Build A Cheap And Suprisingly Accurate MilliOhm Meter DIY Project
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- เผยแพร่เมื่อ 12 ส.ค. 2022
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This is part two of the MilliOhm Meter Project, you can find Part 1 here:
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Dual Linear Variable PSU Project
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Dual Voltage SMPS Project
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100W 220V Inverter Project
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Richard
This is part two of the MilliOhm Meter Project, you can find Part 1 here:
th-cam.com/video/rDw3oVqJHHI/w-d-xo.html
I want to build a micro ohm meter but don't know how
Note: The lower the value of the resistor - the more important it is to place the probes exactly on the same spot on the soldering legs.
This may be the explanation for the difference on the 0.05 ohm resistor value shown on the 2 meters.
Thanks for your efforts making up the video, highly appreciated
Yeah that makes a lot of sense as at these sort of resistance values, even the resistance of the component leads becomes a factor. I guess from your comment you were fairly impressed with the performance of this MilliOhm meter considering it is such an inexpensive device (though it does require the selection by hand of four resistors to get it to work well -see part one)
@@LearnElectronicsRepair Cheers - Yes - I am very impressed by the accuracy.
it just shows how far you can reach with some thinking and a handful of simple components.
@@CXensation yeah me too, and despite several previous opinions I also think the el cheapo smd tweezers converted to kelvin probes worked better that expected, though I had to strap a bit of insulating tape around them, as you may have noticed, to stop the soldered together ends coming apart again due to the tension/pressure.
Regularly use one for pairing source/emitter resistors on amps - placement/tension and DUT temperature are critical factors. Best handle with ceramic tweezers, as all it takes is to grab one with your fingertips to see the reading go up substantially - as expected with 350ppm/K.
Nicely done!
When you get down to the resolution you got down to, measuring milliohms, everything matters.
The "settling" looks a lot like thermal EMF, I would guess because the probes are made of a different material than the resistor leads, thus forming a thermocouple that introduces enough microvolts into the measurement to become visible in the readings. The value is always going down (or it could go up); showing a trend in one direction that way is a good clue. (There can be other parts of the circuit that are settling that way, of course, but thermal is *everywhere* at these levels.) One simple technique for that is to reverse the current and take a second reading, so that the EMF adds to the resistor voltage in one direction, and subtracts in the other because the voltage is negative. The "real" answer is halfway between those two readings. (This is only going to work if the circuit can handle the reading in either direction; some fussing.with the technique, or the circuit, might be required! Could be a little tricky with only one supply voltage.)
Then... doing the math for what kind of precision you're actually getting could be interesting! Computing percentage for a nice selection of resistors, and getting a good feel for what you can expect from the meter. Keep in mind the precision of the resistance measurements is entirely dependent on the precision of the current source, and the precision of the gain of the amplifier, and so on and so forth; it's going to wiggle a little bit with temperature, and time, and the weather... and maybe what we had for dinner...
I'll be trying to built this. I definitely need a 5w 10ohm r15. It was running 1.2w according to your measurement.
Thanks for the video.
For the projects listed, the inverter one is my pick. Building it might teach me to repair inverters.
I’m not sure it’s necessary, there should only be 100mA going through the 10 ohm resistor so it should dissipate 100mW I think.
A very satisfying result, Richard. Thank you to the designer of this circuit.
Yes I linked to the designers channel in part 1, it is originally published in Portuguese
I like the one with the inverter. I hope it has real sine wave output.
I'm loving your channel. I have and order in at pcbway and looking forward to building the short finder and some other projects. Thank You.
Tools for future use are always appreciated, I would very much like any "INVERTER" type projects,that has real sine wave outputs and protections,especially as I have found nothing in the English language.
The difference between the two meters could just be down to where on the resistor leads you put the probes. A typical 0.45mm resistor lead is about 1 milliohm per centimeter IIRC. I'm impressed with how well that circuit works. Makes my fairly cheap milliohmmeter look really expensive.
