel meter. Since the panel meter has a very high input impedance, it does not noticeably perturb the current. There is no compensation anywhere.
Great stuff! Your series is so practical. Thanks.
Many thanks for that.
I have become accustomed to using the finger test to find out which is the component absorbing all of the power, but this is so much more refined an idea. First - this works even if there are poly fuses in the way that shut the power off before components get appreciably warm. Second, I find it difficult sometimes to work out exactly which of the components caused the painful burn (have been known to get the calipers out to try to measure the blister on my finger, to work out which component got hot).
A lot of circuits have current limiting and shut down when there us a short, only way to do the burnt finger test is power the rail from a bench power supply in a lot of cases.
Very nice indeed. I will build this, in the form you describe as it is nicely thought out.
Also very simple considering it will cost you well over £400 to buy a commercial made one, many thanks for watching.
Great idea! Some time ago I wanted to build a simple frequency counter and function generator but I found that there is no point in building one yourself when a Chinese device perfectly suitable for hobby use costs less than what I'd need to spend on parts. With a milliohm meter at least I stand a chance of breaking even! ;--)
Of course but a lot of the stuff i have was built before the Chinese flooded the market with cheap test equipment .
Pleasant and entertaining while very instructive. Thanks, Sir!
No problem , many thanks for watching .
Dear Michael, I would love to see your meter in action. That is, measuring some low value resistors, for example. Thank you for making and posting this video.
I made a couple of videos in the last week or so where I used it to trace a shorted out, and one where I used it to find a shorted out capacitor.
@@michaeldranfield7140 Thank you Michael. Excellent video, and I love that low ohms meter. (I'll look for your videos. Thank you). God[Bible] Bless.
Refreshingly simple - it makes me wonder how much more is inside the RS unit!
Is int it, I would think the RS one contains much the same stuff !
@@michaeldranfield7140 yes! Maximum applied current is 100 uA. Some components now days can be damaged with even 1 milliamp applied current. The 99 MA current of the homemade device could blow stuff out!
You are indeed correct but these days I am working without a service manual as the manifactures no longer produce schematic diagrams so there is nothing to loose, you would be horrified at my other method of short tracing when the short is above 1 ohm, I use a 10 amp bench power supply to power the rail and see what burns up!!
By the way I watched your channel, very interesting, I see you are a valve person, or as they say in the states tube, I have just come across a very interesting solid state replacement for a very high voltage rectifier and plan to do a quick video very soon.
@@michaeldranfield7140 Been there done that! Another way is to run an amp through the short and use a thermal infrared camera to see what is heating up.
Would be great to see other home made projects you built!
Its coming !
At the moment my problem is not enough hours in the day .
Very big Thank You Michael. Always simple when you know. Thank You So Much cheers. 73
No problem , many thanks for looking .
For short circuit fault finding it is better to have the output in the acoustic form (e.g. by the tone pitch,...) and with a relative reading mode (so you zero it on a value and it then indicate the lower resistances than that zero). In the 90's I remember such single purpose tester was published in our ham magazine ("A-radio" or the previous "Amaterske radio" named "Vyhledavac zkratu" aka "short circuit finder" or similar, it was published multiple times as various designs around the same principle). It used straight 2-pin connection, but the "zero memory" function took care of the probe wire resistance, so it did not need the 4 wire connection. It had just the beeper tone pitch as the main indication output and all the zeroing was by "remembering" the reference resistance as a voltage on a capacitor. It used a quad JFET opamp, one as the preaplifier, second as the "zero memory" sample and hold buffer (this was the part actually requiring the JFET inputs), 3'rd as a differential amplifier (amplifying the actual minus the stored value) and the 4th was the tone generator VCO. The sound output made the high current (30..40's mA test current from an 78L05) flowing for just a second, so the whole contraption could be made in the form of a probe supplied by a 9V battery. Components below 10Euro (my guess, prices according to the electronic component retail stores here).
