DMM Continuity Tester V1.2 - Better than clicking probes together! - Page 1
Forum section: electronics / projects

author: IanJ
author_rank: Unknown
timestamp: March 31, 2022, 04:15:29 pm
content: Hi all,Watching various YouTube videos where Multimeter reviewers reach the stage where they test the continuity beep mode of the meter by 'clicking' the probes together as fast as they can to see if they can beat the 'beep' into submission.....I thought "there must be a better way than that".Not to mention I was moving from Altium CircuitStudio to KiCad V6 and so needed a quick first KiCad project to test the workflow........the DMM Continuity Tester was born.It's operation is kinda self-explanatory, but there are a couple folks out there I have pushed units out to given I had built up 3 or 4 so I guess YT videos will appear if indeed it's found to be useful.I've made the design freely available (non-commercial use only), it's based around an Arduino Pro Mini (5V) a small Zoltech LCDThe files (updated 25/06/25) are availablehttps://www.ianjohnston.com/index.php/projects/124-project-062-dmmcontinuity:The performance of some DMM's are quite surprising, here's a few:Example MARK Examples (minimum) at 250ms SPACE:- Brymen BM257 = 38ms- Fluke 85 III = 0.9ms- Fluke 87 = 0.9ms- Agilent 34405A = 25ms- Keysight 34461A - 1ms (needs Space = 300ms)- Agilent 34401A = 20ms, but will work lower but gives continious tone- Brymen BM786 = Better than 0.01ms- V&A VA38 = 0.1ms (beep varies in volume to point it's hardly audible though, obviously not using a fixed beep length)Only one meter (BM786) beat the minimum that can be set with the tester, I guess I should re-write the code using interrupts to try and squeeze a few more uS from it.EEVblog Mailbag Youtube video (featuring the DMM Cont. Tester):https://youtu.be/Xfs0dglIVOM?t=1275EEVblog Fluke Multimeter test (featuring the DMM Cont. Tester):https://youtu.be/UER8fiI9WrY?t=1190EDIT 26/06/25 - V1.2 photos attached.Ian.

author: tooki
author_rank: Super Contributor
timestamp: March 31, 2022, 04:53:11 pm
content: Very interesting!Are you able to set the resistance value? Continuity testers vary significantly in their responsiveness at different resistances. (Fluke is excellent not only for being fast, but for being fast at the resistance caused by cheap test leads. Many meters suck with cheap probes, but do well with good probes.)

author: IanJ
author_rank: Unknown
timestamp: March 31, 2022, 04:59:08 pm
content: Quote from: tooki on March 31, 2022, 04:53:11 pmIt's a rather simple circuit, a p-type FET basically shorts the DMM as it would if you were clicking the probes together. RDS(on) with the FET I happened to use is about 1ohm.Ian.

author: tooki
author_rank: Super Contributor
timestamp: March 31, 2022, 05:09:19 pm
content: Well that’s the thing, when touching probes lightly, they’re often significantly above 1 ohm. Likewaymore. The situations where really fast continuity is most useful (like when dragging across a row of connector pins to find what’s connected to what) are often those where you’re not ensuring good contact, and thus reacting quickly to, say, 20 ohms is important.Oh yeah, what would also be really interesting is to be able to test intermittent connections, that is, how does the meter respond to briefgapsin continuity. IIRC, the Flukes not only latch on continuity, but on discontinuity, ensuring an audible gap in the beep.

author: IanJ
author_rank: Unknown
timestamp: March 31, 2022, 05:20:50 pm
content: Quote from: tooki on March 31, 2022, 05:09:19 pmWell, it's open source so I guess it would be interesting to see anyone else add a few more FET's each with their own series resistor for example, or add more functions to the software like adding gaps in the continuity like you said or even randomizing the output. I guess there's lots that can be done.......just as long as I don't see reviewers clicking DMM probes together by hand and calling a DMM a pass or fail....LOL!Ian.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 31, 2022, 06:27:17 pm
content: One could just add a series resistor to the circuit. So no change needed to the tester.As long as the contact time is shorter than some 10 ms, I would not even care. So the 0.01 ms steps are well good enough.

author: Haenk
author_rank: Super Contributor
timestamp: March 31, 2022, 06:58:53 pm
content: Quote from: tooki on March 31, 2022, 05:09:19 pmI'm happy with my Probemaster probes, with gold plated tips, they make really good contact, way better than those standard probes.They make a perfect birthday gift

author: thm_w
author_rank: Super Contributor
timestamp: March 31, 2022, 09:06:59 pm
content: Smart.Do we care about delay as well? Could have a microphone to detect the beep and display delay from activation -> beep.But maybe its not an issue, and the most important thing is what you've measured here (minimum pulse width).