I was thinking the same
Curious what meter of yours that you’re referring to? Just curious is all
@@hullinstruments I have a Voltcraft r-200. It's a much nicer build quality than the vici meter but is about three times the price. It was the best I could find without getting into very expensive electrical installation testing meters, or professional level milliohm meters costing thousands.
Yeah you are the second to make this comment about where on the resistor legs i placed the probes. If there is one thing this tells me about this very cheap MilliOhm meter it's that it is extremely sensitive, far more accurate than I expected, and well worth building, on a bang for bucks scale of one to ten it has to be near the top end 😃
Yeah thinking the same, at this range and resolution you'll definitely see the varying resistances at different points of the resistor leads, pretty impressive.
Heya, love these diy bilding project you learn so much from them as specialy wen you explain the workings of them
Awesome results ! I think it would be fun to build a power supply for it, I would also like to see some cheap alternative isolated supply's for the test bench as opposed to a big transformer, great video...cheers.
I think the same - let's see what I can come up with 😉
great follow up video :)
Hello Richard! Thank You for your very usefull teaching video! It is so need heare in Ukrain Odessa! I have already buy Keiweets К601! I am very pleasure from your stuff!😊
Love your videos! I'm trying to find the project in the shared projects on PCBway but can't. All that comes up is one milliohm meter that looks completely different.
Would you have a link to this project?
You have many great DIY projects. Think I'll do the Huntron tracker also. I've been watching for a reasonably priced one for quite some time. I think one of my scopes have X,Y mode on it. Don't think my Rigol does, but one of my analog scopes surely does.
Thanks 👍
Would love to see you make a good bench power supply.
Try the one with transformers rewinding :)
Brother,
an Isolator, such as Isolating-Trans-Former, be a Need-Have for (our) Repair-Cafe.
especially when combined with some Light-Bulbs in-case-Short-Circuit.
this be a Nice-Project as a Combi ...
I totally agree - I'm gonna look at this as a side project 😉
Really nice.. how would you go about testing dual mosfets .
I’m part way through building a version of this but thenOP07s I bought from aliexpress are fakes 🤦♂️There are some good videos for how to test for a fake OP07 so at least I’ve learned something.
i was wondering if you use a 3 volt power supply and a current limiting resistor between 500 ohms to 2kohms to make the 20 cent short circuit tester. all you care about is the voltage the voltage to go down. i picked the resistor range because it a ratio of 1 to 1000 voltage drop
yes on project inverter
SIR please make a video on transmitter and receiver module of RC controlled toy car , explaining how the signal or data is transmitted from transmitter to receiver , which controls movement of the motor in the toy i.e forward and reverse movement
if i have a dc power supply is it possible to adjust the current to 0.1A and then use the DCPS as ah milliohmmeter? my powersupply has also 5 digit so it shoult work or not?
👍
18:40 - I have been unable to locate a micro ammeter on your channel. I hope you’re interested in such a project. I need to measure the current through an aqueous sample with 3.3vdc applied to the sample vial. You may very well will have been the first channel to produce such a circuit.
Where is the link to the board? I see links to everything but the Milliohm board!
Yeah the uA741 has different offset trim, and from your results not compatible with the rest of the circuit! :)
Sir is it available to purchase a ready-made one?
Don't like the open probe voltage &
IC2 has messy input circuitry .
To anyone interested in cheap/DIY troubleshooting tools and equipment… I’ll post some info below.
I been Absolutely loving your test equipment content. I haven’t really enjoyed electronics as a hobby or outside of work hours for a few years but after stumbling across your channel it’s kind of getting me back into it.
I’ve left a lot of comments on your test other vids and I’m going to copy and paste them below for anyone who wants to read them.
