Easy milliohm meter Project : Locate a short cicuit even if it's in parallel with other components.

[@bharwanasial]

I have made similar device by just salvaging the old ATX power supply connector, pulled out its 2 pins and put them on the probes of my multimeter. They fit well on the probes, soldered their other ends to an AA battery. Now i can use millivolt scale to find these shorts. Although its reading should not be accurate/calibrated but it distinctly isolates the shorted component on a common rail.

[@richardlangner]

That sounds like a very simple solution.Keep up the good work!

[@neeleshrana4719]

Best circuit and vere usefull. Thanks for wonderful circuit

[@richardlangner]

I'm glad it helped you.

[@fizzyade]

Hi Richard, I love stuff like this but I have a question. It's not entirely clear from this or the other video, but is there a step missing here in the video? Specifically this is because you solder to the back of the needle and therefore the resistance you're measuring will include the resistance of the needle from the solder point to the tip in the result as well, since the force and sense leads are "shorted" at the solder joint, anything from that point on it part of the measurement. I picked up a random needle and measured the resistance and it was 8.2 milliohms, so a total of (assuming they're equal) 16.4 milliohms which would need to be subtracted from the measured value. I'm interested in this since I've created a milliohmeter and I'm trying to build some probes for easy short finding (like your probes), my meter works incredibly well using traditional probes, but clearly that's not really useful when dealing with small SMT devices.

[@richardlangner]

The video showed my first attempt at the probes. I realised afterwards that I should have run the wire to the tip and soldered into the needle's eye. Ideally you should use two pins for each probe. These ideas only seem to come after the videos are made! Thanks for your feedback.

[@fizzyade]

@@richardlangner thanks for the fast reply. I have been contemplating solutions for this and like you say, there should be two pins per probe, which makes it a much more awkward problem than what it first seems, especially from a in circuit probing point of view. I have bought some pogo pins (the type you'd use for test bed probes) for this exact experiment, soldering them to a PCB (laying down rather than upright for mechanical stability and alignment) in a v-shape could allow the probe tips to be very close together but without making contact until touched onto a conductive surface.

[@richardlangner]

@@fizzyade Iv'e just looked at my pack of new sewing machine needles and a couple would be ideal for forming into a V shape with the points almost touching. I originally tried pogo pins but they don't really have the physical strength when pressed hard onto the PCB, and the resistance is inconsistant due to the sliding parts.

[@fizzyade]

@@richardlangner yeah, I was going to solder them completely to the board, such that the pig mechanism would be fixed. The small diameter of the pin and the sharpness of the point is what attracted me to them as an off the shelf solution. The other way is just to create the probes, don’t worry about the resistance and use normal kelvin probes (which you already have) to “calibrate” the probes and null the offset. I actually came across your project when I first started to think about creating a milliohmeter, they can be silly price off the shelf and I’d been meaning to buy one for years and never got around to it, I then had a short on a board and wished I had one…so hence why I’ve ended up here. I’ve created the milliohmeter, complete with 3D printed enclosure, so I’m keen to solve this last bit, so I’m definitely interested in any ideas you have, or tried.

[@richardlangner]

@@fizzyade Is there a way of sending you photos of what I have just tried with needles?

[@JorgeOliveiraDodo]

Thanks, excellent. What type/reference should we look for the Schottky diode?

[@richardlangner]

Any 1 amp (or greater) schottky diode will do such as 1N5817, 1N5818, 1N5819, or even surface mount types. Working maximum voltage must be more that 5v, which they all are! The important thing to get right is the wattage of the resistors - ensure at least 1 watt.

[@alivan6689]

Great video 👍 keep up the good work sir

[@HETRM]

How will it detect short ..can you please explain, if one of the capacitor is short ?

[@richardlangner]

If several capacitors are in parallel measure across each - the short circuit capacitor would show the lowest reading on the meter.

[@HETRM]

@@richardlangner thankyou sir!!

[@das250250]

Short in this case doesn't mean zero ohms. A short can be along any scale from ohms to micro or nano ohms . All things have resistance even when you connect two pieces of copper. What is being measured is how short is this capacitor from zero . Typically it will be milli or micro ohms scale. By moving the probes we can see where the most shorted point seems to be centred on the board

[@HETRM]

@@das250250 thanks

[@Wojkiel]

Could it be useful with diagnosing audio amplifiers?

