Scullcom Hobby Electronics #31 - Design & Build a Milliohm Meter
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- Опубліковано 8 лип 2024
- In this project we will design and build a Milliohm Meter which is capable of measuring low resistance from 2 ohm to 0.1 milliohm with an accuracy of 0.1% or better. The unit will be easy to build and low cost.
Below are the links to the circuit diagram and the PCB artwork and layout:
www.scullcom.com/Scullcom_Mill...
www.scullcom.com/Milliohm_PCB_...
Parts List Below:
1 x LT3092 (SOT-223 case format) Programmable Current Source.
1 x LT1634 - 1.25v version Precision Shunt Regulator (SOIC Case format).
1 x INA106 - Precision Diff. Amp. (SOIC Case Format).
MAX680 - Dual Voltage Converter (DIL format).
LM2940 - 5 volt Low Drop Regulator (TO-220 format)
1 x 8 pin DIL socket.
1 x small push button on/off latching switch.
1 x 220uF 16 volt capacitor.
4 x 4.7uF tantalum capacitors.
8 x 100 ohm 0.1% resistors.
1 x 56 ohm 0.1% resistor.
1 x 10 ohm 0.1% resistor.
1 x 499 Kohm 0.1% resistor.
1 x 100 ohm 15 turn horizontal preset.
1 x 100K 15 turn horizontal preset.
6 x 4mm banana sockets
1 x battery holder for 6 x AA batteries. - Наука та технологія
A well paced lecture on how a project is developed: from the start block diagrams and their relationships, Then a purposed schematic to iron out some obvious kinks and electrical issues, to a breadboard to test the theories calculated prior, make adjustments or changes to anything outside desired specifications, fine tune, final testing, prototype and test, all with jelly bean parts...marvelous. Spot on.😊
You remind me of my old instructor, Dr Chow, wasn't so good with english but could get the job done, he would draw out three large classroom dry erase boards with circuits then explain them. This was a little tech school in Texas, only got a little AAS degree but I wish I could go back in time and learn more.
Well, I know I'm late on the comment. I wanted to tell you what a great job you did and how much I appreciate your work. Video like this are so helpful and I learned a lot from yours. I'm just glad that people like you take the time to do them.
Thank you for presenting your excellent and detailed project to us. Great professional work.
Its an absolutely pleasure to follow your teachings. Terathanks you for all! :-D
Chris Tate (commented below) raised the point about using a lower constant current source. During my initial project design I did consider using a INA131 instead of the INA106. The INA131 has a gain of x100 so you could use a 10mA current source instead of a 100mA current source. I did initially test both options but I found the INA106 easier to set up and trim the offset voltage. The wiring would also be slightly different as pin 5 on the INA131 is grounded and the reference pin is also different. The INA131 is also more expensive than the INA106. Another option would be to use a INA110 which has switchable gain options but is in a 16 pin DIL package. In the end I went for the INA106 which was very accurate and stable and worked well and was cheaper.
Amazing projects, by the way! Love this concept-to-product video format!
Thank you very much for the tutorial video. Well explained in making this professional instrument. Well done.
Thank you very much for your videos I cannot wait to build from your projects I’m a hobbyist a beginner learning went back to College to take electronics classes. Cannot wait until my grandson gets old enough so I could build some of these projects with him.
Love your channel and projects. That's the difference between (real) electronics and being just a kit assembler. Excellent! Keep up more projects coming!!!
Thank you.
Outstanding, thank you for all the details. These videos must take so much time to make! It's really appreciated.
+Lawrence Kesteloot Thank you for your kind comments.
Super work Louis, thanks for sharing your design and final build!
+Dino Papas Thanks Dino.
Thank you sir for the patience with which you explained the principle of operation directly on the diagram, and for offering a constructive version accessible to those who really need such a tool. For a long time I somehow wanted to complete my lab with something like this but now I have a template that I will definitely make.
Boys, subscribe to the channel as it deserves, not just for the way this gentleman explains, not just for the "toy" ideas you see!
Thank you again !
Those are some seriously impressive hand drawn schematics! Vastly beyond my capability.
Excellent project and a nice explanation of the circuit.
