BM786 continuity resistance - can it be changed and beep-level lowered? - Page 1
Forum section: electronics / testgear

author: Beauvais7165
author_rank: Contributor
timestamp: February 15, 2025, 08:32:40 pm
content: I have bought aEEVblog BM786, and I am a little puzzled about the resistance level for the continuity tester - and if it somehow can be lowered?The first few times I measured with it, I got a little "scared", as I did measure shorts, where I previously did not, but after some time I figured out, that it was due to a higher resistance level being seen as a short. In the manual it states:Audible threshold: Between 100 Ohm and 420 OhmI am not sure what my other multimeter has as resistance level, but it is much lower, and I would prefer this, as I get a lot of false-positives.Also, can the beep-level be lowered, as this is quite high?I love that it reacts so fast, and that the displays flashes, but I actually end up using my much older and slowerVelleman DVM68multimeter for continuity testing, as I trust this more.

author: J-R
author_rank: Super Contributor
timestamp: February 16, 2025, 06:32:12 am
content: There is a mention of reducing false positives with the continuity behavior by modifying the board :https://www.eevblog.com/forum/testgear/bm789-continuity-behaviour/msg5108199/#msg5108199Some of the details are a little sparse.I suppose an external modification could be to add a resistor in series with the test leads, maybe 200 Ohms? That might desensitize it enough for your purposes.The 121GW has an adjustable continuity setting, less than 30 Ohms or less than 300 Ohms. It also has a continuity break detection mode for greater than 30 Ohms or greater than 300 Ohms. Its speed is not insanely fast, but still decent.A lot of bench DMMs have a fully adjustable continuity beeper, such as the 34401A. 1-1000 Ohms. Default is 10 Ohms.

author: Beauvais7165
author_rank: Contributor
timestamp: February 16, 2025, 10:26:10 am
content: Thanks a lot for your finding, but I am not sure this is the exact hack I am searching for, as it seems more to be about reducing the "annoying behavior with the BM789 in continuity mode where, when connecting the probes to a part of a circuit where there is no continuity (or low resistance), it gives a short beep, but then stops".I am quite surprised to find this kind of behavior in a not-cheap multimeter like my BM786, and I am puzzled how it can be worse than my very old and probably cheap Velleman multimeter.

author: J-R
author_rank: Super Contributor
timestamp: February 16, 2025, 10:01:15 pm
content: Quote from: Beauvais7165 on February 16, 2025, 10:26:10 amYeah, I don't know exactly how that hack works, maybe ask in that thread for more information. But I think it could change the threshold, which is what you're wanting.Quote from: Beauvais7165 on February 16, 2025, 10:26:10 amBetter or worse is probably a matter of perspective. False positives, or false negatives??I'm not sure why Brymen consistently selects such high trigger points, but it seems to be OK for most of their fans. My BM789 is 300 Ohms, BM037 is 177 Ohms, BM235 is 165 Ohms and BM869s is 88 Ohms. I don't know what their logic is for choosing this value, but for sure they missed an opportunity by not making it selectable.Checking my other handheld DMMs, it seems a common standard from other manufacturers is right around 30 Ohms. Although my newer Flukes such as the 87V and 287 are 50 Ohms.Ultimately, a lot of people have multiple DMMs for reasons like this. There is no "perfect" DMM. Age, cost and features are not valid metrics because there is always some random use case that pops up.So just use the Velleman for this situation if it works better.The 121GW might be a decent companion to what you already have. I wouldn't trade it in for the BM786 though, since you'll just end up with a different set of flaws.If you're super serious, then get a bench DMM that focuses on this functionality (also found as a go/no-go feature).

author: Fungus
author_rank: Super Contributor
timestamp: February 17, 2025, 06:00:54 am
content: Quote from: Beauvais7165 on February 16, 2025, 10:26:10 amI really don't think this is a "cost-based" decision by the designer.

author: bdunham7
author_rank: Super Contributor
timestamp: February 17, 2025, 06:13:05 am
content: Quote from: Beauvais7165 on February 16, 2025, 10:26:10 amI'm not sure whether you're referring to your concern or the hackable one when you say "not-cheap", but those are both design choices not cost-cutting. One possible hack for your issue is to simply put a resistor of 100-200 ohms in series with one of the test leads. You'll have to experiment a bit because that 100-420 ohm spec for the threshold is pretty wide and IDK why.