Today I would approach this using some microcontroller (an attiny45 or so, featuring a preamplifier for the ADC and working down to 1.8V, so it could be run from two AAA's), but keep the "user interface" essentially the same (a pushbutton for "zeroing", piezo for tone output, maybe just add a few LEDs as an additional bargraph style indication output), just implement the circuit HW way simpler and the "zero value" memory in a more stable digital form.
I'm pretty sure the same author published an audible millivolt meter a bit before this one and while it may be good for finding large variations of resistance I'm not sure if you would be able to detect a tone difference for 1 millivolt , I dont think it would be any good to me as my hearing is not as good as it use to be years ago ., but as lcd and led displays are so cheap now theres no excuse not to use one !
@@michaeldranfield7140 Well the point was you don't need to look at the display, but you could fully focus your eyes on where you are probing. So that way the work goes way faster. And for the sensitivity, if the amplifiers gain corresponds to the task, you can easily detect 10 uV or so (so way less than a mOhm at some 20mA or so test current) differences. The "zero reference memory" function and the differential indication were the key elements here, allowing the required gain so sensitivity.
To find shorts, you don't need any accuracy, you just need to distinguish what is higher and what lower.
It was a single purpose PCB short circuit finder tester tool, not a general use mOhm meter. It allows to find the shorts in a quick way, but that is all it can do, nothing else.
I designed a digital milliohmmeter and wrote an article and sold it to 2 different magazines in the 80’s and 90’s. One was Electronics and Wireless World Dec 1990 and Modern Electronics March 1989
When I was a kid and I use to go to the library with my mum on a Saturday morning they had all copies of electronics magazines you could read and one of them was Wireless world which I use to look at but did not understand due to the complex maths and it always seemed a magazine for industry rather than consumer and as such growing up, wireless world was a magazine I never bothered with .
Page 1078 , many thanks for that , I have just looked it up on the internet .
@@michaeldranfield7140 Now you know my you tube alias has the same first letters of my real name! We had Radio Electronics and Popular Electronics when I was a kid. Circuit Cellar was just starting.
Of all the lucky videos to stumble across!!!!! Excellent tip about fake components, becoming more and more common from China, sadly.
This is a Kelvin Probe. The two wires should be connected to each side of the spring clamping device as long as there is no resistance from each side of the clamp. . You have to take into account the there is mili Ohms of difference going through the clamp.
The TLE2425 is pretty nifty--I'll have to use it in an upcoming project. But meanwhile, what would you think of, instead of using a 7806 on the 2nd power supply, rather use a constant-current regulator, like a LM317 with a 12.5 ohm resistor? (That, I definitely could cobble from my junk box...)
No reason you can't use a LM317, I only used the 78 series for simplicity, just decouple the input and output and you have an instant power supply.
@@michaeldranfield7140 7805 and 7905 for -5v?
Hi, thanks for a great video, i built an adapter to go on my multimeter with an LM317 as a constant current source, but it seems a bit flaky. I use it to test the ground connection on mobile radio car aerials. I think i'll build your one as its an all in one device. With mobile radio, a decent earth is fairly easy to achieve at VHF and UHF, but under 70mhz it becomes a lot more critical
Excellent, I think thus would also find application in other car related things such as checking the battery negative to chassis integrity.
@@michaeldranfield7140 I drive an electric car LOL!
Many thanks 🙏🏻 you truly are a gentleman 👍🏻🇬🇧
No problem at all, many thanks for watching.
As an old TV engineer myself I was wondering if Practical Television is still going these days? Great video by the way!
No, it went bust over 10 years ago after they replaced the editor with someone who had no electronics background.
@@michaeldranfield7140 Well that was an extremely Stupid move
Hello Michael! Where can I get a schematic to assemble one of these milliohmmeters? Or do you sell this model in the video?
Go to a site on the internet called
"World radio history " and you can download the whole magazine it was published in .