author: inse
author_rank: Super Contributor
timestamp: April 02, 2022, 07:44:59 am
content: A very specific piece of test equipment test equipment that you have designed there.The task could also be accomplished with a much more versatile function generator and a MOSFET.For example my very low cost feeltech generator is able to produce pulses with the required parameters.My results:Keithley 2000: 3msFluke 75III: 130msPeakTech 3720: 150msFor other continuity testers its hard to determine whether it is a click or a beep.

author: pstimpel
author_rank: Contributor
timestamp: April 03, 2022, 03:07:12 pm
content: Ian, is there a special reason for the use of exactly this P-Mosfet? Or asked different: what of its properties are key to success in this circuit / for this purpose?BR,Peter

author: Kleinstein
author_rank: Super Contributor
timestamp: April 03, 2022, 04:02:16 pm
content: The FET to make the connection should not be critical at all. Not sure why he used the extra p-mosfet. The n-FET MOSFET to drive the gate should do as well.The ROn shoud be resonable low to be safely detected as a short - so like < 20 ohms or so.

author: tooki
author_rank: Super Contributor
timestamp: April 03, 2022, 07:33:02 pm
content: Quote from: Haenk on March 31, 2022, 06:58:53 pmThey’re my favorite probes, too. But that isn’t the point:1. Any idiot can design a continuity tester that reacts well with Probe Master probes shorted against each other. It takes more skill to design one that works well with more ordinary probes, or ones that are dirty due to field use.2. In real life, we aren’t testing the continuity of our probes, but of some other connection. And that may be very oxidized.3. In fact, we might not be using probes at all. We might be using alligator clips, connectors, etc.4. In the wild, I might not be able to use my Probe Master probes. Like at work, where I’ll be using what they have.

author: IanJ
author_rank: Unknown
timestamp: April 03, 2022, 07:54:01 pm
content: Quote from: pstimpel on April 03, 2022, 03:07:12 pmIt's just a mosfet i had in stock and use on other products like my PDVS2mini. It's RDS(on) is 1ohm approx.In this design there is no high Vgs voltages to worry about that might negate some mosfets.Ps. Even if that was the case an additional 15v zener and a 10k resistor would sort that out anyways.Ian.

author: IanJ
author_rank: Unknown
timestamp: April 03, 2022, 07:58:35 pm
content: Next version if I get the time.....- Add a microphone to measure response time of DMM's.- Increase the speed so the likes of the BM786 or other fast DMM's can be measured (possibly use 16bit PWM or perhaps an STM32).- Add some arbitary type modes, i.e. mimic running along 10pins of a connector.- Add more output FETs with various different series resistances to mimic crap probes versus quality etc.- Anything else!Ian.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 04, 2022, 12:57:30 am
content: Might it be possible to implement variable resistance by operating the MOSFET as a linear device rather than a switch? Might not be the most accurate (unless you add a feature for self calibration?) but I'm not sure if there's much value in accuracy for this application.

author: IanJ
author_rank: Unknown
timestamp: April 04, 2022, 07:09:40 am
content: Quote from: NiHaoMike on April 04, 2022, 12:57:30 amMight be possible but I guess a bit of a pain to implement reliably or without getting more complex. Doesn't help matters that the voltage across DMM probes when open vary quite a bit across different models/brands in my testing.Ian.

author: Mike G
author_rank: Regular Contributor
timestamp: April 04, 2022, 01:22:02 pm
content: Nice idea Ian, tapping the probes together never struck me as a definitive way of judging the response of a DMMI have now got it running on a Grove Beginner Kit with oled display, must admit a nice bit of codingI noticed a timing glitch in the spaces but disabling the on board led flashing appears to have eliminated this, otherwise quite usefully accurate.Another option is to use the BB3 and a couple of FETs, gives an equally accurate output.Mike GP.S. looking forward to Pt3 of the Keithley repair

author: Bud
author_rank: Super Contributor
timestamp: April 04, 2022, 02:36:25 pm
content: Quote from: Haenk on March 31, 2022, 06:58:53 pmSorry, what is the point to have gold plated tips? A few hard presses on oxidized solder joints and gold will be gone from the pointy tip surface.

author: tunk
author_rank: Super Contributor
timestamp: April 04, 2022, 02:54:28 pm
content: A short youtube test by DefPom:https://youtu.be/CgyCS5RizwE?t=240

author: IanJ
author_rank: Unknown
timestamp: April 04, 2022, 03:36:50 pm
content: Quote from: Mike G on April 04, 2022, 01:22:02 pmNice catch on the on-board LED. I'll try that myself.Implementing PWM etc would of course sort out any timing issues allowing for other stuff to be done, but heck it was only V1.0.Ian.