author: Fungus
author_rank: Super Contributor
timestamp: February 17, 2025, 07:36:38 am
content: Quote from: bdunham7 on February 17, 2025, 06:13:05 amYep, it seemsveryhigh to me. I did a double-take when I saw it but I checked the datasheet and it's real.I'd love to know what some real-life measured values are. I can't imagine owning a meter that thinks a 220 Ohm resistor is a short. Does it at least show the measured resistance on screen?FWIW: My BM857s says "20-200 Ohms" in the manual and it beeps around 64 Ohms.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 17, 2025, 12:45:07 pm
content: Quote from: Fungus on February 17, 2025, 07:36:38 amI do publish the ones I have measured, which includes the BM786. From my limited data, Brymen do tend to set the short detection higher others.

author: Fungus
author_rank: Super Contributor
timestamp: February 17, 2025, 01:14:16 pm
content: So, yeah. It thinks a 220 Ohm resistor is a short. I feel more people should be discussing this.https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/

author: joeqsmith
author_rank: Super Contributor
timestamp: February 17, 2025, 05:43:57 pm
content: Quote from: Fungus on February 17, 2025, 01:14:16 pmFrom the OPs initial post:Quote from: Beauvais7165 on February 15, 2025, 08:32:40 pmIt seemed clear they want their meter to not indicate a short until a lower resistance value. I was surprised to see people suggesting to add series resistance as this is only going to make it worse.I've never asked Brymen why they set the threshold so high with their meters compared with other brands. I can certainly understand people not wanting it to detect anything above 50 or even lower values.

author: bdunham7
author_rank: Super Contributor
timestamp: February 17, 2025, 06:30:34 pm
content: Quote from: joeqsmith on February 17, 2025, 05:43:57 pmSuppose I have a meter that beeps at 270R or lower. I want it to beep at 50R or lower. I add a 220R resistor in series, will it not do exactly what I want?

author: joeqsmith
author_rank: Super Contributor
timestamp: February 17, 2025, 07:13:09 pm
content: Actually, I think I am thinking about it backwards...Carry on.

author: bdunham7
author_rank: Super Contributor
timestamp: February 17, 2025, 07:34:08 pm
content: Quote from: joeqsmith on February 17, 2025, 07:13:09 pmLet me guess--you got Thornton and Nevinen confused.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 17, 2025, 07:40:03 pm
content: Quote from: bdunham7 on February 17, 2025, 07:34:08 pmExactly. I transpose letters, numbers, thoughts..... Coworkers could tell stories.

author: Fungus
author_rank: Super Contributor
timestamp: February 17, 2025, 10:33:34 pm
content: Quote from: Beauvais7165 on February 15, 2025, 08:32:40 pmWhat I did: Attach a potentiometer, turn the potentiometer knob until the meter beeps, now switch to resistance mode...

author: EEVblog
author_rank: Unknown
timestamp: February 17, 2025, 10:47:39 pm
content: Quote from: Beauvais7165 on February 16, 2025, 10:26:10 amOne persons worse, is another persons better.

author: EEVblog
author_rank: Unknown
timestamp: February 17, 2025, 10:55:48 pm
content: Quote from: Fungus on February 17, 2025, 07:36:38 amYes, it shows the ohms value to 10mohm resolution.I measured one, it triggers at 270ohms coming down, and shows some hysteresis where is switches off at 290ohm ohms on the way back up.

author: J-R
author_rank: Super Contributor
timestamp: February 17, 2025, 10:58:07 pm
content: In addition to the other Brymen DMMs I tested in my previous post, I pulled out the oldest Brymen I have, the BM202 and its trigger point is 63 Ohms. Manual states: "between 20 Ohms and 150 Ohms".- Have they been increasing it over the decades?- Is there a wide variance to this value, even within a specific model, depending on the phase of the moon on the day it was manufactured?

author: danno_cj
author_rank: Contributor
timestamp: February 17, 2025, 11:55:05 pm
content: The question is still without answer. Can be done something to lower the threshold without using modified leads that affect the reading in other modes? Using two sets of leads can be annoying, one for continuity and one for general use. Where to mount the resistor inside to modify only the continuity behaviour?

