Continuity Tester

[luudee]

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

[mendip_discovery]

I am assuming you mean Continuity Tester

Martindale,

• TEK402
• Probe voltage: 9V DC approx
• Test current: 5mA
• Continuity range (audible): up to 10k: nominal
• Audible output level: 85dB minimum at 30cm with leads shorted
• Overvoltage protection fuse rating: 50mA, 250V, Fast Acting Ceramic Fuse,
• TEK404
• Probe 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 shorted
• LED indication: bright orange LED Buzzer and LED intensity reduce with increasing continuity resistance

[luudee]

I am assuming you mean Continuity Tester

Martindale,

• TEK402
• Probe voltage: 9V DC approx
• Test current: 5mA
• Continuity range (audible): up to 10k: nominal
• Audible output level: 85dB minimum at 30cm with leads shorted
• Overvoltage protection fuse rating: 50mA, 250V, Fast Acting Ceramic Fuse,
• TEK404
• Probe 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 shorted
• LED indication: bright orange LED Buzzer and LED intensity reduce with increasing continuity resistance

Yes, 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

[Gyro]

Build your own for little cost? ...

[Fungus]

TEK402

• Continuity range: 0: to 2.2k: ± 10%

That's a long way from 1 Ohm...

Any pointers, suggestion?

Get one with a light?

[newbrain]

Maybe this DIY from Leo?
< 5 Ω, and very robust.

[mendip_discovery]

TEK402

• Continuity range: 0: to 2.2k: ± 10%

That's a long way from 1 Ohm...

It is still in range. I guess you could always add a 2.199k resistor/trim pot to the circuit if you like.

[kripton2035]

build your own ...
http://kripton2035.free.fr/Projects/shorty-display.html

[tooki]

Maybe this DIY from Leo?
< 5 Ω, and very robust.

FYI, 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.

[Fungus]

One of my best continuity testers is the $8 Aneng AN9205A. The beeper is loud, the LED is VERY bright (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.html

I don't know if it would survive being connected to mains or not. 

[Gyro]

As far as I can find, the AN9250A has a continuity threshold of 30R +/- 10R. Lower than many but still well a 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.

[Fungus]

As far as I can find, the AN9250A has a continuity threshold of 30R +/- 10R. Lower than many but still well a bit short of the 1R threshold that the OP is requesting.

I 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.

[Gyro]

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.

[KungFuJosh]

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.

What's the point of the 1MΩ range? Is that for checking bad insulation or something?

[Gyro]

Exactly that, contamination on PCBs etc.

[hugo]

I did a google search and didn't see anything ...

You'll find a simple, inexpensive and well enginnered diy continuity tester, called "In-Circuit Conduction Tester" at http://elm-chan.org/works/cch/report_e.html

Vtest: 500mV
Itest: 100μA

[rhb]

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

[bdunham7]

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.

Bench 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.

[Fungus]

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. 

[J-R]

FYI, the 34401A continuity threshold can be set from 1-1000 Ohms.  Default is 10 Ohms.

[KungFuJosh]

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.

[rhb]

FYI, the 34401A continuity threshold can be set from 1-1000 Ohms.  Default is 10 Ohms.

True. 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

[Fungus]

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. 

"Current limiting" means the voltage will drop instantly when there's low resistance.

It's how current limiting works (Ohm's law).

[JohnC]

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.html

There 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 storage 

In 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.

[BeBuLamar]

I don't know of one that only indicates continuity for less than 1 ohm.