Simple continuity tester

Thread Starter

Robartes

Joined Oct 1, 2014
57
This one came about as I was soldering some other circuit together. As I am a bit ham-handed with a soldering iron, I tend to make solder bridges where there shouldn't be any, so while working I am constantly checking continuity (or lack thereof) between neighbouring contacts. I got a bit tired of having to break out a multimeter, plug in the leads, set it to continuity and then fight with the long leads and probes hanging in my way.

....................................................


So I decided to build something quick and dirty. Design parameters (such as there are for such a small project) were:

- battery powered
- always on - no on/off switches or anything
- light weight
- smallish

This is what I came up with - a dead simple 555 based oscillator driving a small piezo buzzer:

continuity_tester_schematic.png

The low side switching transistor is biased so that a resistance between the probes of lower than 150 ohm or so turns it on, sounding the buzzer.

Cobbled together it looks like this:

continuity_tester_1.jpg continuity_tester_2.jpg continuity_tester_3.jpg

Simple, maybe too simple, but it has served me well several times already.
 

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#12

Joined Nov 30, 2010
18,224
We need a parts list. I went looking for a buzzer that doesn't need a 555 chip and found nothing around 1 inch in diameter with a reasonable price.
 

Thread Starter

Robartes

Joined Oct 1, 2014
57
We need a parts list. I went looking for a buzzer that doesn't need a 555 chip and found nothing around 1 inch in diameter with a reasonable price.
Here's the parts list, as far as it goes:

- the buzzer is a LD-BZEN-1201, it came with one of those ubiquitous Arduino starter kits off Ebay. The buzzer's resonant frequency is 2.4kHz IIRC.
- the 555 is a TLC555 (standard ones don't run off 3V)
- the transistor is a 2N2222
 
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