Continuity Tester - Page 1
Forum section: electronics / testgear

author: luudee
author_rank: Frequent Contributor
timestamp: July 24, 2023, 12:36:04 pm
content: Hi Guys,I am looking for a simple, standalone continuity tester.Must have a loud buzzer, lol.It should report a close connection when the total resistance is below 1 ohm, would be great if that can be adjusted.It should also use very small currents for the test, don't want to break any potentially still connected components.I did a google search and didn't see anything ...Yes, I have several multi meters that can do that, but they are typically occupied doing some more serious work,and most of the I can't hear the efing buzzer ...Any pointers, suggestion?Many Thanks,luudee

author: mendip_discovery
author_rank: Super Contributor
timestamp: July 24, 2023, 01:11:48 pm
content: I am assuming you mean Continuity TesterMartindale,TEK402Probe voltage: 9V DC approxTest current: 5mAContinuity range (audible): up to 10k: nominalAudible output level: 85dB minimum at 30cm with leads shortedOvervoltage protection fuse rating: 50mA, 250V, Fast Acting Ceramic Fuse,TEK404Probe voltage: 9V DC approx.Test current: <50μA (across short circuit)Continuity range: 0: to 2.2k: ± 10%Audible output level: 85dB minimum at 30cm with leads shortedLED indication: bright orange LED Buzzer and LED intensity reduce with increasing continuity resistance

author: luudee
author_rank: Frequent Contributor
timestamp: July 24, 2023, 01:28:49 pm
content: Quote from: mendip_discovery on July 24, 2023, 01:11:48 pmYes, indeed ! I did mean "Continuity Tester", thank you for pointing that out ! (I fixed that now in my post)And thank you for those suggestions !luudee

author: Gyro
author_rank: Super Contributor
timestamp: July 24, 2023, 01:30:48 pm
content: Build your own for little cost? ...

author: Fungus
author_rank: Super Contributor
timestamp: July 24, 2023, 01:35:36 pm
content: Quote from: mendip_discovery on July 24, 2023, 01:11:48 pmThat's a long way from 1 Ohm...Quote from: luudee on July 24, 2023, 12:36:04 pmGet one with a light?

author: newbrain
author_rank: Super Contributor
timestamp: July 24, 2023, 01:40:56 pm
content: Maybe this DIY from Leo?< 5 Ω, and very robust.

author: mendip_discovery
author_rank: Super Contributor
timestamp: July 24, 2023, 02:25:11 pm
content: Quote from: Fungus on July 24, 2023, 01:35:36 pmIt is still in range. I guess you could always add a 2.199k resistor/trim pot to the circuit if you like.

author: kripton2035
author_rank: Super Contributor
timestamp: July 24, 2023, 03:57:18 pm
content: build your own ...http://kripton2035.free.fr/Projects/shorty-display.html

author: tooki
author_rank: Super Contributor
timestamp: July 24, 2023, 05:35:46 pm
content: Quote from: newbrain on July 24, 2023, 01:40:56 pmFYI, I have built this on a PCB, and it works well, but I prefer a smaller value capacitor to make it respond more quickly. And yes, it survives being connected to mains!(If anyone wants it, I made a few PCB layouts for it, some THT, some SMD. (Other than the transient protection device, which only comes in SMD.))I’ve been meaning to make a latching version of it, probably using a retriggerable monostable multivibrator, so that it can react super fast but not be scratchy.

author: Fungus
author_rank: Super Contributor
timestamp: July 24, 2023, 05:59:14 pm
content: One of my best continuity testers is the $8 Aneng AN9205A. The beeper is loud, the LED isVERYbright (much brighter than it looks on video) and it's as fast as anything else I own:https://www.aliexpress.com/w/wholesale-aneng-an9205a.htmlI don't know if it would survive being connected to mains or not.

author: Gyro
author_rank: Super Contributor
timestamp: July 24, 2023, 06:21:26 pm
content: As far as I can find, the AN9250A has a continuity threshold of 30R +/- 10R. Lower than many but stillwella bit short of the 1R threshold that the OP is requesting.I think it It comes down to low cost easy home construction or paying out more to build something with a display like the Shorty (not sure off-hand if this is available as a kit / ready built).Mine is a variation on the theme of the EPE article wheatstone bridge design which achieves fast audible indication, 1R / 1M threshold and decent input protection (that can be uprated as required). Unlike the Leo design, it doesn't turn on semiconductor junctions (<300mV open circuit), I find this desirable but others may differ.

author: Fungus
author_rank: Super Contributor
timestamp: July 24, 2023, 08:22:00 pm
content: Quote from: Gyro on July 24, 2023, 06:21:26 pmI measured mine at 49 Ohms.I don't know anything that will go as low as 1 Ohm. 1 Ohm is the leads and contacts.

author: Gyro
author_rank: Super Contributor
timestamp: July 24, 2023, 08:32:52 pm
content: Yes, you do need to tweak the threshold slightly to accomodate lead resistance etc. It is doable though - my tester will trigger probing a 1R resistor but not a 1R2. Not bad for 2 wire.

author: KungFuJosh
author_rank: Super Contributor
timestamp: July 24, 2023, 08:38:14 pm
content: Quote from: Gyro on July 24, 2023, 08:32:52 pmWhat's the point of the 1MΩ range? Is that for checking bad insulation or something?

author: Gyro
author_rank: Super Contributor
timestamp: July 24, 2023, 08:43:19 pm
content: Exactly that, contamination on PCBs etc.