Many thanks.
I love you’re projects thank you for the efforts made into making them and explaining everything .
Great circuit design. Thank you
Really helpful video. Thank you very much! I have 2 of these recently brought in for repair, so will follow your excellent suggestions and instruction. Enjoy your very positive approach!
I love how you explain your designs from the block diagrams to the detail PCB- I will probably never need such a meter but I learnt a lot from how you designed it using the various ICs. I know for a project I will use your MAX680 design.
Glad you enjoyed it. Thanks.
Great presentation for a practical Milliohm meter.
Thanks George.
Very nice build. Loved watching this. Very thorough.
bom trabalho!! parabens!!!
Very nice explanation. Thank you so much for sharing this video.
Very interesting. Thanks for sharing
Thank you so much. Very interesting, and remarkably simple. Perfect for measuring the resistance of high current (up to 2700A) welding cables. At those currents they can heat up enough to melt the cable sheath, even with 120mm squared cable. Part of my job is to recommend what size of cable is needed for a given length, and current. Now I will be able to actually quantify the job. As you can imagine a 100 meter length of 120mm cable can cost many hundreds, even thousands of pounds.
Wonderfully built and explained with care and attention to detail .ty .
Thank you. I will be posting an update on this project soon as a PCB is now available for this project.
Very nice project. Always nice to build your own test gear.
a very interesting project Louis and great video as all your other videos and tutorials ! Been following you for years. Thank you very much !
I sincerely do hope that you and your family are doing well. It is nearly 2 years since your last video. Take care Louis. Greetings from Hamburg.
Thanks. A very detailed video
been wanting something like this for a long time but just needed someone to explain how to do it so simply. Don't have time to make right now, but will defiantly be a project in the near future!Thanks alot
+Mighty Astro Thanks for your comments.
This is a very neat and useful project. Thank you much for sharing.
Thanks for your comment.
Great project, thanks for sharing.
+William Culver Thanks.
Thanks so much for this project!
I have to test welding machines which can output up to 2700A, so knowing what your load resistance, which is usually just lots of welding cable is vital.
This will make my job calibrating so much easier
Glad you found this project useful.
Great project !
Thank you.
+Милан Младеновић Thanks.
Mr. Scullcom has created a Hobby Electronics Cult with his creative high end projects 😀 there should be a channel just for this type of culture with viewer feedback 🥳 new projects kits.
Good project worth building. Cheers
This is the third time I'm watching this video.
The interesting thing is that every time I watching I learn some thing different, I will build this project, already have most of the parts here with me.
Thanks for share your knowledge Sr.
Many thanks. Glad to hear you find it helpful. Regards, Louis
Thank you.
Excellent. Thanks
Excellent project and very well explained.
+Mark Garth Thanks Mark.
This was a great project!
+search4robfen Thanks.
This was excellent explanation and video production. I just wish I needed a milliohm meter.
Great job as always! Very instructive video. Actually it's so simple and usable that I will try to make a full smd version, just for learning purposes. Thanks for sharing...
+Piotr Hołowicz Thanks. A full SMD version should be quite neat.
A cute-looking design. I'll be attempting to build this one up, using one of Barbouri's PCBs from oshpark. One thing I note is that the 2ohm upper limit of this unit seems to be entirely due to the panel meter. I found myself a 4 1/2 digit display panel meter on eBay that goes up to 4.3V, so with any luck I'll end up with a meter with a greater range that can go to 4.3ohms instead, but still with the given accuracy and precision of the unit presented here.
Very good project.
Nice video. That is a handy low Ohms meter.
+Robert Calk Jr. Thanks Robert.
Very nice project, thank you very much for showing, and give me the possebility to build by myself.
Thanks. I will be uploading an update on this project soon using a smaller PCB and some improvements to the circuit.
Thank you for the explination, learned a lot
Glad you found it helpful.
Brilliant!
Thank you for the info on the 0-2v panel meter I have now ordered it............................Berni
Well done, sir.
🎉 he's still alive. Keep up with the channel.🤗
Hi Louis,
As usual, a very thorough attention to detail.