I cant find the Television Magazine on that site now. Has it been removed?
I still have some of the original magazines but have a lot of issues missing as my pocket money went missing too!
worldradiohistory.com/UK/Practical/Television/00s/Television-2005-07.pdf here you go, direct link as I also had trouble finding it.
Excellent, Michael. Many thanks!
No problem, glad you liked it.
A small tip. When you have the entire magazine as a PDF in Acrobat Reader you can extract the three pages of interest as follows. Choose Print, select as your printer 'Microsoft Print to PDF'. In Pages to Print choose 'Pages' and '24 - 26'. Then click the print button and enter a file name.
Might be useful to others , I have all these magazines in paper form .
What voltage are the 2 voltage regulators? And how much voltage does this circuit inject in the circuit you are testing?
That’s great I may have ago at developing a PCB for this. I have been thinking of buying one, the cheapest I have found is a Chinese one for about £130. They get good reviews but simple to make. Note some of the Chinese Kelvin clips are garbage but the version you have shown are ok.
something this simple you could draw the PCB by hand with a dalo pen and etch it in 20 minutes, a word of warning though when you warm up the ferric chloride to speed up the etching don't inhale the fumes , I did this by mistake a couple of months ago and its not nice .
Hi Michael I enjoyed watching this video however your description of how a kelvin clip works is wrong one wire of the pair forces a current into your device under test and the other lead of the two wire set measures the voltage and because the voltmeter is of high impedence this doesnt disturb reading too much not sure of the impedence of the panel meter but your fluke handheld should be of the order of 10 Megohm impedence on the volts range hope that helps
Yes indeed. It's a very strange mistake. He keeps saying the wires are in parallel, and that it works because of the geometry, yet he built the thing, so he knows perfectly well that they are connected to different points inside the box, as we can see on the video. in any case the correct explanation is provided in the article.
He's also wrong about the current drain. Current only flows when the probes are connected to a resistance, or of course if shorted together. And that's another thing the buzzer is for. Again this is mentioned in the article.
Firstly most of my videos contain small mistakes, and if your saying current is only drawn when the probes are shorted how come the led display is lit as soon as the unit is switched on.
@@michaeldranfield7140 I agree with you but i didnt say that current only flows when connected to a resistance. I think what @EJP was trying to convey was current is only drawn through the probes when they are shorted. Obviously current is drawn for the electronics in the milliohmmeter.
@Michael Danfield This is not a 'small error', it is a major mistake. As to the current, you waved at the RHS of the circuit and stated it drew a lot of current all the time, hence no battery. It draws zero when unconnected.
Great video Michael. Found your site by accident and loving the style and quality of advice - even if I don't fix TVs! Your link to the World Radio site is so useful and I have spent a few hours now browsing old editions of Wireless World which I purchased as a schoolboy and later a student in the 1970s. Where abouts in the UK are you based in case my LG OLED fails?
im in Derbyshire , the world radio site is very interesting , I have paper copies of most of the magazines but some magazines like wireless world I never took as a kid so world radio is a very useful reference .
Great inspirational video thanks Michael
Many thanks .
Any substitute for TLE2425CLP ic as unable to find in the local market.,., thx
I would think that any precision reference voltage generator chip giving the correct output would be fine, in fact as this is quite an old project I would imagine there are many better specified devices than the original .
Thanks Michael from Italy
no problem , many thanks for watching .
Thank You Michael! Great video!
many thanks for watching .
When I was on the bench in early 70's for MOD I used a Marconi bridge to detect shorts from 5V to 0V which crowbarred the PSU. Usually had 100 DTL chips on a board and the short was always under a chip.
Invaluable no there are no schematics, would have been a nightmare in the days of TTL as you say with a hundred chip doing the same as just one would do today.
Was that diode Transistor logic. I have memories off this but a bit before my time.
