Simple continuity tester

Discussion in 'The Completed Projects Collection' started by Robartes, Feb 19, 2015.

  1. Robartes

    Thread Starter Member

    Oct 1, 2014
    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:


    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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    Last edited by a moderator: Feb 19, 2015
    Metalmann, absf and planeguy67 like this.
  2. #12


    Nov 30, 2010
    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.
  3. Robartes

    Thread Starter Member

    Oct 1, 2014
    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
    Metalmann and #12 like this.