author: hugo
author_rank: Regular Contributor
timestamp: July 25, 2023, 12:25:23 am
content: QuoteYou'll find a simple, inexpensive and well enginnered diy continuity tester, called "In-Circuit Conduction Tester" athttp://elm-chan.org/works/cch/report_e.htmlVtest: 500mVItest: 100μA

author: rhb
author_rank: Super Contributor
timestamp: July 25, 2023, 02:04:01 am
content: I suggest you consider the likely outcome of using a 7 V (33401A) or 9 V continuity tester on a 3.3 V MCU board. And if you forward bias a transistor junction ( .3 or .7 V) you'll run the risk of spurious results.Consider using a 0.5 V 1 kHz pulse train and an op amp to boost it to 5 V with a missing pulse detector triggering a 555 configured as a multivibrator. 0.2 V in the unlikely case you're working with germanium semis.There are many ways to implement one. I made a crude 1.5 V tester using a small, not loud enough, piezo sounder. It works OK, but I concluded it really needs to be below the forward conduction threshold for silicon junctions.The Cadillac is a milliohm RC oscillator which changes tone as the resistance varies. Those will let you locate shorts as well as opens. There are lots of versions of those.Have Fun!Reg

author: bdunham7
author_rank: Super Contributor
timestamp: July 25, 2023, 03:18:51 am
content: Quote from: rhb on July 25, 2023, 02:04:01 amBench meters like the 34401A often have selectable continuity ranges and thresholds. You just set the threshold for a low value and then put a resistor just above that value across the test leads with one of those dual-banana adapters. So if your test current is 1mA just set the threshold for 10R, put a 20R resistor across it and your 'open circuit' voltage will be 20mV.

author: Fungus
author_rank: Super Contributor
timestamp: July 25, 2023, 04:25:50 am
content: I always wanted one that has an LED in the probe. If you're going the DIY route you could try doing that.Edit: You could also pull the PCB out of one of those Anengs and build it around that - just bring the LED out to the probe.

author: J-R
author_rank: Super Contributor
timestamp: July 25, 2023, 06:42:34 am
content: FYI, the 34401A continuity threshold can be set from 1-1000 Ohms. Default is 10 Ohms.

author: KungFuJosh
author_rank: Super Contributor
timestamp: July 25, 2023, 01:09:54 pm
content: The continuity threshold for the SDM3055X-E is 1 to 2000 ohms (he already has the SDM3065, which might have a broader range?), but I think Luudee wants a dedicated continuity tester, otherwise a new meter will get used for other things.However, the leads need to be taken into consideration too. I have nice test leads, but they're something like 0.8Ω by themselves according to the DMM, which means the continuity response is slow unless you set to to 2Ω, which realistically is probably fine since that's compensating for the leads, leaving ~1Ω testing.

author: rhb
author_rank: Super Contributor
timestamp: July 26, 2023, 01:47:49 am
content: Quote from: J-R on July 25, 2023, 06:42:34 amTrue. But 1 or 10 ohms, it's *still* 7.7 V at the probe tips. And ~1 mA whether the threshold is 10 or 110 ohms.The idea that limiting the current will protect a transistor junction with a 3.3 V max voltage from 7.7 V needs a bit of explanation. Put 7.7 V on an MCU 3.3 Vcc pin, brush the other probe to an unrecognized ground. I wouldn't want to bet on that part surviving.Reg

author: Fungus
author_rank: Super Contributor
timestamp: July 26, 2023, 08:03:31 am
content: Quote from: rhb on July 26, 2023, 01:47:49 am"Current limiting" means the voltage will drop instantly when there's low resistance.It's how current limiting works (Ohm's law).

author: JohnC
author_rank: Contributor
timestamp: September 06, 2023, 04:20:51 pm
content: Best circuit BY FAR that I have found is this simple design by old-timer "Tony Van Roon" who has passed away...https://www.learningelectronics.net/VA3AVR/circ/latching.htmlThere are a few mirrors of his old website online, this is the latest I can find (PCB v1.08 dated 2008)It uses a single quad-gate Schmitt Trigger IC. It can be switched to alarm upon open circuit or a short circuit. Theoretically it will only trigger at zero or infinite ohms.It has latching, and can detect a fault at 1mS but will sound the alarm until a manual button-press or an adjustable timer.Runs off 9v battery, has passive Piezo buzzer (driven by 4th gate of 4093) and LED indicator. If not loud enough you can add a FET or something to drive an active buzzer.Alas, I have had this project in the "To-Do" pile for about 5 years... however it's probably got only a few weeks more to wait. I hope the parts haven't decayed in storageIn the meantime, my go-to has been my cheopo BSIDE ADM08D multimeter which has the fastest detection of any of my meters, plus it lights up too. However it triggers under about 10 ohms.

author: BeBuLamar
author_rank: Super Contributor
timestamp: September 06, 2023, 07:36:19 pm
content: I don't know of one that only indicates continuity for less than 1 ohm.

author: Gyro
author_rank: Super Contributor
timestamp: September 06, 2023, 09:02:57 pm
content: Quote from: BeBuLamar on September 06, 2023, 07:36:19 pmSee Replies #3, #10 and #12.

author: BeBuLamar
author_rank: Super Contributor
timestamp: September 06, 2023, 10:15:33 pm
content: Quote from: Gyro on September 06, 2023, 09:02:57 pmWell DIY or modified units don't count.

author: Gyro
author_rank: Super Contributor
timestamp: September 07, 2023, 11:29:06 am
content: Quote from: BeBuLamar on September 06, 2023, 10:15:33 pmI don't think the OP specifically ruled out DIY options, he was simply asking for pointers. Maybe there isn't an off-the-shelf one. Sadly this sort of TE is changing from 'sense of achievement' to 'instant gratification'.P.S. I think the Polar toneohm products go that low, or lower, but good luck with the purchase price.