author: bdunham7
author_rank: Super Contributor
timestamp: February 18, 2025, 12:55:47 am
content: Quote from: danno_cj on February 17, 2025, 11:55:05 pmThe answer was a 220-ohm resistor. You changed the question! The answer to your new question is that while we don't have schematics for this meter, given how these things are generally designed it is unlikely you'd be able to modify it in a way that does what you want without affecting other ranges. The continuity mode probably just uses the exact same configuration as the lower resistance range and then activates the beeper or lights in software according to what it reads.

author: Fungus
author_rank: Super Contributor
timestamp: February 18, 2025, 09:24:31 am
content: Quote from: danno_cj on February 17, 2025, 11:55:05 pmNo.

author: Fungus
author_rank: Super Contributor
timestamp: February 18, 2025, 09:47:20 am
content: Quote from: EEVblog on February 17, 2025, 10:47:39 pmI'm failing to come up with a scenario where it's better ... anyone?

author: EEVblog
author_rank: Unknown
timestamp: February 18, 2025, 10:19:39 am
content: Quote from: Fungus on February 18, 2025, 09:47:20 amAny application that has over that lowish 50 ohms in the line. Coils for example and long wire runs. We had these when I worked on towed array seismic cables for example.It's why the 121GW and some other meters have a programmable threshold.

author: Fungus
author_rank: Super Contributor
timestamp: February 18, 2025, 02:35:24 pm
content: Quote from: EEVblog on February 18, 2025, 10:19:39 amI always assumed jobs like that would have specialized cable testers, not a BM786.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 18, 2025, 04:04:07 pm
content: If memory servers me, if you use the diode test beep mode, it seems like the detection limits are lower. I know I tested it but did not include the data. Seems like it was still pretty high.Maybe Brymen could have used the diode check for their high detection and lowered the normal continuity test to something more in-line with other meters... I never asked them about it.

author: Fungus
author_rank: Super Contributor
timestamp: February 18, 2025, 04:38:02 pm
content: Quote from: joeqsmith on February 18, 2025, 04:04:07 pmThat would be smart.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 18, 2025, 05:14:03 pm
content: Quote from: Fungus on February 18, 2025, 04:38:02 pmI wrote them describing the problem and offering the suggestion. They can also review thresholds for other products. I'll post an update when I hear back from them.

author: bdunham7
author_rank: Super Contributor
timestamp: February 18, 2025, 07:01:53 pm
content: Quote from: joeqsmith on February 18, 2025, 04:04:07 pmFrom the manual, the diode test current is 0.35mA and the lower threshold for short detection is 100mV, so that's about 285 ohms, same as the continuity threshold. I'm guessing they use a separate circuit to activate the buzzer instead of relying on the ADC readings because they want a fast response. Maybe that's associated with the bar graph circuit or maybe not, but it seems like they may be reusing the same system for the beeping function.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 18, 2025, 08:06:10 pm
content: Quote from: bdunham7 on February 18, 2025, 07:01:53 pmI want to say it was less than 200 (80 or so lower). Actually, I have that brand new 789 that I could measure if you like. When I was originally looking at these meters, I was swapping ICs and what not. The meters always appeared to be in cal but they were concerned on that last go around. Easy enough to test. It may not be low enough for OP.***BM789, final production, Firmware 78911. Continuity full on: 278 ohms, off: 320 ohms. Diode Check full on: 206 ohms, off 207 ohms.I then check the two BM786 prototypes. One with 78605, the other with 78609. Both appear spot on with the 789 in both modes. So while a fair amount lower in diode check as I remembered, they are still pretty high when compared with other meters I have looked at.

author: EEVblog
author_rank: Unknown
timestamp: February 18, 2025, 11:00:47 pm
content: Quote from: joeqsmith on February 18, 2025, 08:06:10 pmHow do you have 786 prototypes?

author: EEVblog
author_rank: Unknown
timestamp: February 18, 2025, 11:03:22 pm
content: Quote from: Fungus on February 18, 2025, 02:35:24 pmThey do, for production. But if you are just troubleshooting then it can be handy.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 18, 2025, 11:27:45 pm
content: Quote from: EEVblog on February 18, 2025, 11:00:47 pmBrymen provided them per my request prior to the release and I hung onto them. Of course, you knew that already.The last video I made beating the crap out of it.

author: EEVblog
author_rank: Unknown
timestamp: February 19, 2025, 01:31:03 am
content: Quote from: joeqsmith on February 18, 2025, 11:27:45 pmI wouldn't call those prototypes, would be the same production units as my first batch.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 19, 2025, 01:42:00 am
content: Quote from: EEVblog on February 19, 2025, 01:31:03 amCall them what you like. By the time you had ordered the first batch for sale, we had made several changes to these. Most of which was shown on camera.

