Products > Test Equipment
Continuity Tester
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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:

--- Quote from: J-R on July 25, 2023, 06:42:34 am ---FYI, the 34401A continuity threshold can be set from 1-1000 Ohms.  Default is 10 Ohms.

--- End quote ---

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:

--- Quote from: rhb on July 26, 2023, 01:47:49 am ---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. 

--- End quote ---

"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  :D

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.
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