Simple Signal Injector Circuit

A signal injector is a helper tool for electronics.

It puts a special signal into a circuit.

This helps find problems or follow where the signal goes.

These are often used for sound and radio circuits, but they can also be used for other types of circuits too.

Circuit Working:

Parts List:

A signal injector is an invaluable tool for swiftly troubleshooting and tracing signals within a circuit.

By applying the injector to the speaker output for instance, you can promptly identify the faulty stage of a radio receiver.

If you hear the signal at the output you can then progress to the preceding stage of the circuit, such as an audio amplifier.

Continuously moving the signal injector up the stages of the circuit listening for the injected signal at each point, can help pinpoint where the issue is.

Formula and Calculations:

The above circuit consists of two cross coupled NPN transistors and two RC timing networks.

The circuit oscillates between two states, with one transistor conducting while the other is off.

A BJT astable multivibrators oscillation frequency (f) may be found using the formula below:

f = 1 / (1.4 * R * C)

where,

• f is the frequency expressed in Hz hertz.
• R is the resistor value in ohms Ω of the RC timing networks, assuming equal values for both.
• Assuming that both capacitors in the RC timing networks have similar values, C is their farad F value.

Crucial Information:

An approximation is provided by this formula.

The properties of the transistor and other variables may cause a little variation in the actual frequency.

Use simulation software or more complicated formulae that take transistor properties and other circuit components into consideration for more accurate calculations or specific requirements.

When both RC networks have similar values for the resistor and capacitor, the output waveforms duty cycle is around 50%.

Example:

The computed frequency for an astable multivibrator with 10k resistors and 0.01µF capacitors would be:

f = 1 / (1.4 * 10000 * 0.00000001) = 7142.86 Hz (approximately 7.14 kHz)

Note:

Ideal circumstances and component values are assumed by the formula.

To get the ideal frequency and waveform characteristics for your particular signal injector application, you may need to experiment and fine tune.

It is possible to design and construct a BJT astable multivibrator based signal injector that meets your testing requirements by comprehending the formula and the behavior of the circuit.

How to Build:

To build a Simple Signal Injector Circuit you need to follow the below mentioned connection steps:

Assembly Steps:

• Connect base of BC547 transistor to R1 resistor and its collector to R2 resistor and emitter to ground.
• Connect the other BC547 transistors base to C3 capacitor, its collector to R4 resistor and emitter to ground.
• Connect the series of capacitor C1 and C2 one end to R1 resistor and other ends to probe.
• Connect a crocodile clip to negative power supply.
• Connect one leg of capacitor C3 to collector of BC547 and other leg to base of other BC547 transistor.

Safety Precautions:

• Use proper insulation and casing for the circuit to avoid electric shock.
• Do not use high voltage or current that could damage the circuit under test.

Note:

• This basic signal injector can help you inject an audio signal into a circuit for troubleshooting and testing purposes.
• Adjust the frequency of the signal as needed for different types of circuits.

Conclusion:

A signal injector circuit is a valuable tool for testing and troubleshooting electronic circuits.

By injecting a known signal into a circuit under test, it helps identify faults and trace signal paths making it an essential instrument for electronics enthusiasts and professionals.

References:

Signal Injector

signal injector/tracer