Simple Walkie Talkie Circuit

This is a basic walkie talkie circuit.

It uses low power to let two people chat over a short distance, kind of like two tin cans connected by string.

But unlike fancy walkie talkies, you can only talk one at a time on this circuit.

Circuit Working:

Parts List:

The article here is a simple walkie talkie circuit.

It uses a single integrated circuit IC the LM386 which is a low power audio amplifier.

Here are the working process of the circuit:

The electret microphone picks up sound waves and converts them into electrical signals.

The transistor BC547 and associated resistors R1, R2, R3 amplify the weak microphone signal.

This switch allows the circuit to function as either a transmitter or a receiver.

In transmit mode the switch connects the amplified audio signal to the choke which acts as an antenna.

In transmit mode the coil generates an electromagnetic field that carries the audio signal.

The strength of the signal depend on the strength of the electrical current passed through the coil which is controlled by the audio amplifier circuit.

When the circuit is in receive mode the selector switch connects antenna coil to the circuit.

Antenna coil picks up electromagnetic signals radio waves carrying audio information from another walkie talkie.

C3 capacitor tunes the receiver circuit to a specific frequency.

Radio waves consist of electromagnetic field with varying strengths.

By tuning the circuit to a specific frequency it can filter out unwanted signal and only amplify those at the desired frequency.

The amplified signal from the receiver circuit is fed into the LM386 audio amplifier chip IC1 which further increases the signal strength.

The amplified audio signal from the LM386 chip is fed to the speaker which converts the electrical signal back into sound waves that you can hear.

A selector switch is a common feature in walkie talkies that allow the user to control when the circuit is in transmit mode.

When the selector switch button is pressed the circuit is switched to transmit mode and the user can speak into the microphone.

When the selector switch button is released the circuit reverts to receive mode allowing the user to hear incoming transmissions.

This is a simple circuit and will likely have a short range on the order of tens of meters depending on the environment.

How to build the antenna coil:

The most important part in this circuit is played by coil below are the process to build the coil.

The coil connected to the collector of transistor T1 BC547 acts as the antenna coil.

We will build this coil using a premade adjustable inductor slug as given in diagram.

The slug is approximately 3mm in diameter and 7 to 10mm tall.

Wire: 

• We will use super enameled copper wire with a diameter of 0.3mm to 0.5mm.

Winding: 

• Start by winding 4 turns directly onto the slug.
• This will be the primary coil.

Secondary Coil: 

• After completing the primary coil, carefully wind 2 turns additional turns directly on top of the existing primary coil.
• This creates the secondary coil.
• In the secondary winding take out a wire tap after 1 turn from the bottom side and connect it with capacitor C6.

Formulas:

A walkie talkie circuits frequency is determined by a number of variables, chief among them being the design of the oscillator circuit that produces the carrier frequency.

To create a steady carrier frequency, walkie talkies usually employ an LC oscillator or a crystal oscillator.

The oscillator circuits component parts dictate the oscillation frequency.

Here is a simple explanation of the formula that applies and how the frequency is calculated

The frequency f of a simple LC oscillator circuit is determined by:

f = 1​ / 2π√LC​

where,

• L is the coils or antennas inductance measured in henries H.
• The capacitance of the capacitor is expressed in farads F as C.

Note:

A phase locked loop PLL circuit and a reference oscillator are commonly used in frequency synthesizers to identify the frequency, providing accurate control and stability over a variety of frequencies.

The oscillator circuit utilized whether it be an LC oscillator, a crystal oscillator or a component of a frequency synthesis system determines the precise frequency of a walkie talkie circuit.

A fundamental grasp of frequency calculation in an LC oscillator system is provided by the formula.

How to Build:

To build a Simple Walkie Talkie Circuit you need to follow the below mentioned components connections steps:

• Connect pin 1 and 5 of IC LM386 together with capacitor C10.
• Connect pin 2 and 4 of IC LM386 to ground.
• Connect pin 3 of IC LM386 with capacitor C9.
• Connect pin 5 of IC LM386 to ground in series with capacitor C11, 8 ohm speaker and a selector switch.
• Connect pin 6 of IC LM386 to positive supply.
• Connect emitter of transistor T1 BC547 to ground with resistor R4.
• Connect base of transistor T1 BC547 with selector switch.
• Connect collector of transistor T1 BC547 to one leg of antenna coil.
• Electret Mic one end is connected capacitor C7 and other end to ground.
• ON/OFF switch is connected to positive supply of 6V battery.
• Antenna coil one leg is connected to 22uH choke and a antenna.
• Connect one leg of antenna coil to capacitor C1, C2, C3 and resistor R1 and R2.

Note:

• Be sure to follow safe electronics assembly practices when building this circuit.
• Keep in mind that building a walkie talkie requires some knowledge of electronics and soldering skills.
• There are also legal regulations regarding radio transmission power depending on your location.

Conclusion:

Building a simple walkie talkie circuit is a fun electronics project that can introduce you to basic circuit design and radio communication concepts.

However, it has limitations if you are looking for a long range, full duplex walkie talkie experience this is not the solution.

However, for a basic learning experience or for short range communication in controlled environments this can be a great project.

References:

Walkie-talkie

Datasheet IC LM386