author: floobydust
author_rank: Super Contributor
timestamp: February 19, 2025, 02:18:42 am
content: Looking at how the continuity function is (commonly) implemented - the ADC is too slow to use a threshold (in firmware) for the fast beeper response.Instead, the DMM IC has a window-comparator subsection with a few programmable reference voltages (ratiometric of rail voltage), and hysteresis. But it ends up with the PTC and surge resistor as part of the voltage divider. Those parts have poor tolerances ±20% for the PTC cold and another ±5-10% for the surge resistor depending on the manufacturer. As well, add in the DMM IC CMOS-switches also have resistance around 80Ω that varies, and then there is the comparators' offset voltage.I'm saying the threshold variation is likely due to the hardware.The actual beeper threshold I would expect some flexibility but maybe not if the test current is low, comparator already on the most sensitive levels.

author: EEVblog
author_rank: Unknown
timestamp: February 19, 2025, 02:24:15 am
content: Quote from: floobydust on February 19, 2025, 02:18:42 amAlso, meters with a bargraph have a secondary faster updating ADC, and some meters use that for the continuity.In the case of the BM786 that has 100us response time, yeah, it's got to be a comparator.

author: bdunham7
author_rank: Super Contributor
timestamp: February 19, 2025, 02:52:02 am
content: Quote from: floobydust on February 19, 2025, 02:18:42 amIf the current is constant, then variation in the output leg impedance won't matter. The input leg will be very high impedance (10M or maybe more) and variation in those parts in the input leg shouldn't matter either.

author: floobydust
author_rank: Super Contributor
timestamp: February 19, 2025, 04:12:07 am
content: Yeah that's what I thought as well, leaving no reason for the big fat variance.Example configs show two different ways to measure resistance, constant current or constant voltage.For continuity, I'm a bit sleepy to dig in enough and ascertain if a silicon limitation (comparator config) is why it (looks like) constant voltage is being used, which involves the PTC's resistance. It's (overly) complicated.

author: bdunham7
author_rank: Super Contributor
timestamp: February 19, 2025, 04:28:11 am
content: Quote from: floobydust on February 19, 2025, 04:12:07 amOK, I think I get what you're saying here. There are some older DMMs that don't use a constant test current for resistance, instead they use a known internal resistance in series and do successive voltage measurements on each and then compare them. Obviously this would never work the same way on modern meters with a potentially variable resistance added in. I do know that many meters do not use a constant current for the diode check, nor do they really need to as long as the current is always reasonable and hopefully close to 1mA @ 0.7Vf. A continuity check that reads in ohms could work similarly, but instead of just comparing two resistors they would measure the voltage drop on the internal resistor to determine the actual test current and then calculate the resistance from the voltage drop present across the inputs. But that would be too slow for the continuity beeper so they simply use the raw, uncorrected voltage present at the inputs for the comparator. And that very well could be the same exact circuit as the diode test range.This would be easy enough to check if you had one of these meters--just warm up the PTC and then see if the continuity threshold shifts downwards temporarily.

author: EEVblog
author_rank: Unknown
timestamp: February 19, 2025, 05:02:04 am
content: Quote from: bdunham7 on February 19, 2025, 04:28:11 amThe BM786 does this.Shove 240V up the ohms range and then measure a resistor and it reads lower and then creeps back up as the PTC cools down. Same in both ohms range and continuity range.

author: bdunham7
author_rank: Super Contributor
timestamp: February 19, 2025, 05:35:06 am
content: Quote from: EEVblog on February 19, 2025, 05:02:04 amI just tested two meters, Fluke 27 and 289, and they do something similar but for a slightly different reason. Of course I used 1000VAC not just measly mains voltage, got them good and warm, then put 100R across them. They each took about 10-15 seconds to range down and then another 10-15 seconds of reading too low before they recovered. They didn't recover asymptotically, they quickly went straight to the correct reading and stayed there. These meters both use relatively constant (27) or exactly constant (289) test current, but if the PTC is too hot the compliance voltage isn't enough to overcome the resistance and the test current will be too low--as will the reading. Once the test current is back within compliance limits, the meter will be accurate even if the PTC changes further.On a meter that does not use a constant test current, I don't know how that whole thing would play out. I'm assuming the resistance readings are compensated somehow internally for this so that PTC variance won't affect the accuracy--otherwise your meter would read quite low if it were out in the sun. So to test my theory, get the meter warmish--like 45C or something--and then test both the resistance readings and the continuity threshold. Then put it in the fridge and cool it off and try again. If I'm right, the resistance readings will be more or less accurate hot or cold, but the continuity threshold will be signifcantly lower for the hot meter. That might even make a good video...