Thanks for the video,
You can also get cheap Chinese PCB ones for £40.
not as good as making your own though .
It was a joy to watch this video ! And yes, us old farts like to build our own equipment 👍🏻🤝🏻🇳🇱
many thanks for watching .
Sometimes things that may look trivial like using a double cable for probes is not considered when designing electronic circuits.
If i want to run it on an external power supply (6volt). How do i separate the power if i want to build your version with a display? Do i need two power supplies?
Very nice project! Thanks for sharing.
No problem , glad you liked it .
@@michaeldranfield7140 mV-meters readings must be multiplied by 10? In one of your old video where you showed how to trace dead short in-circuit, your mV reading was 0.375mV so multiplied by 10 will be 3.75mV wich means 3.75 mOhm. Am I understanding it right?
@@dextertech6570 in this design resolution is 1 Mv, its a direct reading and needs no multiplication
@@michaeldranfield7140 Thank you, sir
Well done finding it. Thanks for sharing.
No problem at all, many thanks for watching.
Thank you sir ive been looking forward to this.
No problem, many thanks for watching.
@@michaeldranfield7140 after I watched your original video I went looking on TH-cam for similar. I found this, its not as elegant as yours. I hope youtube don't remove the link th-cam.com/video/P_2GGNr4q1s/w-d-xo.html
While I do not plan on building this, I think a worthwhile upgrade would be to use 18650 batteries. They are rechargeable, commonly available,have good capacity and you do not have to mess with having to plug it in to use it.
of course , if you wanted portability .
If the device is always in one's workshop, on the other hand, a power point is likely very easy to come by
Does TL431 replace tl2425?
Will a DMS-20PC-0-RS fit as a voltmeter?
Any volt meter with a FSD of 200 M/V will do , then just make a power supply to power the voltmeter .
I do not have TLE2425. Could I use TL431?
I don't see why not but you would have calculate the resistance values to get the correct voltage reference, much easier to just buy the correct chip.
@@michaeldranfield7140 I asked because in my town don't have the chip indicated on your video. TL431 came to my mind due to the reference voltage.
Hi can you show us a drawing of the power supply and list the components used please
Not really as its so simple I didn't draw a schematic, its just a 6 Volt regulator IC 7806 and whatever power the digital voltmeter needs, 5 volt I think, have a search on the net for 3 terminal regulator 7805 , I think it was for the panel meter , .
hello Michael, a happy 2023! If possible, I would like you to send me some links to electronic circuit assembly sites and test equipment. Here in Brazil, we have little information on these matters!!!
Hug happiness.
I don't use electronic sites , most of my projects come from magazines I have collected for the last 40 plus years, however there is a site on the internet called " world radio history" and you can download most of the electronics magazines from there , everyday electronics , practical wireless , there's load of them , going back years .
Sir so nice and kind, sir what are the values of ur addition like bridge rectifiers, capacitors and linear regulators etc and how they were connected,
2ndly are the 2 mobile phone chargers of 5v not used? 1 for miliohm circuit and 2nd for digital meter, please guide as m a fresher. Also any substitute for TLE2425 ic..,. , Be Blessed and live happily ever
Great project 🙂
I have send you a email regarding a public link to the magazine you mentioned. Grtz
ok , many thanks .
Not received an e mail yet, do you have my correct one. md@digifixltd.co.uk
@@michaeldranfield7140 hi, i had it send to another mail adress, you should now have received my email at md@.......
Thank you. Grtz
Wow! That magazine started in 1950.
a lot of magazines have history behind them , I think practical wireless started in the 1920 s for example ,
Hi Michael. Thank you for creating this informative video, this is going to be my holiday project.
If you have time, I was wondering if you knew what the difference was between TLE2425CLP and TLE2425ILP. I'm not sure if they're interchangeable for the purposes of this project.
The data sheet says the only difference is the device marking (2425C and 2425I respectively).
I'm guessing the C or I before the LP is the version number?
