You don’t have to be an engineer to be interested in or accomplish something great in circuitry. People all over the world have mastered making their own rendition of walkie-talkies using tin cans, strings, and other unconventional items and materials.
Learning how to make a walkie-talkie could be the perfect craft project for any radio hobbyist, and while nowadays a mobile phone can do anything, this information could come in handy someday. Through this step-by-step guide, you will learn how to create – the heart of any radio device – the circuit that can send and receive signals over a 250-meter radius, using ordinary FM transmitters and FM radios.
What is A Walkie Talkie?
A walkie-talkie is a small, handheld portable two-way radio transceiver used for voice communications. It requires no physical wires connecting the devices.
While they were initially created for military use, due to their outstanding wireless abilities, these devices quickly became popular among the masses. Today, you can find a walkie-talkie app on most smartphones. This app can turn any device (phones, tablets, laptops) into a two-way radio!
A Tin Can Talkie
Most people have some experience with tin can talkies, sometimes called the “tin can phone”. For this, you only need string, and cups or cans. It eliminates the need for a wire, which makes it a great experiment for kids.
All you need to do is to connect either end of the string to the end of both cups. The string placed on the end of the cup can pick up the vibrations from the bottom of the cup, and transfer your voice to the other end. This is sometimes used as a demonstration in schools, and most children are swooned by it.
The ability of the string and the way the string picks up and passes on vibrations just from the bottom of a can is a perfect depiction of how sound travels. The longest string phone recorded was 796 ft long. The string was able to transfer sound without a problem, just like a phone. A string phone like this could be the perfect starting point for children interested in sound waves.
This article goes over how these traditional devices work, and how you can create your own, using simple FM radio parts. To make this specific circuit, you’ll be using an ordinary FM receiver, and an FM transmitter. Anyone you want to communicate with should have the same receiver and transmitter setup. This is a more intricate and complex design than the tin can walkie-talkie, but its design can still be followed and executed by beginners as well.
Before Getting Started
Overall, homemade walkie-talkies are built to have fun. But before diving into the article, people who want to create their very own walkie-talkie circuit need a basic understanding of circuitry. This is not only for safety reasons but for a better experience when trying to put together such an intricate device. It’s no longer about a string and a couple of cans. You’ll be in direct contact with electricity and heat, which when not used correctly can cause fires or shocks.
The most important thing before getting started is finding the perfect workspace for your project. Stay away from flammable objects and other ongoing projects that involve electricity. When working with wires, you should also always be cautious of what you touch and why. If possible, use protective gloves when around wires, and stay alert.
A Walkie Talkie App?
Nowadays everything can be done using your iPhone. Hobbyists today take total advantage of modern technology, relying greatly on their smartphones.
There are multiple apps for circuitry, including an app for design, an app for planning, and so on. Choosing the right one for your interests can be difficult, but the number one app on the market in this area is EveryCircuit. This app is available on most Android phones and can come in handy when creating radio circuits. There are also more and more places to find help when building a circuit.
EasyEDA is the best site for beginners. It’s a free, zero-install web and cloud-based website used by educators, students, and hobbyists. Furthermore, there are multiple articles and videos, even photo demonstrations that help hobbyists master the art of circuitry.
How Does It Work?
I think we’ve all used a walkie-talkie a few times in our lives. Users press the designated button and start speaking through the microphone. As they speak, their voices are converted into radio waves. These waves travel at the speed of light, therefore even by a simple device like this, audio is picked up instantaneously by the other unit. When it reaches the receiving device, the audio is converted back into vibrations or fluctuating electric currents and can be heard through the loudspeaker.
Because the same channel is used by both parties and functions, only one person can talk at a time. After speaking, it’s customary to say the word “over”, letting others know that they’re now free to speak.
Letting go of the “push to talk” button will switch your handset back to receiving mode. With these devices, both parties can send and receive information, unlike most radio devices. This is called two-way radio. The power output of these handheld devices ranges from 0.5-5 watts of power, and even with this lower power output, they can reach decent distances.
Walkie Talkie Base Station
Most handheld devices use base stations (also known as repeaters). These are devices used for communicating with handheld radios. Base stations produce greater wattage output, meaning it grants coverage over a much broader area, but are located in fixed locations.
Often, these base stations are simply mobile radios installed along with a power supply. However, a walkie-talkie does not need a base station to function properly.
There are three communication types users can decide on. These are half-duplex, full-duplex, and simplex. With this circuit, you will be able to utilize half-duplex and full-duplex conversation types depending on the situation.
A solely bi-directional communication type between two people. With half-duplex, only one person can transmit at a time. This is used when you only need to reach someone for a few seconds to tell them something, and then you “switch sides”.
With this mode, both parties can transmit and receive at the same time. A good example of a full-duplex conversation is a phone call, where both people can talk freely without interfering with the other person, and without the use of a button.
The least common mode used, especially by hobbyists. Simplex is a type of one-way communication, such as what radio or TV broadcasts do.