author: joeqsmith
author_rank: Super Contributor
timestamp: February 19, 2025, 02:56:26 pm
content: Quote from: joeqsmith on February 18, 2025, 05:14:03 pmI continue to be impressed with Brymen. They are going to investigate and get back to me.

author: Furna
author_rank: Frequent Contributor
timestamp: February 19, 2025, 04:56:43 pm
content: Quote from: joeqsmith on February 19, 2025, 02:56:26 pmI am positively impressed too; they were helping me directlyhttps://www.eevblog.com/forum/projects/brymen-bc-86p-usb-adapter-firmware-with-usbtmc-scpi/msg5404913/#msg5404913... and I am not an YouTuber/influencer ...They were helping to have an happy customer (I guess). A strategy that worked.

author: bdunham7
author_rank: Super Contributor
timestamp: February 19, 2025, 08:53:58 pm
content: For comparison purposes I tried my two meters continuity threshold at room temperature, after an hour in the fridge and then after being wamed up with a heating pad.Fluke 27: 270R normal, 255R cold and 295R warm. Note that the 27 does not read out in ohms, the continuity mode and diode mode are one and the same. The threshold is constant at about 100mV but clearly the test current is changing a bit.Fluke 289: 51R normal, 51R cold, maybe 50.5R warm, I hadn't planned on any great precision here but maybe it changed a tiny bit. Also, the 289 reads in ohms and defaults to the 500R range, but can be ranged up and the continuity beeper threshold can thus be set to ~500R, 5k, 60k, 600k and even about 1M on the top ranges.Finally, the small Fluke 116 has a threshold of 62 ohms, I didn't cool or heat it but I'd expect it will probably change some in the same manner as the 27. It uses a 9V battery like the 27.I suppose there are tradeoffs using low-power designs. The Fluke 289 is a no-compromises (on measurements) design that results in very large and expensive battery-eating monster. The Fluke 27 is on it's second 9V battery in 18 years. The Brymen is very small and running on 2 AAA cells. Perhaps the old 9V battery designs weren't so bad.I'm not sure the criticism of Brymen is warranted here. Clearly 270 ohms is not a ridiculous design choice for the continuity threshold even if some of us think that 50-ish is better.

author: EEVblog
author_rank: Unknown
timestamp: February 20, 2025, 11:44:52 am
content: Quote from: bdunham7 on February 19, 2025, 08:53:58 pmI don't have a problem with it myself.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 20, 2025, 02:01:16 pm
content: It's been a while since I have needed to trace out a large, populated board. If you're doing this on a regular basis, I could see where false reads are going to slow you down. Especially if you are using the wire brush or fast drag probing. In these cases, I wanted a very fast response and lower limits. For the occasional person checking their cables, I doubt they care.

author: Fungus
author_rank: Super Contributor
timestamp: February 20, 2025, 05:15:38 pm
content: Quote from: bdunham7 on February 19, 2025, 08:53:58 pmI checked my Fluke 27 and got the same.My Fluke 187 is around 40 Ohms.

author: Per Hansson
author_rank: Unknown
timestamp: February 20, 2025, 06:21:58 pm
content: Adding some more numbers from a few different meters:Code:Beep<Hysteresis>U1273Ax23 ΩNoUT61E30 ΩNoAN800950 ΩNoF11380 ΩNoF28-II110 Ω180 Ω

author: EEVblog
author_rank: Unknown
timestamp: February 21, 2025, 06:52:53 am
content: Brymen have responded:QuoteI'll install the new firmware and try it.EDIT: tried it and got turn on at <40ohms and turn off at 100ohms.

author: Beauvais7165
author_rank: Contributor
timestamp: February 21, 2025, 07:45:50 am
content: Quote from: EEVblog on February 21, 2025, 06:52:53 amInteresting - where to find this firmware and how to update it? I would like to test and see if this works out better.At least I don't see it on Brymens web page for download,http://www.brymen.com/Download1.html

author: EEVblog
author_rank: Unknown
timestamp: February 21, 2025, 08:06:13 am
content: Quote from: Beauvais7165 on February 21, 2025, 07:45:50 amOnly dealers who have the firmware and programmer can update it.