(LP refers to PLASTIC
TO-226AA). Thanks in advance.
C is rated 0-70 degrees (celcius), I is rated -40 to 85 degrees, M is rated -55 to 125 degrees. At least for the TI part. That means if you buy the I version, they guarantee it will operate within its min/max specs even if you left it in an oven at 100 degrees.
For this project you could use any.
If you build this, the easiest way to get decent precision is by putting the kelvin leads onto a multimeter in ammeter mode, and swapping out R3/R4 until it shows exactly 100mA is being drawn.
I dont know off the top of my head but it could be one is lead free and the other is not .
Where can i find tle2425 or can you tell me replacement for it?
have a look ar RS components , however as its only a precision voltage reference chip any other chip giving the same output voltage should work fine .
Thank you for quick response sir 🙂
new fan here! loved the video❤.
I prefer to use NE5534 instead of TL071, less noise in the signal and therefore probably more accurate.
This was a very old project and as you say there will be much better chips to use these days but the TL071 was good enough in its day .
This is mostly a DC device, the NE5534 is designed especially for it's AC properties (i.e... audio.). You can get any number of better DC performance opamps than an NE5534 these days and for around the same cost.
Are those the original fluks test leads they look like cheap ones?
It would have been nice if you credited Alan Wilcox as he designed the unit. It was his intention to make it as simple as possible and not require a panel meter as at the time of publication cheap digital volt meters cost as little as £2.50. The circuit only pulls 100ma when the probes are attached to a short, no need to worry about batteries, you can leave it on forever and the batteries will be fine. (Alan Wilcox was a personal friend of mine,)
His name appears in the Television artical for all to see, while the original design draws no current when the probes are not shorted mine has a big red LED display which is drawing current all the time so could not be left on all the time without draining batteries, and there is a very good reason I did not refer to the author I have it in the back of my mind he is no longer with us but as I cant be absolutely sure I decided it was best to say nothing , but I am sure anyone who downloads a copy of the magazine will see the authors name .
@@michaeldranfield7140 Alan would be very happy to see his work is being used. He has many publications mainly in old electronics magazines.
And more recently in Maplins magazine(can't remember what it was called) for a very low distortion oscillator which was stabilised using a small bulb, he used it in his MK1 ESR meter and found it wasn't necessary to have such a pure sign wave.
His MK2 ESR meter was quite popular.
@@walescmo If my memory serves me correctly he also did an in circuit transistor tester in about 1976 .
@@michaeldranfield7140 yes we used it allot
If anyone downloads the PDF of the Magazine & you read, open it up in a reader, its pages 24-25-26 / 68 RS have the components. Chip - OP-Amp in stock 6/6/2022
RS components are a trusted source, as are Farnell components and no doubt there are other trusted sources, I only mentioned RS as I have an account with them.
That makes 2 of us then Michael! :) I also use' Farnell, Mouser & Digikey.
I have used mouser and digikey in the past but they both had high order charges, as an account holder with RS I get free delivery over £5, I know all these other places cost more but at the end of the day your paying more for peace of mind the parts are genuine, I have had too much fake crap over the years.
As you said its worth paying the extra higher chargers, knowing your going to get a good working genuine part/component. I always pay for tracking for the extra safety. Oh I forgot to say before, I used to use' Maplins until they closed down as they we're local and easy some years back, Never had a bad component from them.
I've been looking and see Rapid electronics in the UK have the TL071 OP Amp but not the LP package of the TLE2425 but at least its another good source, I'm sure if i ask - request, it could be ordered I guess, they've also been a good reliable source in the past.
Can I use two lithium-ion batteries and just run it on 8.4V instead of 6V? Maybe put a 10ohm resistor in series with the batteries?
