Introduction: How to Make a Connectivity or Continuity Tester With Light & Buzzer Indication

In this tutorial i will show you how to make a connectivity tester using BC107. This circuit or project comes with two types of indication 1. Buzzer & 2. Light Indication.

Please watch the video for making this circuit or continue reading for more technical details & circuit diagram

Step 1: Things You Need

Picture of Things You Need

Part List :

1. BC107

2. 5V Buzzer

3. Red LED

4. Resistor (330 or 470)

5. PCB Board

6. Male Header

7. 3 Terminal Block


Purchase List or Affiliate Link

Amazon IND
1. Buzzer -

2. LED -

3. BC107 -

4. Resistor(330 & 470) -

5. Female Header -

6. 3 Terminal Block -

Amazon USA

1. Buzzer -

2. LED -

3. BC107 -

4. Resistor(330 & 470) -

5. Female Header -

6. 3 Terminal Block -

Ali Express

1. Buzzer -

2. LED -

3. BC107 -

4. Resistor(330 & 470) -

5. Female Header -

6. 3 Terminal Block -

Step 2: Circuit Diagram & Finished Project

Picture of Circuit Diagram & Finished Project

Complete the circuit as shown in the circuit diagram.

Technical Details :

This circuit can work with 1.5 volt to 9 volt input.

Note 1: when connected to a 1.5 Volt source only the buzzer will work. The reason for LED not to work is the forward voltage of an Red Led will be 1.8 Volts which is greater then our input voltage. For both the indication to work you need to at least 2.5 to 3 volt input.

Optional : If you don't both the indication then you can remove any one. For example if you need only the Buzzer indication replace the LED with buzzer. (+ve of the Buzzer to the one terminal of 330 ohm resistor & -ve goes to the common of BC107)

Note 2 : If you don't have BC107 you can replace with 2N3904 or BC550

Final Image Details : The circuit to perform you need 4 inputs

1. Probe A

2. Probe B

3. Vin

4. GND

In the finished images you can see i marked the terminal as 1, 2, 3

1 is for Probe A, 2 is for Probe B & Vin & 3 is for GND. Note - (This depends on how you make your circuit). For making the circuit as i did please watch the video which is posted along with tutorial in the first page.


BeachsideHank (author)2017-06-10

My continuity tester is made from the voice module taken from a discarded plushy Santa figure. I also installed an LED, but the audio portion is great, when troubleshooting I don't have to look away towards the light, just listen for the jingle "We Are Santa's Elves", nice thing about it is that the circuit latches "on", so one needs to give a confirming tap again to turn it off. Cost of course, was $0.00 U.S.D.☺

Nice Work :)

MakeStuff_MS (author)2017-06-10

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About This Instructable




Bio: I like making new things from trash. For more cool content please subscribe to my YouTube channel @
More by MakeStuff_MS:+12/-12 Volt Transformer Based Dual  Voltage Power SupplyMusic Reactive or Sound Activated LED Strip LightsIC Based Simple 12V to 240V Inverter Using MOSFET & IC 4047
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