author: EEVblog
author_rank: Unknown
timestamp: February 21, 2025, 08:07:54 am
content: The continuity has now changed from latched to itchy and scratchy.

author: danno_cj
author_rank: Contributor
timestamp: February 21, 2025, 08:41:55 am
content: Firmware upgrade for Brymen 780 series is only available to selected people with blue blood. Ordinary people can't perform firmware upgrade, only authorized dealers can. This was a dump decision made by Brymen. So this fix add just frustration to 780 meters series users.

author: Fungus
author_rank: Super Contributor
timestamp: February 21, 2025, 09:26:21 am
content: Quote from: Beauvais7165 on February 21, 2025, 07:45:50 amThat's not the way it works.Even Dave's reply says, "You may update the firmware ofoneBM786to test."

author: Fungus
author_rank: Super Contributor
timestamp: February 21, 2025, 09:27:48 am
content: Quote from: danno_cj on February 21, 2025, 08:41:55 amMessing with firmware on a multimeter can put lives at risk.

author: Furna
author_rank: Frequent Contributor
timestamp: February 21, 2025, 10:30:57 am
content: Quote from: Fungus on February 21, 2025, 09:27:48 amThis must be the reason why the firmware upgrade is only available to dealers (which usually do not have blue blood).

author: danno_cj
author_rank: Contributor
timestamp: February 21, 2025, 12:26:58 pm
content: Blue blood meaning"A blue blood is an aristocrat. Blue bloods come from privileged, noble families that are wealthy and powerful. The word blood has long referred to family ties: people you are related to share the same blood. One specific type of family is composed of blue bloods: members of the aristocracy."Dave and and few others have the privilege to do firmware updates on Brymen 780 meters series. So is in this regard Dave and few others is one with blue blood, Brymen aristocracy. Even the blue holster from 786 proves this.

author: EEVblog
author_rank: Unknown
timestamp: February 21, 2025, 12:52:16 pm
content: Quote from: danno_cj on February 21, 2025, 12:26:58 pmI am an authorised Brymen dealer and have signed an NDA to get access to the programmer and firmware binaries.Most meters on the market do not support user firmware updating, and Brymen meters are no different in this respect.Manufacturers improve firmware in multimeters are the time as edge case bugs are discovered etc, it's just that you never see or hear about it.A fluke meter you bought last year might contain different firmware to one you buy this year. Same for any other brand.Most Brymen meters use OTP ROM based firmware, the BM780 is different in that it has a flash re-programmable instead, so it's the only model that allows firmware reprogramming by the dealer.

author: shapirus
author_rank: Super Contributor
timestamp: February 21, 2025, 12:59:56 pm
content: Quote from: EEVblog on February 21, 2025, 08:07:54 amYou used the word "slower", whereas all that we can conclude from the test you've performed, apart from the resistance threshold, is that it became non-latched, meaning, the durations of the beep and the light don't have a set minimal duration.A different test would be required to measure an actual resolution (and/or trigger sensitivity): use a microphone or hook an oscilloscope to the buzzer to see what the minimum delay between two short-circuit events (and/or the minimum duration of such an event) would be that would still result in two separate signals arriving at the buzzer (and/or would result in generating a signal).BTW, non-latched response is a huge improvement IMO -- I think latched continuity response sucks and reduces functionality, because with it you cannot (or at least it's not as convenient to) detect things like intermittent continuity with damaged cables, corroded contact surfaces etc.(or maybe latched response can be okay, but only if the latch duration is set to be very small, to where the human ear can just barely register the buzzer's sound)

author: EEVblog
author_rank: Unknown
timestamp: February 21, 2025, 01:02:52 pm
content: Quote from: shapirus on February 21, 2025, 12:59:56 pmYes, correct.But it is essentially "slower" in that the user cannot detect faster continuity events.The debate over latch vs non-latched is as old as time.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 21, 2025, 02:02:45 pm
content: I suggested they not release this version and wait to see what feedback your video garners. I also suggested if they were going to remove the latch, consider having a way to select the two modes.While your video focused on the continuity test, I suggest a quick test of the diode mode as well to make sure no changes were made.Do you have the 789 that you can check as well? It may be good to test them both just to make sure they behave the same.

