# How to make a continuity tester with light and sound

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Solve the faults in a simple way with this continuity tester with sound and light that you can do in a homemade way and with simple materials.

# How to make a continuity tester with light and sound

Today I bring you at the request of a subscriber a fairly simple circuit to do with recycled materials and is quite useful as a search tool for those failures that are hidden behind a false contact, cut wire or fuse damaged. That's right, today I'm going to explain how to build a sound continuity tester.

We need to build it:

-  01 NPN 2N2222 Transistor (Q1)
-  01 Transistor PNP 3906 (Q2)
-  01 Normal Red LED.
-  01 390 Ohms Resistor (R2)
-  01 47k ohms Resistor (R1)
-  02 1.5 V Batteries
-  01 Piezoelectric (LS1)
-  01 inducer or coil whose resistance is between [5 and 15] Ohms
-  01 Capacitor 33nF (C1)
-  01 Capacitor 100uF

Note: For the inductor or coil, take it out of a burnt saver bulb. It is the high frequency ballast works perfect on this device.

## Mounting circuit

As you can see in the image above, the circuit has few elements, but has enough connections. Lol. This is why you have to be very careful when assembling do not be mistaken. Above all, in the bases of the transistors (the central leg of the transistor) because a bad connection at this point irreparably damages it.

Anyway for the most experienced I leave this other circuit with electronic symbology to see better ; )

## How the Circuit works

Some of the issues I wanted to meet for this circuit were:

Make it as simple as possible "without using spider" (integrated circuits).

-  That the current consumption was minimal.
-  That out of sharp sound.
-  Could somehow know whether or not there is continuity and its magnitude.
- Low operating voltage to be safe in TTL circuits.

This is a modified metronome whose association of Q1, Q2, R1 and C1 generate a very short-lasting pulse, where the frequency depends on the values of R1 and C1. Of course, to generate this pulse, it is necessary to connect a load to the output that is between 4 and 20 ohms preferably, in this case a small horn would look good. The problem is that they consume a lot of energy, so I decided to use a piezoelectric. To do this I added a small high impedance coil in parallel to achieve the oscillation that this element needs. And so left the circuit of the previous image that can be used with batteries of the type button to 3v obtaining a sound quite... say that audible (not to say annoying lol).

Its operation is simple, when placing a cable between the test terminals closes the circuit and initiates the process of oscillation at high frequency audible by the piezoelectric. The LED will light if low resistance is available between the terminals under test (between 0 and 150 ohms). Otherwise you will only hear a slight sound indicated by this to the operator that there is continuity of the circuit, but the impedance is high to circulate electric current.

## How to use it?

When using the appliance, familiarise yourself with the sound at resistance 0 (join the two ends). In this way you can evaluate the amount of resistance that exists under test based on the sound.

Another important thing is to always check that there is no tension between the elements to be tested as the circuit will burn. As with other mid-level commercial testers. I did not include a surge protector in the design; ).

Connect the test leads to the element to be tested, pay attention to the sound and the ignition of the LED. The following table indicates the operation summary.

 Sound Led On Description of the problem Yes Yes Low or zero resistance, if both the sound and the lighting of the LED is strong. Yes No High resistance, between 150 and 1000 ohms. There is likely to be false contact or measuring an electrical circuit. No No No continuity

## Design Considerations

Make sure that the battery does not exceed 3, 5v or the LED will burn (note that it has no resistance).

If you do not have the piezo, remove the L1 coil and place C1 = 1uF and R1 = 10k ohms and a serial resistor to the LED of at least 690 ohms. Finally increase the operating voltage to 9v.

If you do not like the tone being generated and want to edit it, place R1 = 5000 ohms and add a 250 K ohms potentiometer in series. By changing its value, you can get different shades.

Well, that's all for today, I hope you like it and can implement it.

I leave a video of how I did it:

## Do you have questions or doubts?

Questions or suggestions can use the form below and I will gladly answer them.

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written by

Chica Mecánica

19/04/2018

04/19/2018

Chevere

Facíl como siempre Dennis.

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How to make a continuity tester with light and sound

Solve the faults in a simple way with this continuity tester with sound and light that you can do in a homemade way and with simple materials.

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