Another KiCad user here. I used to use Cadsoft Eagle, but switched when Eagle 5 would no longer run on the latest Linux distributions.
For front panel work, I've had pretty good luck with Librecad printing 1:1 to a laser printer, then using glue sticks to stick the paper down to the front panel (Glue stick idea comes from electronicstrivia). I then use a drill press to drill holes, and a nibbler
tool and nibble square and rectangular holes. The only downside to the nibbler is that it is tedious (and sometimes painful) to use.
+Steve Rodgers Thanks for the comments and info.
I dare to say that your content is more educational than Dave's from EEV, too bad we havent seen from you lately.
I love your videos! Great stuff :)
+Alexander Brevig Thanks Alexander.
I really cant thank you enough for your video. I learned so much. Please never stop doing these kinda videos. And if you can find more time please do more frequently. I am pretty sure a lot of people would want that. Also the main disadvantage with starting up electronics is how pricey the test gear is and the people who cant afford them or cant source them in their demographic area have no other go. But with the help of videos like yours and other youtubers a lot of people can build their own. Like someone mentioned above it would be really awesome if u can explain how each component was selected for eg: what to look for( freq response, slew rate and other characteristics) in an opamp for a project. And for the next project please build a really precise voltmeter like the one you have. Not everyone could afford a 6 1/2 multimeter in order to calibrate the circuits u have designed in other videos. It would be really cool if it had a digital autocalibration with a help of a micro :). Once again thanks a lot really appreciate your videos.
+Asniex Asniex Thanks for your comments. You must have read my mind. My next video project will be on designing and making a precision 6½ Millivolt meter with auto calibration option at low cost suitable for the hobbyist. I have been busy of late but hope to complete this video in the next few days.
That really chuckin awesome
Amazing ... Easy to understand even for a noob like me ... 👏
nice work.
Hi, very nice project, I will make this, I had the same idea but you make a very professional project !
what a great video !
Amazing!
Interesting, thank you for sharing :)
+Yann Kitson You're welcome.
Really nice project sir 👍 please make more.
Thanks.
awesome.
Well explained.
Thanks.
RIP my friend
Super, Sir.
I'm a new subscriber and a fan sir. 😘
Great!
WellDone Man, Excellent Thanks
Thanks Seyed.
Thank you for your video.How the 10 Ohm resistor compensate the 100 Ohm resistor effect ?. is there any calculations or any formula or any topic talking about this ?
Thanks sir
real perfect
Thanks.
Two things:
1. If you don't have a good multimeter, you have no way of knowing if your source is really 0.1000xxx mA.
2. 100mA is good for low resistance, but will cause an error because of heating the resistor with 0.1A
Thanks for video, as always love to watch them
+First2ner Thanks for your good comments. I have found using a good quality resistor either a 0.1 ohm or 1 ohm at 0.1% tolerance, you can use that to set the reading and that should give you 100 mA, at that tolerance level. I take your point about the 100mA with regards heating but I have found that in practice with resistances below 1 ohm it has little effect and usually you are testing a resistance for just a few seconds (for example a 0.1 ohm resistor at 100mA will only needs to dissipate 1 milli watt of power).
+First2ner This is why the resistors are in parallel. 8x 1 watt resistors in parallel is a max rating on 8 watts. 1mW requirement means it's not even an issue. Awesome
Great video !! I like the total project done in one video concept it's great for such small project. One request that please include some videos where you design this project, what do you keep in mind while designing that project and also component selection. These are some parts where noobs like me have a hard time.
Thanks for the video!!
And one more request if you can make a video on op amp stability having tons of problem there.
+Yash Kudale Thanks for your comments. Good point about the design process. Also I have been considering a video on op amps. May be something I can do when I have time.
AMAZING
+Adil Malim Thanks.
Question about the INA106... If R1 is 10k and R2 is 100k, should it not be a gain of 11? Gain = 1+(R2/R1) This is where I always fail to understand...
Very precise and detailed tutorial. So much clarified. Thank you, I learned a lot! I used this theory to construct a more accurate shunt for my DC load.