author: bdunham7
author_rank: Super Contributor
timestamp: February 21, 2025, 03:25:18 pm
content: Quote from: shapirus on February 21, 2025, 12:59:56 pmAs Dave demonstrated, non-latching will miss intermittent shorts. If you had a twisted wire pair in an ethernet cable that you were testing to make sure it was open, then the new version would miss a fault that resulted in a very quick or perhaps 200R worth of conductance across the wires. There's no one fits-all solution. Short latching is probably a decent compromise, but that still won't satisfy the speed probers. For advanced continuity testing perhaps a specialized instrument with all of those parameters being adjustable would be better.

author: shapirus
author_rank: Super Contributor
timestamp: February 21, 2025, 05:25:33 pm
content: Quote from: bdunham7 on February 21, 2025, 03:25:18 pmYes it makes sense. Latching may or may not be preferrable depending on the use case. Therefore the obvious solution to satisfy everyone is to make it selectable. I'm sure it's easy to implement in firmware, but making it convenient in terms of the UI, given the limited number of controls the DMM offers, might require some thinking.

author: Furna
author_rank: Frequent Contributor
timestamp: February 21, 2025, 05:27:57 pm
content: I like the new firmware better but agree with joeqsmith the behaviour should be somehow selectable.

author: bdunham7
author_rank: Super Contributor
timestamp: February 21, 2025, 06:28:21 pm
content: Quote from: shapirus on February 21, 2025, 05:25:33 pmhttps://www.polarinstruments.com/products/toneohm/toneohm_950A.htmlThe "ideal" solution is already there (and only $3k) so the only thinking necessary is about what compromises to make to fit it all in a $100 handheld meter.IMO an interesting compromise might be to have the backlight be latched for a longer time but the buzzer either for a much shorter time or full "itchy and scratchy".

author: J-R
author_rank: Super Contributor
timestamp: February 21, 2025, 08:49:22 pm
content: Firmware updatable DMMs are common enough. I seem to recall updating my Fluke 287, Keysight U1461A and 34461A and of course the 121GW.I'm confident the BM78x firmware update procedure will be discovered at some point. It's just a matter of someone finding the motivation. Although given that Dave is a Brymen dealer and has signed the NDA, we have to suspect any such discoveries likely would be quickly cleared from the EEVblog forums.The 121GW's adjustable continuity and break detection is definitely a great feature.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 21, 2025, 09:16:29 pm
content: Quote from: J-R on February 21, 2025, 08:49:22 pmThat Keysight U1282A princess meter I ran also supports it. I think I checked when I bought the meter and Keysight had not updated the firmware for several years. Not suggesting that is a bad thing.Quick check, 1/19/2017 was the last update.https://www.keysight.com/us/en/lib/software-detail/instrument-firmware-software/u1281au1282a-firmware-update-1765967.htmlI used some crazy continuity tester for work several years back that had a headset. I think the audio frequency changed as you got closer to the short. That thing actually allowed me to track down bridges rather quickly. I want to say it was under $100. Very crude looking. Maybe someones home hobby project that turned into a product.

author: shapirus
author_rank: Super Contributor
timestamp: February 21, 2025, 10:14:20 pm
content: Quote from: joeqsmith on February 21, 2025, 09:16:29 pmThis is something that could probably be a good idea in a DMM, too. Not sure how feasible that'd be, though. Would need an appropriate speaker instead of a fixed-frequency buzzer. Not going to happen in mainstream DMMs, I think. But might be possible in some nerdier models like the 121GW.Besides, maybe not much usability unless the DMM has milliohm resolution. But somewhat inline with the very issue this topic started with.

author: Monkeh
author_rank: Super Contributor
timestamp: February 21, 2025, 10:19:06 pm
content: Quote from: J-R on February 21, 2025, 08:49:22 pmI'm not. There's not sufficient interest for it to be likely for someone to look into it.

author: bdunham7
author_rank: Super Contributor
timestamp: February 21, 2025, 10:23:58 pm
content: Quote from: joeqsmith on February 21, 2025, 09:16:29 pmIf you don't want to shell out $3k for the Polar Toneohms 950A I linked earlier, there's this:https://hackaday.io/project/3635-shorty-short-circuit-finderOr to take it to the next level, this not only finds the shorts--it fixes them!https://www.aliexpress.us/item/3256807483410438.html

author: EEVblog
author_rank: Unknown
timestamp: February 21, 2025, 11:21:44 pm
content: Quote from: J-R on February 21, 2025, 08:49:22 pmI'd say it's only a percent or two of meters on the market. Practically no low end meters have it.