author: tooki
author_rank: Super Contributor
timestamp: April 04, 2022, 03:42:05 pm
content: Quote from: Bud on April 04, 2022, 02:36:25 pmThat they don’t oxidize, the same reason we use gold on connectors, card edges, etc.Quote from: Bud on April 04, 2022, 02:36:25 pmDefinitely not true. My Probe Masters are at least 5 years old now and have probed many a thing, including oxidized solder joints, and the gold still looks like new. Whatever their gold alloy is, it’s hard enough to last.

author: Bud
author_rank: Super Contributor
timestamp: April 04, 2022, 10:02:48 pm
content: Still, none of multimeter brands make these. Apparently for a reason or two. Probe Master is not an industrial manufacturer.

author: tooki
author_rank: Super Contributor
timestamp: April 05, 2022, 05:37:55 pm
content: Brymen does.What, you think Probe Master is in someone’s garage or something? It may be a small company, but it’s been around for years and years and is clearly legitimate, and definitely makes thingsforserious use. They have probe extenders (CAT rated IIRC) and a lot of their older stuff was clearly focused on the telecom market, which easily qualifies as light industrial.My assumption is that cost is the primary reason gold plating isn’t universal. I’m sure it’slessdurable than chrome plating, but it’s certainly not as dinky as you claimed. (Ever seen a gold card-edge connector! Yeah, you can plug those in more than once without ruining the plating.)

author: Bud
author_rank: Super Contributor
timestamp: April 05, 2022, 06:13:56 pm
content: Quote from: tooki on April 05, 2022, 05:37:55 pmThat is exactly what i think. I recall Probe Master is a one man band. And as such i believe the guy does not make anything, just a smart person having access to internal production market in China and picking quality products for resale.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 05, 2022, 06:44:47 pm
content: Chrom plating of probe tips is more like a stupid idea. Chrom tend to build up a hard protective oxide layer quite fast.If they coat just the tip (e.g. 1mm) a gold coating would not even be that expensive.

author: tooki
author_rank: Super Contributor
timestamp: April 05, 2022, 06:45:35 pm
content: Quote from: Bud on April 05, 2022, 06:13:56 pmThey make a very big deal about their products being made in USA in their own facilities (which is why they can do things like probes with custom lead lengths on short notice). They are absolutely not a reseller of Chinese product. In fact, on their About Us page, they state that they started off reselling British-made probes, but moved to manufacturing in-house becausethatwas too unreliable.They’re definitely not a one-man shop.Edit:https://ie.globaldatabase.com/company/probe-master-incsays they’ve got 12 employees.

author: tooki
author_rank: Super Contributor
timestamp: April 05, 2022, 06:53:54 pm
content: Quote from: Kleinstein on April 05, 2022, 06:44:47 pmWhich is probably precisely why some cheap meters’ continuity (using the included probes) improves dramatically after lightly sanding the probe tips!!I just checked, and Fluke/Pomona, Hirschmann, Stäubli, and Mueller Electric all use nickel plated brass on most of their probes. (Stainless steel is an option.)(Probe Master is gold plated stainless steel.)Quote from: Kleinstein on April 05, 2022, 06:44:47 pmThe material certainly isn’t. But I’d think that selective gold would add a lot of labor cost.

author: bdunham7
author_rank: Super Contributor
timestamp: April 05, 2022, 07:18:58 pm
content: Quote from: Bud on April 05, 2022, 06:13:56 pmActually it's mostly women, including management. They aren't a huge company nor are they exceptionally technically advanced, but they certainly do make many of their items in-house in the US (San Diego) and a substantial portion of their component and material sourcing is in-house, local or domestic. For example, test leads, probes and so forth are assembled in-house but their differential probes are rebranded Sapphire just like everyone else. And I'm sure accessories and the rest of their line is a mixed bag in that regard.b/t/w, the gold plating is a hard gold alloy and is generally fairly durable, at least since they increased the thickness of it a number of years ago. The standard fixed probe is gold-plated stainless steel so it stays pointy and although I'm sure you might see wear right at the point under a microscope, I haven't noticed that it matters. The spring tips are gold-plated CuBe with a gold-plated sleeve.

author: 705jas
author_rank: Contributor
timestamp: June 21, 2022, 05:49:47 am
content: Hi AllA newbie question I suppose but having built the hardware I assumed the programming of the ProMini would be a slam dunk :-( All I get when trying to compile is errors about TimedAction.h no such file or directory. It does not seem to matter where I put the .h file in the file structure. Any ideas? thanks

author: Monkeh
author_rank: Super Contributor
timestamp: June 21, 2022, 06:01:57 am
content: Quote from: tooki on April 05, 2022, 06:45:35 pmWe birthed Lucas, the Prince of Darkness. What did they expect?!

