Tips On How to Make Continuity Tester With 9v Battery


When we work with circuits and electrical devices, it is advisable to have a tool that allows us to verify if said device or circuit is working correctly, or energy is reaching it. This tool is called an electrical continuity tester, and emits an alarm to show the user that the circuit is working properly. Next, we will see how to make simple continuity tester with 9v battery and in a simple way.

What is continuity?

Continuity is the occurrence of a whole track for current flow. For example, an operated closed switch has continuity. A continuity test is a fast check whether or not a circuit is open or closed. Only a closed and complete (connected) circuit has continuity.

Throughout a continuity test, a multimeter sends a small electric current through the circuit to measure the resistance in the circuit.

A meter with a continuity beeper stops ringing briefly when it detects a closed circuit. The level of resistance needed to trigger the alarm varies from meter to meter, but most indicate continuity with a measurement between 0-50 ohms.

The audio signal speeds up the measurement process, as technicians don’t have to look at the meter during the test.

Continuity tests determine:

  • If a fuse is in good condition or blown.
  • If the conductors are open or short-circuited.
  • Whether the switches are working properly.
  • If the routes of the circuit are clear (it is achieved by tracing the circuit or conductor).
  • Continuity testing should be performed only when there is NO voltage in the circuit under test.


Always unplug the appliance or disconnect the main switch before attempting a continuity test. Make sure all capacitors are safely discharged.

If contact with the voltage is made during the continuity test, most meters offer protection for overload in ohms up to the nominal voltage of the meter. For most Fluke instruments, it is 1000 V AC.

How to make simple continuity tester with 9v battery

Before trying to make a simple continuity tester, you should prepare some materials:

  • A 9 V battery.
  • A resistance of 1 KΩ.
  • An LED.
  • Conductor cable.
  • Crocodile type connectors.
  • A piece of wood or plastic.

Continuity tester

We begin the assembly of our electrical continuity tester, fixing the battery on the piece of wood or plastic, with the help of a silicone or glue gun.

Once the battery has been fixed, it is time to connect between one of the ends or poles of the battery with a tin soldering iron, using cable to the resistor. Then, the free side of the resistance we connect to one of the poles of the Led, and we connect the other pole of the Led to one of the crocodile type connectors (red connector).

It’s time to complete our device. To do this, we make a connection from the free pole of the battery to the black crocodile type connector. In this way, we will have finished the device assembly, it only remains to test it. To do this, we must place the connectors at different points of the circuit to be tested and we can visualize their operation.

How it works

The internal circuit of the device is closed when we connect two points of a circuit to the crocodiles. When doing this, the LED light turns on, indicating that indeed, electrical continuity is presented in the device to be tested.

Sound continuity tester with 741

This sound continuity tester with 741, has been designed as an instrument that has the quality of doing the tests with active components connected to the circuit.

This is a very important fact because continuity testers are commonly used with the power source that feeds the circuit deactivated.

The test tips have an open circuit output locked (fixed) to a value of 0.3 volts, and the short circuit output has been set to a current of only 1 mA.

To achieve our goal, the bipolar transistor Q1 forms a constant current source of 1 mA in its collector, and the test tip is fixed to a voltage of 0.3 V with the help of a germanium diode (D2). Germanium diodes have a voltage drop of 0.3 V, when polarized live.

The IC1 operational amplifier is configured as a Schmitt trigger, with an adjustable trigger voltage level by means of the R9 potentiometer.

This trigger point determines the maximum resistance with which the circuit will operate, and can be pre-set within the range of 0 to 90 ohms. The use of the R9 potentiometer in conjunction with the R10 potentiometer facilitates the tuning of the circuit for low-value resistor values.

Important note: when we talk about resistance, we are not talking about the physical element, but about the resistance value that the acceptable measurement that is interpreted as a continuity measurement can have.

List of sound continuity tester components

  • 1 operational amplifier 741 (IC1)
  • 1 PNP BC213L transistor or similar (Q1)
  • 1 x 5.6 V zener diode, 1 watt (D3)
  • 1 silicon diode 1N914 (D1)
  • 1 germanium diode OA47 or similar (D2)
  • 2 x 1K resistors (R4, R8)
  • 1 1.1M resistor (R7)
  • 1 resistor 2.7K (R5)
  • 1 resistor 12K (R6)
  • 1 2.2K resistor (R3)
  • 1 10M resistor (R2)
  • 1 resistor of 47 ohms (R1)
  • 1 x 20k potentiometer (R9)
  • 1 x 10K potentiometer (R10)
  • 1 x 100 nF capacitor (nanofarads) (C1)
  • 1 piezoelectric speaker U5-35R (or similar). (SP)


Current testers control continuity in cables, fuses, circuit breakers and other electrical systems. They detect if the circuit is open and if there is something blocking the path of electricity. Current testers usually consist of a battery in a housing with a test probe at one end and a test cable and contact clamp at the other. 

Once the electrical system is disconnected, the contact clamp is fastened from a cable or connection. When the test probe touches a separate wire or connection in the system, the current tester battery sends electricity through the tester and the system to complete an electrical circuit. The current tester lights up or buzzes to indicate that the circuit is closed. If the circuit is open and electricity cannot return to the tester, no indicator is turned on.

You can make this tool at home by using simple schematic. However, if you don’t have any knowledge about electronic components, it would be better to buy the finished product.

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