Cheap Continuity tester?

Discussion in 'General Electronics Chat' started by musicalavtech, Mar 19, 2016.

  1. musicalavtech

    Thread Starter Member

    Mar 23, 2012
    32
    3
    What values of resister and led would work in series with a cheap tone generator, and a 9V? Only needed to check unpowered wiring circuits for shorts.
     
  2. ISB123

    Well-Known Member

    May 21, 2014
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    Sinus23 and #12 like this.
  3. #12

    Expert

    Nov 30, 2010
    16,261
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    9 volts, 1K, and an LED...in series.
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    Do you need the tone generator? Couldn't the LED serve as your indicator?

    Are you testing points that could be damaged by 9V?
     
  5. dl324

    Distinguished Member

    Mar 30, 2015
    3,242
    619
    Many DVM's have an audible continuity checker.

    The continuity checker I use most uses 2 AA batteries and a flashlight bulb. An added benefit is that it can check diode junctions and most LEDs. The last time I bought one they were a couple dollars.
     
  6. musicalavtech

    Thread Starter Member

    Mar 23, 2012
    32
    3
    It's just for point-to-point wiring on a panel that is unpowered. To quickly check for shorts before powering up. I have a meter to use after powering up, to check voltages. I know 2 leads, battery, and buzzer is the super simplest, but I thought to add a led for noisier environments. I don't even need a switch.

    #12 mentioned a 1k resistor, as long as a buzzer or other cheap audible would work.

    Because the panels are good size, with no good place to set a meter, is why I want to use this.
     
    Last edited: Mar 19, 2016
  7. #12

    Expert

    Nov 30, 2010
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    Adding an LED in parallel with the buzzer will not stop the buzzer.
     
  8. RichardO

    Well-Known Member

    May 4, 2013
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    I have 2 continuity testers.

    The simple one is an old Sonalert with a 9-volt battery. Shorting the leads powers it up. This is fine for cables that are not connected to anything. It also is a quick way to test LED's. I never use it in a circuit because of its high voltage and current.

    The other continuity tester is more specialized. Since its open circuit voltage is less than a diode drop, it can safely be used in IC and transistor circuits. It only beeps if the resistance is less than about 100 ohms. This beeper is used to verify correct wiring of prototype circuits or to follow traces on a PCB.
     
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