How to convert multimeter into high precision milliohmmeter

Using LM317 IC, make a multimeter into a high precision milliohmmeter step by step. The accuracy up to 0.1mΩ.
Material List:
LM317 x 1
20Ω resistor x 1
100Ω variable resistor x 1
2.2uF capacitor x 1
DC socket x 1
binding post(2P) x 1
LCR clamp x 2
Hope you like it.
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[@troubleshooter1975]

Just noticed: I would strongly recommend adding a resistor in series with the pot (to limit max setting), for safety. Without it, if you build this, and don't know or you have the pot set to the minimum by accident, it will FRY the pot, and may BLOW out your meter (usually the meter amp range fuse). An 18Ω or 20Ω would do; but not more than 33Ω. A 33Ω would limit max setting to ~104mA or lower, with 5% (or 10%) resistors, you might not be able get 100mA output with the pot cranked, depending... Below 18Ω will not eliminate the potential overload condition: 18Ω is the minimum 'IF' the pot is a 100Ω 1/2W {500mW) potentiometer. Any lower and it will overload the pot at certain settings (too much current through the pot). Or, as in this case of NO series 'safety' resistor (as in this design), if the pot is set less than 18Ω, then the pot AND the circuit will overload... 100mA is used for this type of project simply because it makes the math easy: 'mV reading X 10 IS your mΩ reading' You could use any fixed mA setting, but then you would need a calculator to decipher any of your readings... Many other combinations of pot and resistor values can be used for this circuit: The pot and 20Ω resistor is simply creating a precise 12.5Ω resistor between pin 1 & 2 of the LM317 (adjustable for exact calibration). [The pot is at about 33.3Ω at the calibrated 100mA output]. You could use a fixed 12.5Ω precision resistor. You could also use a fixed 33Ω in parallel with the 20Ω resistor (and no pot). A 15Ω fixed resistor (instead of 20Ω) and a pot (or fixed resistor) tuned to around 75Ω also does the same. (and twice as fine adjustment. Although a 100Ω 25 turn pot is plenty fine, as in this (his) design... ANY* combination that gives you 12.5Ω total to the IC will work... *[don't exceed 42Ω in place of the 20Ω or this pot (if using a 100Ω 1/2W pot) will be carrying too much current]. Mr K L

[@kgsalvage6306]

What is the current needed on the supply?

[@great296]

It seems that you are an expert in electronics. May we request from you to make one project similar to this, which is more precise and accurate and put it also in youtube so that many newbies like me could make one for our personal use. Thank you.

[@troubleshooter1975]

@@great296 I wish I could. I simply don't have the time or resources to do so... Thank, I do appreciate the compliment! I usually end up commenting on videos when I am searching for specific info for something else. And I come across something that is incorrect, or something that would be a hazard, etc; I post a friendly comment or correction. I am actually trying to design an simple tester for testing snubber diodes in circuit (across a coil). I'm looking for an elegant solution, so in can run on one dry-cell. But I am leaning towards a rechargeable lithium cell. I usually don't 'build' anything; I just throw something together, and run some math in my head, and get my readings: I usually just grab some resistors and use my bench supply and a DVM to give me a measured 100mA or 1A, depending on what I am measuring, and read the drop on the DUT... [DUT i Device Under Test] [I actually have a concept for measuring junction temperature of a power transistor under test, but I do not have any time to pursue it...] Mr K L

[@pault6533]

I agree with this. I used a 47 ohm and 20 ohm resistor in || , both 2 watt for stable resistance under load. Then I added a 100 ohm pot in series with a 82 ohm 1/4 watt resistor as an additional || element for trimming. In the end I achieved a 96.0 to 104.6 mA range of fine adjustment (considering actual values of R and my LM317T). The current is rock solid! I actually built this circuit into a cheapie DMM that had lots of space inside for a lithium flat cell and powerbank chip to supply 5V while leaving the 9V battery installed. The current wires go out the disabled 10A terminal hole to a 2P connector. All I have to do is connect my custom kelvin probes to the input jacks, 2P connector, set the unit to 200mVDC and ignore the decimal place. Disconnect the 2P connector for all other functions except 10A of course. A portable solution! Note that this setup is only capable of measuring about 15 ohms max. This has to do with the voltage difference the LM317 can maintain. Ironically after you build your first module, you can use it to set your exact 12.5 ohm resistance for the second one. Thanks to everyone for their contributions.

[@jimw7916]

hes got one in parrallel

[@radamanthys847]

Tks!!!! I make this milliohmmeter and is very accurate! I mensure 0.035R with precision! Very simple project! Very good.