+Mike Novo Thanks for the comment. In this circuit I am using the INA106 configured as a Differential Amplifier the gain is therefore x10. We are using both the + and - inputs and therefore the output is Vout=10(Plus Input - Negative Input). If you were to configure the INA106 as a non inverting buffer then the gain would be x11 but in that case the negative input pin (pin 2) would be grounded. Hope this clarifies the point.
Of course. I see that now. Thanks!
those are nice leads!!! really nice work! I truly enjoyed that, now I have to make one! a great program for laying out panels is "Front Panel Designer" try it out (no connection to the company, just like their free software) Be Well! i love it that you use KiCad too!
+su pyrow Thanks for the tip on "Front Panel Designer".
You must have the pro edition of DaveCAD... those schematics look amazing!
Thanks :)
Nice job
Small and simple circuit
Only you should note capacitors
Of the LM2940 should be ESR of 0.1-1
Preferable tantalum
+David Az Thanks for your comments.
Those Ebay banana plugs on the red and black leads will tend to be intermittent if the spring around the outside of the center pin is loose like they usually are. I got some like that and found that I had to solder one end of the outer spring to the center pin before they would make good contact.
Thanks Steve for your valid comment. The one I use are quite good quality so they seem to have been OK so far.
Regards,
Louis
Perhaps your 4.5 digit meter has a trimmer on the back. You could fine tune the reading to match the voltage reading on the more accurate Keithley meter. I am gathering parts for this project now. I've been wanting one to track down shorts on PCBs. Thanks.
+ToltecMerc Thanks. Yes you are right their is a trimmer inside the panel meter, I will give it a try.
First of all, love your videos. Would be awesome if you made an all in one DC precision multimeter with the ohm meter, voltmeter and then add precise amp meter. Basically making a poormans Keithley 2000 multimeter. Could really use one of those :)
Thanks for the comment. Nice idea but I think it may be costly to fully copy a Keithley 2000. Regards, Louis
Question, please: wouldn't the DUT make the constant current smaller? The R to GND gets bigger with the DUT?
great stuff!! If you visit this project again perhaps a multimeter attached to the rear to show readings above 2 ohm. Its almost an ESR checker?
I can't believe how much they want for some equipment, is it that much better then say building this? This one appears to be really accurate and sensitive.
Does it measure the difference between two resistors - 1000.1 Ohm and 1000.01 Ohm ? Could it be used for selecting eg. 1k resistors?
Hi Louis, I'm trying to measure uOhms accurately (resistance of a copper bussbar) could the INA106 be directly replaced with the INA131 to get the 100x gain?, My guess accuracy would suffer....
Hi, I think you would have to make minor changes to the PCB. The INA106 Reference pin is pin1 but on the INA131 it is pin 5. Pins 1 and 8 of the INA131 should be left unconnected. Other than that all the other pin connections are the same. So I think if you make the pin connection changes to the PCB it should work. It would be interesting to see how it functions with the INA131. You would also have to take in to account change to voltage reading on meter. To maintain the same gain error as the INA106 you should use the INA131BP version. If you try it let me know how you get on. Good luck.
Great project, thanks for sharing.
Have you considered some kind of thermal EMF compensation? I guess it is perhaps not essential until you get down into the 10s of microohm.
+TheStuffMade Thanks for your comments. Thermal EMF compensation is really only needed at much lower resistance readings in the low micro ohms and below. Also if you wanted to check such low resistance readings you would also need to screen all the input leads to stop pick up of noise.
If I have a 6 & 1/2 digit panel meter or multimeter can I measure a 1micro ohm resistance with this device ? What is that limiting this circuit to measure a resistance only up to 0.1mili/100micro ohm not less than that. Please answer.
This is an excellent project. I will probably build it and use my Keithley 197A for the meter since it is the most accurate meter that I own. I see possibilities for using this for finding shorts while troubleshooting PCB's. One question that I have though. Would it be better, at least in my scenario of using this to find PCB faults, to use 10ma as a source instead of 100ma to reduce any heating? Or, do you think that this would not matter?
