The Continuity Tester!




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Hey Guys, I am back to instructables after a really long time. I'd been busy for a long while now, so let's get back to topic.The Name itself describes this project. ''The Continuity Tester !!''

Anyways, Recently I destroyed my Digital Multimeter while working with an AC project, so I needed an alternative to test my prototype circuits, so I thought this should do the job. Well, Enough of this intro, let's Build it!!

Step 1: Gather the Components!

For this project, the components I used, most of them I salvaged from older circuits. (Don't Worry I'll upload that one day)

OK, moving on, You'll need:

1) Piece of Perf Board or ProtoBoard( I had a piece laying around)

2)A 6-12V Piezo Buzzer (I think that's what its called or simply put 'A Buzzer')

3)2 Leds (I used one Green and another Red led)

4)2X100 ohm Resistors (I could have used 1k ohm resistors but it reduced the sound intensity of the Buzzer)

5)9V Battery and Battery Clip


You'll also need Soldering Iron and Wires but yeah those are the necessary things so no need to specify.


Step 2: Testing the Circuit !

The most important part of any build is to test your circuits. Use a breadboard, Test the circuit and then you're off to prototyping!

I have added the circuit diagram in the picture above.

Apparently due to technical issues, I couldn't upload the video of the prototype of my continuity tester so please bear with me in this instructable.

Optional Update :
You could add a 5V regulator to the above circuit if you'd want to make the LEDs survive for longer period.(I didn't do that as my battery had dropped its voltage to roughly about 5V)

Step 3: Make It Permanent!

Solder the components according to the circuit diagram and then you're done!

(I actually forgot to add probes to this circuit so that I could connect them to any circuit and test it.)

This circuit was a great build and it works like a charm.

Consider supporting me on patreon and follow me YouTube, if you want some more updates on my projects!

Thanks For Reading!

Post Plans:

I have plans of embedding this circuit in the next project, So stay tuned for that!!!

That's all for today FOLKS! Have a nice day!



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    15 Discussions


    1 year ago

    NOTE: Thanks to all of them who corrected me in this instructable. I have updated the schematic.


    1 year ago

    The only error is that the schematic is wrong, I did this circuit even before the schematic and the circuit works just fine. I will correct the schematic as soon as possible.


    1 year ago

    Nice and simple.
    Although I would be cautious when using this with more sensitive electronics since the 9V might be a little high for some components. Having the buzzer, R1 and the LED limit the current nicely so it might not become a real issue. But looks handy for testing simple circuits. And by the way shouldn't the red LED be the other way around in the schematic?
    Anyways good luck with future projects:)

    4 replies

    Reply 1 year ago

    I think there might be an error in the schematic, yeah thanks for informing.


    Reply 1 year ago


    There seems to be more than one error in the schematic and since it isn't possible to get the wiring from your other pictures, it's quite necessary that it represents the circuit as you claim to work.

    I assume that J1 is where your probes go (?)

    Besides the reversed LED2, it seems (not sure though) that the buzzer is in parallel with the serially connected R1 and LED2.

    Even if you fix this, I can't see it working:

    With a fresh battery (9V) you push (9V-~2V)/100 = 70mA (way too much for a regular LED) and with a flat battery (5.4V) it still too much: (5.4V-~2V)/100 = 34mA.

    Further, the circuitry at the right of LED1 is voltage limited to around 2V, as LED1 is acting as a shunt regulator, same as if you had a 2V zener diode in its place - so even if you fix the orientation of LED2 and have the buzzer "on its own", LED 2 will only get a current of around 0.2V/1k = 200µA or 0.2mA ! Barely visible and LED1 won't change, but is still committing suicide, washing out the faint glow of LED2 (if any).

    The buzzer if connected as I think it is (on the SLBB), will be mute or at least very low on ~2V.

    My best advice... Back to square one and rethink the circuit from the ground up - as is it's probably harder to fix, than make a fresh start.

    If I can be of any help, please let me know (e.g. in a P.M.)

    Have a nice day :)


    Reply 1 year ago

    You are right, having the LED1 and R2 this way acts as a regulator, so no higher voltages to the probe (Should have seen that:P). Although it seems that other problems arise. Wouldn't it be most convenient to use Transistor or comparator/Op-Amp(as a comparator) to separate the LED and the buzzer from the probes to lower the probing voltage and current to minimize the risk of frying your circuit? Of course this makes the circuit more complicated and kills the original idea.


    Reply 1 year ago

    Let me upload the video of this build soon, then u can see it for urself. Cool?


    1 year ago

    hint led 2 is shown reversed also r 2 at 100 ohms 9 volts do the math led 1 current = ??? 90 ma . not sure resistance of your buzzer or current needs but r 1 seems a bit large without the buzzer led would draw 9 ma

    1 reply

    Reply 1 year ago

    The circuit works just fine but my battery had a dropped voltage of 4.8 volts when i tried with this circuit.