In the magazine they refer to using audio coax cable soldering the shield to the core at the tip. I could just get test lead ends and a stereo RCA patch cord cutting off one end, soldering them onto the test leads. Then install a female RCA connector into the case and be sure to run the 100ma high current through the outer shields. At that point one could run the audio cable core out with banana plugs to use with an external DVM or install in the case one of those cheap E-bay 200mv panel voltage meters into the case.
I dont see why not and yes just a poundshop RCA cable will make a cheap screened lead.
Didn't you write articles for Television mag?
Yep , thats me .
I don't really miss the game now, I got out in the late 90s, did university, ended up in data and telecoms, but approaching 60, I'm enjoying playing about with electronics again.
@@simontopley4771 The decline of TV repairs started when we went digital , you wouldn't miss it now , its all board replacement ,hardly any component level fault finding as there are no service manuals anymore .
Awesome, with important details.
Many thanks for that, glad you liked it.
Awesome! Thank you so much!
a very useful tool .
@@michaeldranfield7140 Indeed
Thank you Michael :) I’ll be making one of those.
Very useful item and won't take long to make.!
One can put a link in the video description tho :)
gracias señor
Many Thanks for watching.
Why two 51ohm resistors? That's 25.5ohm. Why not two 50ohm resistors?
Your Kelvin clips aren't exactly right. The two leads should each occupy a separate side of the clips, not come into the same side as you have shown. I love the proto build, very clean!
many thanks for that .
WooHoo, I just asked about this in another video.
That's not really what Kelvin probes are or how they work. Nifty instrument though!
Creative video, thanks for sharing, like it :)
No problem, many thanks for watching.
Help me understand something... if a cheapo meter costs $40, why in the world would a meter with 4 terminals to cancel out the resistance cost hundreds? I was blown away by the simplicity of the circuit and I just don't understand the price jump....
That's a good question and I don't have an answer but isn't most professional test equipment expensive to buy, unless it comes from China of course.
You can get an Nktech Vici VC480C+ milliohm meter for less than £90. A much more reasonable price. The "Learn Electornics" channel did a review on it.
You CAN build/sell a far higher precision and accuracy meter for hundreds... whether a particular one is actually built for superior specifications or just has some historical price markup that chumps will pay, well depends.
Actually, the current leads and the voltage leads can’t touch each other at the device being measured. They should be close together, but not touching.
Sure they can. Electrically it's basically equivalent. The closer the touch point to the real resistance path desired to measure the better, although you start to get diminishing returns. Probably slightly better kelvin clips could be made by having each wire go to an opposing side of the clip so they only touch when it gets full grip on something.
As pointed out in the video, if you're making a micro-ohm meter the distinction probably matters, but for the as-designed milli-ohm meter, not really.
@@ivolol If any of the 4 wires or jaws touch each other, you no longer have Kelvin clips. Close maybe, but not quite..
Thank you!
No problem at all , many thanks for watching .
Yeah I have to have one
Many thanks for watching.
Thanks so much for posting this. Could you just confirm that the 'Panel Meter' you mention should be a Voltage meter with a Measurement Range: 0 ~ 200mV DC? You said 'resolution' rather than measurement range. This is the only bit that confused me.
Sorry but all my videos contain mistakes, yes the led panel meter is 0 to 200 MV.
@@michaeldranfield7140 Thank you Michael.
Many thanks
No problem , many thanks for watching .
Brilliant
Many thanks for watching.
If just finding relative resistance, wouldn't a constant current source (cc of bench psu) and dmm be sufficient? For absolute readings, use a precision resistance calibration sample.
Much more convenient to have just one box than several different items to do the same job.
If you apply some current, less than the normal consumption, to the power supply side (3v3, 5v etc) you can use the millivolt range of a good multimeter to do exactly the same.. The voltage at the short circuit is the lowest. Before the short there is a drop in voltage. Further away behind the short the voltage stays the same.
I just found it convenient to have an all in one tester rather than using a separate meter, but as you and others have said there is more ways to do the same job.
Thank you
No problem , many thanks for watching .