+capriracer351 Thanks. I have found that using 100mA current source to be the best option as you are able to get a better voltage reading and therefore a higher degree of accuracy. Some commercially available Milliohm meters on the market do use 10mA source current but in practice I have found their results to be poor on very low resistance readings below 20 milliohms. The higher the current used the better the accuracy of the results. Of course there may be some difficulties in providing a high value very accurate constant current, but today with the Linear Technology IC LT3092 this is relatively easy up to a maximum current of 200mA. At these levels heat is not really an issue. So to summaries I would recommend you stick with the 100mA.
Thanks for all of your hobby electronics tutorials!
I have a quick question. Are you building these projects with batteries solely for your portability needs, is it absolutely necessary in this design for isolation from mains, or are you using batteries just for design simplicity?
Thanks Jake for your comment. The reason I have tended to use battery operation for most of my projects is to make it easier for the hobbyist and amateur who may not feel comfortable with building mains (240V AC) power supplies and the dangers that can pose if you are not familiar with working with mains AC. All of the projects could also be powered from a mains power supply if you wish. You could either build your own or buy an off the shelf mains power pack.
I have also designed and built valve amplifiers operating from a mains power supply and high DC voltages. If there is an interest in this I could do some projects/tutorials on building valve amplifiers and point out the safety issues.
Regards,
Louis
Thanks for the reply Louis.
I've found myself building power supplies for basic experiments, mostly working with guitar amps and op amp preamplifier circuits. I have come across the limitation of my tools. Your tutorials have helped me see how I can connect the dots and fill the gap in my lab. I really appreciate how you break down exactly how each item works in the circuit and why. I feel like I can use individual elements and the underlying principles to create designs of my own.
I have very limited means, and far too much time on my hands after an accident left me disabled back in February 2014. I went from building hotrods to electronics to fill my time. I am trying to apply what I learned from autobody and engine building -buying parts is fun, but collecting the tools and skills used to make parts is the real secret to success.
I already had the basic tools like a decent multimeter and hand tools. Since getting hurt, I've been fortunate enough to pick up a second hand Rigol digital oscilloscope and a good soldering station. I also have a local thrift store that lets me pick up any broken electronics that they throw out along with the gigantic tangled mess of wires and power supplies they throw out regularly. I've collected a lot of junk so far. That gives me access to almost any jellybean components found in most consumer electronics along with any common wall wart and switch mode power supply made. This in turn forces me to learn to test everything from shunt resistors, zener diodes, capacitor ESR, and transistor curves, all of which I'm currently trying to wrap my head around. It can be time consuming to learn this way but time is one thing I have too much of.
I really do appreciate your projects and I want to build a few. Hopefully my permanent disability goes through soon, but until then I'm using the building blocks of your circuits to understand circuit function and to build a rudimentary version on my own using discrete components. I have a shopping list of parts to build your 6.5 digit millivolt meter, your milliohm meter, and I will probably try your function generator in the future as well.
I'm currently working on an adjustable dual polarity tracking power supply using a lm317 and an op amp, a discrete floating adjustable power supply with current limiting, and a simple audio probe/function generator/crystal tester using discrete components and basic op amps.
I am interested in expanding my knowledge and experience, but I don't even know what a valve amplifier is used for. I'm very linear with my learning curve. When I come across a problem I can't solve I want to understand everything related to it. For instance, my inability to measure current shunts, lead me to understanding how a 4 wire kelvin connection works, differential amplification, and a more broad understanding of the need for accurate current source circuits. I also picked up a basic understanding of wire resistance and capacitance and it's impedance matching effects, reflected waves and their measurement using a Schmitt Trigger to measure a coax length, and I even learned a bit about antennas and built my first. Some of that came from your milliohm meter tutorial, and some of that is from several other sources. I learn by exploring problems and solutions like this.
My next experiment will be to try to build a differential amplifier using transistors in a long tailed pair and see how that compares to parts of your milliohm meter circuit. I found a good tutorial on a long tailed pair from Alan on A2AEW where he explained how to build an adjustable triangle waveform generator. I will try to expand on his lesson by trying to figure out how to implement some feed back into the circuit, but this subject is on the foggy edge of my understanding and ability.
