Simple Cable Tracer Circuit

A cable tracer circuit is a two part electronic device used to locate and identify specific cables within a bundle or behind walls.

It consists of two main units: a transmitter and a receiver.

Cable tracers are commonly used in various applications i.e telecom and networking, electrical troubleshooting, security and alarms and audio/video Installation etc. 

Circuit Working for Cable Tracer Transmitter Circuit:

Parts List:

In the above diagram the circuit creates a flashing LED light that is inductively coupled to a transmitter circuit.

This allows you to trace the path of a cable by following the signal with the receiver.

Below are the working process of the circuit:

 When power is applied to 6V the circuit powers on.

 When the push button is pressed current begins to flow through transistors Q1 and Q2.

The transistors BC547 are configured in a common emitter configuration.

As current flow through these transistors they amplify the signal.

Capacitor C1 controls the charge and discharge cycle which sets the flash rate of the LED.

Transistor Q3 is also a BJT configured as a common collector amplifier.

It buffers the signal from the multivibrator circuit and supplies current to the LED.

The LED lights up as it receives current from transistor Q3.

 The cable that is being traced is connected to the input point to cable as shown in diagram.

When the cable is close to the transmitter circuit the signal is picked up by the receiver at the other end and converts into an audible tone.

Formula:

An oscillator circuit that alternates constantly between its two unstable states without the need for external triggering is known as an astable multivibrator.

An astable multivibrator can be used in a cable tracer circuit to provide a continuous signal that can be fed into the cable that has to be traced.

The following is the main formula and things to think about while creating an astable multivibrator circuit:

The oscillations frequency f:

The following formula may be used to get the estimated frequency of oscillation f in an astable multivibrator:

f = 1.44​ / (R1+2 * R2) * C

where,

• The resistors that are linked to the capacitors are R1 and R2.
• C is the capacitors capacitance C2 in diagram.

Note:

An estimated frequency is given by this formula.

Use the capacitors actual charging and discharging times for calculations that are more precise.

Choosing component values for an astable multivibrator that may efficiently propagate through the cable being traced is a necessary step in designing an oscillation frequency that is desired for a cable tracer.

Depending on the demands of a particular application and the surrounding circumstances, adjustments could be required.

How to Build Cable Tracer Transmitter Circuit:

To build a Cable Tracer Transmitter Circuit follow the below mentioned steps for connection:

• Connect the collector of transistor Q1 to positive supply through a resistor R1.
• Connect the base of transistor Q1 to resistor R3.
• Connect the emitter of transistor Q1 to ground.
• Connect a capacitor C1 to input of to cable.
• Connect the collector of transistor Q2 to positive supply through resistor R4.
• Connect the base of transistor Q2 to resistor R2 and capacitor C2.
• Connect the emitter of transistor Q2 to ground.
• Connect capacitor C3 between resistor R3 and R4.
• Connect the collector of transistor Q3 between the junctions of two resistors R2 and R3.
• Connect the base of transistor Q3 from positive supply to ground in series through a resistor R5 and a flashing LED.
• Connect the emitter of transistor Q3 to positive supply.
• Connect a push button to the positive supply of 6V battery.

Circuit Working for Cable Tracer Receiver Circuit:

Parts List:

The above diagram is a cable tracer receiver circuit following are the working details:

The circuit picks up the signal from the transmitter unit via the coil.

This coil acts as an antenna.

Choke coil while the inductance value 10mH is not critical using a coil with more windings will improve performance.

 The transistors Q1, Q2 and Q3 amplify the weak signal received from the coil.

 Capacitor C4 and resistor R5 form a high pass filter that eliminates any low frequency noise from the amplified signal.

This helps isolate the specific signal from the transmitter.

 Transistors Q4 and Q5 act as an audio amplifier circuit.

They further amplify the filtered signal so it can drive the loudspeaker.

A standard miniature speaker is recommended for better sound volume compared to a smaller 16Ω earpiece.

The speaker outputs a tone, allowing you to hear and trace the cable that the transmitter is connected to.

Additional Note:

• C1, C2, C3 and C5 are bypass capacitors that help to regulate the voltage supply within the circuit.
• R1, R2, R4, R6, R7, R8 and R9 are resistors that set the various bias currents and voltage levels within the transistor circuits.
• The low standby current 50mA allows you to use a simple push-button switch to turn the circuit on and off.
• The push button switch serves as a power switch for the receiver circuit.

How to Build a Cable Tracer Receiver Circuit:

To build a Cable Tracer Receiver Circuit follow the below mentioned steps for connections:

• Connect capacitor C1 to the input signal of to cable through the base of transistor Q2.
• Connect the collector of transistor Q1 to positive supply through resistors R2 and R3.
• Connect a resistor R4 through a collector and base of transistor Q1.
• Connect the positive side of capacitor C4 to the base of transistor Q1 and negative side of C4 to ground.
• Connect the emitter of transistor Q1 to ground through a 10uH coil.
• Connect the collector of Q2 through R6 resistor .
• Connect the base of transistor Q2 through series of capacitor C3, resistor R1 and capacitor C1 to input supply of to cable.
• Connect emitter of transistor Q2 to ground.
• Connect collector of transistor Q3 to base of transistor Q5.
• Connect base of transistor Q3 to collector of transistor Q4.
• Connect emitter of transistor Q3 to positive supply.
• Connect the collector of transistor Q4 to the base of transistor Q3.
• Connect the base of transistor Q4 to the series of resistors R7 and R8 from positive to negative power supply.
• Connect the emitter of transistor Q4 to ground through resistor R9 and capacitor C6.
• Connect the collector of transistor Q5 to positive supply.
• Connect the base of transistor Q5 to collector of transistor Q3
• Connect the emitter of transistor Q5 to ground through a 16 ohm mini speaker.
• Connect a push button through a positive supply of 3V battery.

Note:

• Building electronic circuit can be risky if proper safety precautions are not followed.
• It is recommended to consult with a qualified electronics professional before attempting to build this circuit.

Conclusion:

To conclude, The transmitter inject a distinct audio signal into the target cable.

The receiver then pick up this signal through inductive coupling or by following the electromagnetic field around the cable.

By amplifying this weak signal and filtering out noise the receiver produces an audible tone allowing you to trace the path of the cable.

These circuits are relatively inexpensive and easy to build making them a valuable tool for identifying wires in bundles or behind walls.

References:

Cable locator