author: EEVblog
author_rank: Unknown
timestamp: February 21, 2025, 11:45:37 pm
content: Quote from: joeqsmith on February 21, 2025, 02:02:45 pmI agree, and that will be my recommendation to Brymen also.QuoteI don't have a 789. And it has it's own firmware branch, so I don't have the modified binary for that.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 22, 2025, 12:58:18 am
content: Quote from: joeqsmith on February 18, 2025, 08:06:10 pmBM789, final production, Firmware 78914. Continuity full on: 67 ohms, off: 160 ohms. Diode Check full on: 206 ohms, off 207 ohms.BM786, prototype, Firmware 78612. Continuity full on: 64 ohms, off: 160 ohms. Diode Check full on: 206 ohms, off 207 ohms.So it appears to have had no effect to the diode beep on both meters. This is good. Thresholds look good. Mayne use the Range or Delta buttons to toggle between latched and unlatched modes and make it sticky like other settings.I didn't run any other tests with the firmware.

author: EEVblog
author_rank: Unknown
timestamp: February 22, 2025, 01:20:44 am
content: Quote from: joeqsmith on February 22, 2025, 12:58:18 amYou've got a programmer too?

author: tautech
author_rank: Super Contributor
timestamp: February 22, 2025, 02:32:01 am
content: Quote from: EEVblog on February 22, 2025, 01:20:44 amIt is hard to remember all that happens on the forum but IIRC Brymen sent Joe updated IC's to fit.

author: EEVblog
author_rank: Unknown
timestamp: February 22, 2025, 03:10:06 am
content: Quote from: tautech on February 22, 2025, 02:32:01 amI only just asked them to change the firmware 2 days ago, no time to ship new chips.

author: mwb1100
author_rank: Frequent Contributor
timestamp: February 22, 2025, 03:19:11 am
content: FWIW, I'm perfectly fine with the 786 here as-is

author: EEVblog
author_rank: Unknown
timestamp: February 26, 2025, 03:24:54 am
content: Brymen pointed out I was testing against the older v9, not the latest shipped v11.They changed v11 to the very fast no-latched design, so the new threshold v12 is exactly what's shipping, just that the threshold has changed. Although I think there might still be a slight difference. They did this to match the BM869S to avoid in-circuit capacitance causing false readings.They can't make it selectable due to limited firmware space.Brymen are right, for practical reasons I think the non-latched version is probably better, but I can understand those who don't agree.What this means for in-circuit testing:

author: shapirus
author_rank: Super Contributor
timestamp: February 27, 2025, 11:37:52 pm
content: Speaking of "false" continuity reading when measuring across capacitors, I wouldn't call it a bad thing. I don't imply that you meant this, of course, it's just another real user's data point.I made use of that short beep (with BM869s) on many occasions as a useful indication that there is indeed some noticeable capacitance between the points being probed, which is neither a short, nor an open circuit situation. It can be used to understand that the circuit in that particular section is behaving as expected, or the opposite.p.s. this apparently means that the continuity tester implementation in BM869s is at exactly the sweet spot for me. Itchy-scratchy beeping, easily allowing to detect intermittent contacts, and at the same time the latching time (or whatever way it's implemented) is long enough to produce an audible beep when probing capacitance (which should be high enough for that of course, not sure what actual value is).

author: EEVblog
author_rank: Unknown
timestamp: February 28, 2025, 12:29:52 am
content: Quote from: shapirus on February 27, 2025, 11:37:52 pmYes, the BM786 should match the BM869S continuity response now. That wasn't the case in early BM786 and they changed it due to user feedback.Brymen agree that selectable latched/unlatched would be best for a variety of users, but they just can't it fit in the firmware unfortunately.There are definite pros and cons to both approaches.

author: mwb1100
author_rank: Frequent Contributor
timestamp: February 28, 2025, 02:31:15 am
content: I'd agree with@shapirus. As more or less total noob I would be confused by the short beep from a capacitor "fooling" the continuity test. I fact I'm certain I have been confused in the past by a short beep. I'd write it off as a glitch or something.Much better that I understand what's going on - especially since it seems that large caps cause the problem even on meters that are immune to the blip on 0.1uF caps.