The sad thing is that I have an old 80's broken Programmable Power Supply from Fluke and one that powers up from HP. Both were given to me, and are enormous rack mounted units. I haven't been able to figure out how to interface with the HP and make it work. I much prefer analog electronics to programming at the moment. The timing of bits and everything involved to get the thing running (cheaply) is mind boggling to me, and I keep putting it off until I understand electronics better. The fluke unit, however, I can't find enough information on, as no one appears to have a full schematic. It was missing capacitors on a couple of boards but I have no way of figuring out what they were. It has lots of interesting parts including a nice precision voltage reference, a massive transformer and tons of discrete matched and precision components, but without a schematic I stare at it for hours in perplexity... One day.
Anyways, sorry if my ramblings are unwelcome. They could be considered a marker of where one odd member of your audience is in terms of understanding and ability. I'm probably in over my head with most of your content, but I have a tendency of banging my head against the wall of knowledge until I make my own doors.
Thanks, -Jake.
Hi Jake,
Looks like you are having an interesting journey learning electronics.
All the best,
Louis
Hi there is chipper method to do this if u have 3 diode in parallel and u want to know which on faulty , use power supply with limit current and put minus probe on one diode and the same time touch the diodes and u feel the shorted diode become warmer then other .simple no??
nice very nice
Thanks.
What a loverly job :-D, that must have taken a lot of care to keep errors out of the measurement, i can see that the 1.25v ref can be slightly off, its the stability that matters more.
The trim can countermand any slight error, too clever :-D.
And your set zero offset bias is ideal :-)
1000th of an ohm reading (display wise), the final digit can be ignored.
I hope you made this project for yourself and not just to teach us.
Really simple to make, simple to use, ohms law confirms it, Brilliant :-D
+zx8401ztv Thanks again for your comments. I did this project to see if I could build a milliohm meter which was more accurate than my Keithley 2000 bench meter on its low ohm ranges and I have to say the unit turned out to be much better than the Keithley. I also have a commercial milliohm meter and have found that it is also not as accurate as this project. The main reason is that in both cases they used a much lower test current - in the case of the Keithley 2000 they use a test current of just 1mA and the commercial milliohm meter I have uses a test current of 10 mA. As a bonus I found I could design and build this accurate milliohm meter at a fraction of the cost and so I thought it would be nice to share this project.
+Scullcom Hobby Electronics
Thank you very much for sharing your accurate designs.
You have an ability to design "no nonsense projects", i really enjoy the simplicity and ease of understanding them, your operational discription leaves no grey areas to confuse anyone.
Im a bit thick at times and i appreciate your teaching :-).
No need to reply :-).
+Scullcom Hobby Electronics But, the reason they use such low current is to avoid thermal drift in the resistor due to it being heated up by 100 mA. So, there's an argument to be made that your reading is more erroneous for resistors with a higher TCR rating.
+SteelBlueVision True but resistors never stay cold in equipment, so testing them cold isnt the way they will be used.
Im not saying your wrong, but resistors do get warm :-)
Your point is very valid, I was talking in isolation (i.e., on a breadboard). On the other hand, if you're after a truly accurate measurement, it is probably a good idea to apply the exact current that will be flowing through the resistor (assuming it is constant of course), or a range otherwise...
I would think that 100mA is a bit excessive for a test current. Isn't there an alternative to the INA106 with higher gain to work around this? Otherwise, a very interesting project, I've used other INA series op amps for precision current measurement before, and they've worked out great, with very little supporting circuitry
Nice tutorials and i like it then, You are a good teacher can you make a video about transformer , how it working ?
+The mad Engineer Thanks for your comments.
It's a amazing project!!
It seems to be very accurate, but I have a question, could I use it on industrial application on a motor factory, measuring the inductor resistance of the motors?
Thanks. Yes it could be used to measure low resistance of motor winding if you wish.
Great project!!! Wondering - can you really trust the panel meter?
+MrMonomonster Thanks. The panel meter I used on the project proved to be accurate up to 0.1mV reading. So it was fine what the project set out to do. This panel meters are a little more expensive than some others costing around £8, but worth it.
any reason you couldn't use a panel-mount multiturn pot for the zero trim other than cost?
Sir, can u built ESR meter to check electrolyte capacitor