I have my own metrology lab and do this full-time, and I specialized in test equipment. But I also collect useful and strange test equipment ….especially devices that speed up the process of troubleshooting. I’ve got nearly 2 dozen devices in my collection that have been sold or offered as DIY designs over the last 30 or 40 years… All of them can pretty much be summed up to “short circuit tracers“… But it’s amazing how some of them go about it and some of the really neat and weird design choices. Sorry for the long comment but I’ll post a summary of my comments here below…..
Best thing I found is a “audible milliohm meter” like the EDS “ leak seeker” .....
seriously look it up if you haven’t seen one.
It’s basically an extremely fast and accurate low ohms meter that SINGS. It plays a different pitch as the resistance changes, even the tiniest changes in resistance. Like the difference in 1 mm of copper trace.
allowing you to track down shorts like nothing else you’ve ever seen. And I’ve got a metrology business doing test equipment repair and calibration… So I’ve got all the professional expensive benchtop gear… But I swear to God I grab for the EDS devices every day. Not only the leak seeker but also the cap analyzer.
Not affiliated with them at all, I’ve only talked to Dave the designer once or twice. Nothing to gain or lose and don’t give a shit if anyone checks it out… I’m recommending it only because of how much it’s helped me and countless others.
Like everything, it takes a bit of practice to get used to it. I like to compare it to a high-end Metal Detector or something like that… You can’t just spend a ton of money and expect it to work and interface with your brain instantly. Or like professional engraving equipment used by jewelers and Gunsmith. Or a fancy tattoo gun or something like that .....You can spend a few thousand dollars on an engraving machine… But you still have to learn to use it and practice.
But with a little bit of practice it will be One of the most useful tools in your arsenal.
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Also, not sure if you folks are familiar with the device called the “half ohm” available online pretty cheap. And other multimeter adapters that you can build cheap or free.
There are many videos on TH-cam about these milli-ohm adapters, I’ve tried several variations and they’re all pretty decent.
Especially if you use one of the cheap sets of kelvin clips/silicone leads available on eBay and other places in China.
Don’t get me wrong, I love my fancy benchtop equipment, with their various leads and fixtures, all beautifully and painstakingly designed…
But you can spend several hundred dollars very easily on a simple set of Agilent/keysight text leads. And unless you’re doing this work every day and offering it as a service like I am, it’s pretty much ridiculous and not needed. And you can get by with some thing that is incredibly affordable. With a precision that will surprise you!
It really is the golden age for electronics… And Especially test equipment.
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SUPER TIP…..
TLDR use TINY film thermistors that will allow you to track hotspots instantly without a thermal camera.
OK so this is a bit long I apologize…..
Yet again I’m sorry to leave another comment but when it comes to temperature detection, if you don’t want to invest in a thermal camera… Try this.
Take the smallest thermistor you can find. Like the little thin film ones found in most inkjet printers, or found monitoring the temperature in a laptop battery pack or other battery pack.
These things are tiny, They will be the tiniest little thermistors you’ve ever seen literally like The size of a large grain of sand. Like 1/4 the size of a piece of rice. The smaller the better because it has faster response and recovery since it has less mass
Get a sharpie marker and disassemble it throwing away the ink portion…. But keeping the felt tip. Poke a needle through the felt tip and position the thermistor so that The legs of the thermistor pass through the felt tip and into the body of the sharpie.
Run a few flexible silicone type wires at the back of the sharpie and connect to the thermistor. Instead of cheap multimeter leads will be OK as long as they’re flexible. You can usually get a decent set of silicone leads from Banggood for less than five dollars, keep in mind you’re cutting off the end of the probe so you don’t want to spend much money on them. Maybe even have a broken sit around and you can just step off the probes.
use a little bit of super glue or epoxy on the end of the felt tip, not completely covering the thermistor but only leaving just a tiny little portion at the end exposed.
thermistor should be pushed down to where it’s just barely sticking out, but a little bit of adhesive can protect it and make sure that it doesn’t get damaged but without covering the actual tip of it. Just so that the legs and things don’t get flexed or stressed. Because these things are tiny and just looking at them wrong and make them fall apart
Now you can plug it into your multimeter on resistance mode, and it will respond instantaneously within like 1/100 of a second to the varying temperatures. It is literally so sensitive that when I set my multimeter up in a room and leave the room letting the thermistor stabilize… If I even come a few feet from the doorway to that room you can see the multimeters display start jumping up just because of the infrared heat from 20 or 30 feet away.