[@ricardomardi]

Hi Lau, thank you for your great video! VERY VERY HELPFUL. Thanks!

[@igorrizvic6008]

This is a good representation of a pcb that is good for smd components.....I mean for testing them...Just an awesome device....thanks for the video..

[@qzorn4440]

a wonderful, simple, and very accurate miili-ohm tester. 🙂 thanks. 🥳🍀🍵🚀

[@keithking1985]

Iv made this before from you channel. Thank you 👍🇮🇪💚🙏🏼

[@Appregator]

Thanks Lau. You had a great idea.

[@machyuddinmizwan722]

It really works, thank you, 👍 can't wait to your more next posting

[@user-pw8iu3gx6g]

Itswhatiwaslookingfor.thankyou .thankyou

[@huiwijaya]

lumayan .. saya menggunakan Resistor 15 Ohm dan Multiturn trimmer resistor 1K .. hasilnya tetap sama memuaskan..

[@memofernandez6488]

Como ajustas el circuito solo con las punzas separadas o usas una resistencia en serie

[@rakib.1990]

really it's working.... 💓💓💓

[@luislopez-pf5fi]

like, saludos desde argentina

[@Mohamed-jn4yr]

Tks a lot 👍🌷

[@Wilson84KS]

Nice clean work, interesting things, very good recording quality, deserves a subscription. Go big, brother 👍

[@CreativeLau]

Thank you for your support. I will keep going and share more idea.

[@hassanalijah8636]

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[@keanulance9566]

@Hassan Alijah Instablaster ;)

[@hassanalijah8636]

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[@hassanalijah8636]

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[@cloudart4070]

can I check laptop motherboard short circuit test in this device. milliohm meter probe converter

[@svsv9]

Can I adjust the trimer to get 2.5 mA? with this circuit?, I need this to be 4V output and 2.5mA limited.

[@jamesallen6007]

Thanks.🇬🇧👍

[@ZulhamS]

thank you,,,,,

[@hichamtassi1753]

Hello i created it it is nice but after some uses it got out of range and i had to adjust it again to 100mA. Is this normal ? Thanks.

[@JTelecom]

SHOW DE BOLA

[@user-yb4dz7pl2h]

lm317 is not that stable as a CC source. Unfortunately most CC sources are quite complex, requiring multiple components. One choice is to use an LM334 in the temperature compensated configuration shown. However, for its simplicity, this circuit is still quite good

[@hermandebruin1334]

Hallo can someone please help me to understand. Do you get firefox addon to translated

[@technology520]

Hello I made the Lm317 circuit. But the current is not stable at 100ma. The current fluctuates up and down. Why is this happening?

[@muhammedsons2675]

Try not to use a transformer as power supply use a stable DC power supply

[@shopehome1700]

Sir we can connect 3v cell

[@seyedmarashi]

description says 22uf Cap, Schematic says 2.2uf and video says tantalum 225 help which one is correct? thanks for nice video

[@CreativeLau]

2.2uf and 225 is correct. Sorry for the inconvenience of misunderstanding. I have amended the description. Thank you for your careful checking.

[@claudetrem01]

INTERESTING IT WILL BE CONVENIENT TO DO THE ENGLISH VERSION AS PROPOSED BY OH! Ouuch!! you have very acurate video and the way you show all the parts

[@CreativeLau]

Thank you. I will speak in English in my video later.

[@christianmorele8736]

Quelle est la valeur max de la mesure ?

[@bahmangholami3849]

Hi . Can the esr of the capacitor be tested with this circuit?

[@Appregator]

No, with ESR you need to send a small square wave into the capacitor, which effectively shorts out the impedance of the capacitor with its resistor in series and the voltage measured will be caused by the pulses produced by the Series Resistance. Maybe you can do something like switching the output of the probe with a 555, but you'll have to figure out what your multi meter will receive back.

[@kgsalvage6306]

I'm not sure why but I have it set to 100ma and I can't get it to zero on mv with the probes shorted. I get around 25mv.

[@kgsalvage6306]

I figured out my error.