[@richardlangner]

It could be useful if there is a short circuit which is in parallel with several components, but I would only use this in the final stages of fault-finding.

[@Wojkiel]

@@richardlangner So in what kind of elctronics this device is most useful sir?

[@richardlangner]

​@@Wojkiel You use my device when you have located the fault area but there are several possible components in parallel, and you can't easily remove each to test them. This is common in SMD components, especially ceramic capacitors which are distributed across the PCB power lines. For wire-ended components it's a simple matter to desolder a leg or two and check them so you would not need my device.

[@alexluz7023]

very nice circuit and probes... if i want to measure batteries internal resistance with this, the batteries above 5v would induce voltage back right? and if that happens so could we add 2 diodes on usb and ground to prevent it and not be concearned with polarity right?

[@richardlangner]

I assume you are joking.... (if not, please do not connect probes to any source of power)

[@janedoe6182]

No stable current source you can build? UBS voltage can differs from 5.5V to 4.5V or even more...

[@richardlangner]

You raise a valid point. The project is to locate short circuits by comparing milliohm values. If you want have accurate readings it needs to be a fixed current source (not fixed voltage) and proper 4-connection Kelvin probes. The video was to encourage perople to build something they can use, at little or no cost. And it's a bit of fun too. To answer your question, 5.5v and 4.5v are 10% out, the resistor could be 5% out, so worst case you's be 15% out, which does not really matter when you're trying to locate a short. So not accurate, but it can find the problem.

[@janedoe6182]

@@richardlangner Ah, ok. Thank you!

[@das250250]

I guess the 5 v / 50 ohms = 100mA plus zero to 0.1 ohms for the short circuit plus ohms of needles. Can we improve the measurement? : Possibly by soldering the voltage source to the very near tip of needles to reduce ohmic effect of needle. We could also use better conductive material than chrome . We can also amplify the current to the voltmeter giving it a greater sensitivity . Interesting to see how constant the current is from a 5v usb and 50ohm load is .

[@richardlangner]

Absolute accuracy is not my main concern when locating short circuits, it is the comparative resistance. I agree connecting the sense wires nearer the needle point would be better, but the twin needle contruction (in my other video) solves this issue. The main thing is that this device is easy to make and is far cheaper than a commercial product.

[@techwalainfo]

schottky diode ?

[@richardlangner]

Yes. Any 1 amp (or greater) schottky diode should work.

[@fu1r4]

Why couldn't you show us how to build it instead of a couple of pictures?

[@ivandobrev8711]

This solution is quite crude looking due to the nature of the resistors used and the power supply voltage. If accuracy is desired (which should be for this miliohm meter) a higher tolerance resitors must be used. Otherwise a current sourcing circuit must be implemented with LM317T or similar device. Nonetheless great tutorial.

[@richardlangner]

Crude, yes, and I agree with all your comments. It's really designed to find shorts to make not exact measurement. Glad you liked the video though, thank you!

[@Zava-w8i]

Can you give me the schematic

[@richardlangner]

Sure, the schematic is at time = 2:32 in the video

[@LeviBulger]

Im sure this is going to be a stupid question to ask once i hear the answer,but are you connecting the usb plug into a portable charger then probing the caps with both those leads as well as the leads from the DMM? Or are you probing the usb plug with the DMM while using the usb connected leads to probe the caps?

[@richardlangner]

Hi Levi. Not a stupid question at all. The USB part plugs into a portable charger / power pack / laptop / PC (in fact anthing that will supply 5v at 100mA or more). The two jack plugs connect to the DMM. The needle probes connect to the capacitor under test. Does that help?

[@balasubramaniant2030]

👍

[@465kuba]

Not bad idea with usb. Not very accurate but easy to made and use, dont need current mode power supply, just a power bank.

[@richardlangner]

Yes. not very accurate for measuring, but great for finding shorts.

[@mp1454]

🙏🏻🌟🌟🌟💯♥️👍🏼👍🏼👍🏼

[@y_x2]

USB will not supply 5V with this circuit!

[@richardlangner]

You are quite right, there will not be 5v at the probe terminals. To avoid turning on transistors or diodes in the circuit under test, we keep the test voltage very low. It is the current in the short circuit we are concerned with, and the voltmeter gives a comparative indication of readings. I hope this makes sense to you now.