It is ridiculously sensitive.
You can literally touch the wall with your hand for a split second and even several minutes later the thermistor can pick up the change in heat where your fingerprints were. It’s that crazy sensitive.
These characteristics are very similar to a thermal camera, but of course instead of seeing the difference in color you’re just seeing the multimeter resistance display jump up and down
Now that it’s plugged into your meter, that you can sweep across a circuit board and it quickly find the warmest areas.. its a Thousand times more sensitive to heat than your fingers,
this thermistor contraption is basically free, and will allow you to track down temperature differences at an incredible speed and efficiency. You can Google “thin-film thermistor“ or just rip open a rechargeable battery pack and you’ll see them taped to the 18650 cells. They’ll have a bit of kapton tape around them to keep them from flexing or stressing. I usually keep the tape on the legs but trim the very tip of the thermistor so it’s the only thing exposed.
Keep in mind the legs of the thermistor are basically like human hairs they’re so tiny.
The smaller the thermistor the quicker the response time as a bigger one would hold onto the heat and not recover instantly.
I’ve made several of these using different types and resistance thermistors. Usually the resistance is between 50k abd 150k ohms
Some recover a little faster than others depending on size, room temperature resistance, and the type of material the tip is made out of. Sometimes Glass sometimes epoxy , All kinds of different materials. I’ve had good luck with the glass tipped ones, I use a cheap diamond fingernail file to grind away the very tip of the glass getting extremely close to the junction inside of the thermistor. This improves sensitivity. But it’s honestly not even needed because they are already ridiculously sensitive
The good thing about harvesting them and using all dried up sharpie markers is there free to make. Even if you do need to buy the thermistors they’re usually a few pennies apiece or maybe a dollar. I’ve even use some of the thermistors like sold in the 3-D printing community used to monitor the hot end… They make great heat detectors for troubleshooting. And are widely available
So if you make a few with different types and resistances, some will be a bit faster responding so I’m a bit slower but that’s actually a good thing because sometimes you don’t want to respond and be super jittery.
Not only is it basically free and incredibly useful for tracing down issues on PCBs.… but you can also use it to search for “heat leaks” in your home around doors and other places that could use insulation or attention paid to the cracks
I have several thermal cameras that I use in my lab but these are just as useful, a little less convenient maybe but damn still super super useful
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Thanks for the tips.
waw, this (by far away) is the most valuable youtube comment I ever read.
thanks for being so helpful and so reasonable in your writing.
as for me I love how the expensive meters are built with attention to every detail and plentiful information of the exact performance. and I appreciate how some companies are making high precision meters for affordable prices that I can have.
It would be interesting to know why there is such a LONG settling time?
The 1k & 1uf output filter .
Great video as always richard ,
thank you for the mention :)
send me the dimensions of the Milliohm meter and i can design something and use the toy you borrowed me for it :)
spoiler( joint video with richard and me again :P)
We'll be meeting up soon.
I didn't find this circuit board on PCBway. Am I looking in the wrong place?
It's possible the original author deleted the project on PCBway. Here is the link to his video, he has links to the schematic, BOM and gerber files there th-cam.com/video/FBlCEkQsdwM/w-d-xo.html
@ 14:10 Y not use their Search Box...
Where the hdmi video?
Would my dog 🐕 play with it if i put some peanut butter 🥜 on it 🤔 😋?
If you have a laboratory power supply with current control, you can deduce the low resistances using Ohm's law:
R = U/I
with U = 5V and I = 0.1A then you multiply by 10 the result of the voltage recorded by the volmeter!!
That's all !!