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 21, 2022, 12:13:46 pm
content: But what does it measure?mS is milli Siemens, which also is a kilo Ohm, but the rest of the article seems to hint at some form of time duration?

author: tooki
author_rank: Super Contributor
timestamp: June 21, 2022, 01:01:16 pm
content: Quote from: Doctorandus_P on June 21, 2022, 12:13:46 pmDo youactuallynot understand, or are you just being sarcastic?The device measures the reaction time of a meter’s continuity function. So he means milliseconds, which he just abbreviated incorrectly.P.S. The siemens unit’s name is not capitalized. So the word you were looking for is a millisiemens. Same with the ohm, by the way.

author: 705jas
author_rank: Contributor
timestamp: August 14, 2022, 11:41:25 am
content: Hi AllMany thanks to Ian Johnston for the help in getting this up and running. Ian sent me the Hex file which solved the programming issue! This is now noted on his site as an option with the Hex file also linked there.All else worked as expected. A very neat little project.cheers...Allan

author: slavoy
author_rank: Regular Contributor
timestamp: June 24, 2023, 01:47:33 pm
content: Thank you, Ian, for your work. I needed such equipment (until now, I have been using a PWM generator with a MOSFET connected to probes for testing continuity). I've just ordered the PCBs. If everything goes well, next month there will be a video about this device on my YouTube channel, and it will be a regular feature in my future multimeter tests

author: IanJ
author_rank: Unknown
timestamp: June 24, 2023, 03:22:13 pm
content: Hi all,I have added a link to the HEX file to Post #1 as some folks have been having problems compiling the Arduino source code.Should be Version 1.1Ian.

author: Qmavam
author_rank: Regular Contributor
timestamp: June 25, 2023, 12:58:25 pm
content: Quote from: tooki on April 05, 2022, 05:37:55 pmI think the probes I got with my BM235 were manufactured improperly, I was having a problem getting the ohms to get near zero, often 5 to 11 Ωs. I looked over the tips and found most of the gold was gone. I posted about this before and no one else seemed to have the problem. I'm just a home hobbyist, they didn't get daily use, I did nothing unusual to cause the gold to come off, it was just extremely thin. I did buy the Probe Master probes and it fixed my low ohm problem. I have attached a picture, you can see spots of gold, but a lot of area missing gold.I'll ask again, anyone notice the gold on their Bryman probes failing?

author: RAPo
author_rank: Super Contributor
timestamp: June 25, 2023, 01:15:18 pm
content: Quote from: Qmavam on June 25, 2023, 12:58:25 pmnot in my BM257s, BM789,BM869s.

author: IanJ
author_rank: Unknown
timestamp: June 25, 2023, 04:48:01 pm
content: Quote from: Qmavam on June 25, 2023, 12:58:25 pmThose probes look like they've had a lifetime of croc clips attached to them this wearing down the coating. Wierd!Ian.

author: slavoy
author_rank: Regular Contributor
timestamp: June 30, 2023, 06:21:14 pm
content: I'm considering adding a fully automatic buzzer response measurement function to it, using a microphone, for a set of specified frequency and pulse width parameters, as well as measuring the latch time. It's been a while since I've used Arduino, but I don't think it should be particularly difficult.

author: swalayan
author_rank: Newbie
timestamp: July 29, 2025, 05:14:12 am
content: Thanks Ian Johnston, its fun project and work great. i'm using AO3402 & AO3401 mosfet because that i have in hand, no problem at all. need a little bit tweak in code so i can use 16x2 lcd display.my zoyi zt703s start beep at 1.5ms but give stable beep without skip at 80ms

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 30, 2025, 05:04:06 pm
content: For DMM probes I use 2mm banana plugs from Hirschmann. I drilled holes in the ends and then soldered the tips of hardened steel needles in them. These are by far the best probe I have ever used. I never want to go back to those those 10cm long broom handles for probing, unless mains voltage is involved.I have also clamped a small section of bicycle inner tube in between my DMM and it's rubber holster. This forms a rubber flap and I always have a few 2mm crocodile clamps clamped to them, so they are always within reach. I did this as a test long ago, and I did not have silicone insulated wire at hand at that moment. The stiff PVC wire is definitely not ideal, but apparently it did not bother me enough to fix it. I also added some heat shrink tubes at the ends for bending stress relief and I've been using these probes for quite a few years now.