[@troubleshooter1975]

Those are 'Kelvin clips'. He forgot to put them in the materials list. They are the key to accurate measurement of the DUT (Device Under Test). Without them, you could get false readings because of the milliohms of the clip connections to the DUT. DYI work-around is to use separate alligator leads to supply the test current, and to read the voltage drop. Just be sure the clips are independently contacting the DUT and absolutely DON'T touch each other! Or you can just put alligator clips on the current source, and just use the meter probes to read the voltage - Just make sure you ONLY touch the part/part's leads, and do not touch the supply clips at all. [It will not damage anything if they touch, you will just get a false reading while they are touching each other]. They Kelvin clips are optional if you just insure you have 4 independent contact points, two per each 'side'. The Kelvin clips are more of a convenience than a necessity... Also, if you measure a very low resistance resistor with wire leads, you will probably want to measure at about the estimated installed length of the leads... Remember, the leads themselves have some resistance. [clip the 'current input' leads to the point at which it will be soldered when installed, and probe the voltage anywhere outboard of that. 24ga wire has ~26mΩ per foot. That would be ~5mΩ if a part has two 1" leads when you measure it]. Insignificant if you're measuring say a 0.22Ω emitter resistor, but important if you are doing something around 50mΩ or less; calibrating instruments; or testing the accuracy of your tester. Keep this in mind if you for instance, chassis mount 'eared' power resistors (which should be greased and mounted to meet the marked power rating!), that you allow for the lead resistance from your board/chassis to the resistors... [For example, a 0.22Ω resistor mounted 6" away with 24ga hookup wire would present over 0.24Ω overall, and with 12" leads would read over 0.27Ω] Mr K L

[@dpsoni6734]

Micro ohm check kaise Karen.

[@kgsalvage6306]

What is the current needed for the supply?

[@jankomuzykant1844]

100 mA

[@Dziamero]

How do you connect two pair of clamps into one multimeter...😃...maybe via Bluetooth?

[@DhruvInvention]

I am form india I didn't understand the language but I like the video most . Can you tell me which language in the video so I can translate it .

[@toothpick5779]

Subtitles are in English now. You can translate from English hope this helps

[@blg53]

I don't understand, how can you make a constant current source based on LM317? You can set up an output voltage, but the current will fluctuate in responce to the temperature changes, oxidation in contacts and the value of the resistor to be measured. I can see it as a probe (a short circuit yes/no tester) rather than an accurate miniresistence meter. It will of course show some value in the resistance, but I don't believe you can trust it. To achieve a genuine constant current you will have to complicate the circuit somewhat. I can't see it done without a comparator (OPAMP) which together with a reference device and a high accuracy setting resistor forcing the current into total stability.

[@jasonudall8614]

Simply put Input on input in In constant voltage mode ground adj pin through resistance to ground with resistor to output pin forming potential divider...the lm317 will"try" to keep 1.25 volts between output pin and adjust pin thus setting output voltage. Now in constant current "mode" Power in on input pin Resistor between output pin and adjust pin...NO GROUND CONNECTION AT REGULATOR..just a resistor between those two pins...output current is taken from adjust pin. Current is 1.25V / ( that resistor) So with 1 ohm..1.25A constant current More conservatively 12.5 ohm would give 0.1 A

[@blg53]

@@jasonudall8614 Cheers, makes sense. I presume the stability of the current depends on the quality and thermal resistance of the internal 1.25V Zener inside LM317.

[@jasonudall8614]

@@blg53 indeed it does...but these monolithic regs. Are widely used and trusted

[@techrippon8102]

Please add English subtitle..

[@keithking1985]

i just watched this video and it has subtitles in English. just turn on "CAPTIONS", its next to the settings option icon on the video!! hope this helps you. : )

[@techrippon8102]

keith king Thank you sooooo much 👍

[@hullinstruments]

Thank you so much! What a wonderful video!

[@Robert-hr6sh]

Can't read the English subtitles even when phone screen is magnified. Wish this video was in English, would be a needed circuit.

[@pagepro211]

could you redo this video to an English version pls.

[@ivolol]

The subtitles are easily readable

[@pagepro211]

@@ivolol thanks!

[@ohouuch1333]

중국어 자막을 영상에 넣지말고, 유투브 자막으로 등록하시면 좋을것 같습니다. 한자는 너무 힘들어요..

[@CreativeLau]

Thank you for your suggestion. I will try to add english sub for each video later.

[@mdshahabuddinsabri7981]

English subtitles please

[@toothpick5779]

They’re there now

[@hyperhektor7733]

ah man cant watch it when people use sharp screw to point (and scratch) display of equiment. Its totally unessesary and a bad habbit.

[@vladb5748]

Da

[@rynax009]

万用表都不支持4线测量，何用开尔文夹子啊

[@warplanner8852]

..that's easy for you to say!

[@useruiiijjjjhhhhh]

English please

[@multiforc271]

you should have mentioned that video is not in english ! when the title is in engglish, without mentioning the language of video, it is missleading..... video disliked..... i spared you the report since i was really interested and i value those who share their knowledge. please consider mentioning the language of video !

[@Apocalypse033]

garbage！