This example of a walkie-talkie circuit is very simple, yet very reliable and durable. The entire circuit is built around the transistor, with an additional few passive parts. Here’s what you’ll need, and how the device is built up.
The Walkie Talkie Circuit
What you’ll need:
Resistors (10K, 4.7K, 15K, and 47 ohms): This is a passive two-terminal electrical part that implements electrical resistance into the circuit. Resistors are used to reduce current flow, divide voltages, adjust signal levels, etc.
- Ground: The Earth’s ground is used as an electrical reference point for circuits. Ground connection doesn’t only protect against electrical shocks but is also used when referring to electromagnetic compatibility, antennas, and various measuring instruments.
Capacitors (10uF and 0.1uF): A passive two-terminal electrical component used to store energy electrostatically.
- Inductor: The inductor is capable of storing electrical energy in the form of magnetic energy.
- Variable and trimmer capacitors: The variable capacitor is used for tuning radios. Its capacitance can be repeatedly changed mechanically or electrically. Trimmer capacitors are also variable capacitors used for the initial calibration of the equipment.
A microphone has to be connected by a wire to a 10K resistor and ground. The audio signal is filtered out by a 10uF capacitor. This allows voice signals to pass, while at the same time blocking interfering signals that may enter.
A 4.7K resistor is also connected to the 10uF to prevent interfering and excess currents reaching the transistor. There should be two resistors (15K and 4.7K) that act as voltage dividers keeping the transistor in active mode when it acts as an amplifier.
Apart from the 10uF, there should also be a 0.1uF capacitor connected parallel to the 4.7K resistor. This will be the “bypass capacitor” that prevents noise from entering the system, by bypassing it to the ground. Usually, it’s connected via a wire between the supply voltage (Vcc) and ground (GND). There are two bypass capacitors, the second one connected across the emitter terminal to pass unwanted high-frequency signals, providing a cleaner transmission.
There’s also a 47-ohm resistor connected to the terminal, which provides stability to the transistor.
Also included in this circuit is a variable capacitor and the inductor from the tank circuit which oscillates between 88 and 108MHz. This will be the device’s range when tuning it to its fixed frequency via the trimmer capacitor.
Finally, there’s a last capacitor that prevents DC noise signals from being transmitted or interfering in any way. The very last thing you’ll need is your antenna, which can be as long as 3 feet to get the best possible range. Without using an antenna, this circuit can reach a maximum of 50-100 meters, depending on the obstacles between the transmitter and the receiver.
Some experienced hobbyists might miss the presence of coils from this circuit. But the simplest circuits don’t need a coil to work. These radio devices and transmitter circuits can be made without the use of a coil.
Of course, a coil can be added, and some parts can be exchanged to coils if you have some you’d like to use. These parts are designed to produce a magnetic field or to provide electrical resistance. There’s also the choke coil which produces inductance.
To be able to switch to full-duplex from half-duplex at chosen times, you’ll need to make a few alterations in the circuit. You need to add a sliding switch, which when turned ON will enable full-duplex mode.
Sliding the same switch OFF will enable half-duplex mode. When in this mode, you’ll need to press the “push to talk” button to transmit voice signals. With these two buttons/switches, you’ll be able to save power when not using the device in full-duplex mode.
You can also add a reliable speaker, for a better user experience. Some people use an external speaker, while others build their speaker into the device. The majority of these devices can work alongside one-pin and two-pin earpieces to make conversation easier. Brands like TOMSENN make one of the most reliable two-pin earpieces and headsets.
With most mobile phones, you can use the built-in radio receiver with your headphone plugged in. This is a great substitute for a speaker in general. Additionally, you can simply use a handheld FM radio as a receiver.
Putting It All Together
Even some of the best walkie talkies out there are using the principles layed out above, so you should feel confident with your passion of putting it all together yourself.
After you made and tested the circuit, you can start using it with friends. Get your FM receiver ready, and tune it to your chosen frequency (one that doesn’t already have a radio station).
Switch your transmission to ON, and using a tiny screwdriver, you can turn the trimmer capacitor left and right until the FM receiver becomes completely silent, meaning that the device has found the right frequency. Now you can start talking through your microphone.
To make the search easier, you can play some music in the background, or talk constantly on the microphone and search for the right sound (just like tuning a radio station).
To test the integrity of the device, repeat this step on a different frequency at least 0.5MHz away from the initial frequency. After testing the clarity of the devices, you can give one unit to a friend and start testing it further from each other. Phones can be used for several things in this process. Some people use their phones as an additional connection during testing, while others use them as a receiver.
After using this article to build your devices bit-by-bit, and after calibrating the maximum range, it’s time to have fun with your walkie-talkie, or even make extras for your other friends in the neighborhood. There are also great ways to alter these devices and experiment with circuitry, discovering new ways to use them, or fun ways to change them. Think like an inventor, and while staying careful, experiment with circuits. It goes without saying that these walkie-talkies are much more fun than tin cans and strings that kids play with.