Simple Walkie Talkie - Complete Circuit Diagram with Design Details

The article explains a simple walkie talkie circuit that can be easily built by any hobbyist and used for communicating between rooms or floors or simply for having some fun across neighbors and friends. The range of this system is around 30 meters.

Simulation and Working


The figure shows a four stage transistorized circuit which behaves both like a transmitter and a receiver unit, making the design very economical and versatile.

An ordinary “4-pole double throw” switch serves the purpose well for transforming the unit either to a transmitter or a receiver while communicating with another identical transmitter/receiver set.

As can be seen in the diagram three transistors are directly coupled for making an audio amplifier stage set to operate at a significantly high gain.

The first transistor functions as a pre-amplifier which pulls the minute voice signals to some higher level and feeds to the next high gain Darlington stage which further amplifies the received audio frequencies and dumps it across the primary of a driver transformer.

How Driver Transformer Works


The driver transformer steps up the level of the signals such that it becomes clearly audible over the connected loudspeaker.

The speaker may be salvaged from an old small transistor radio or from a landline phone (earpice).

The speaker in the shown design is configured in an interesting manner. Depending upon the position of the walkie talkie switch, the speaker works like a sound reproducer when it’s in the receiver mode and like a super dynamic microphone when the switch is toggled in the transmitter mode.

While the speaker is being used as a sound reproducer or simply in the receiver mode, the first transistor acts like a signal receiver, picking up the audio across the 4k7 load resistor through the 0.47uF capacitor.

The signals then has to pass through a connected volume control stage to finally reach the three transistor amplifier stage discussed above.

However while the proposed walkie talkie circuit is flipped in the transmitter mode, the speaker gets rigged right at the input of the amplifier stage such that the spoken voice hits the speaker diaphragm and gets amplified by the same transistor stage.

This amplified voice signal is now applied in the form of supply voltage for the circuit in the transmitter mode. The switch also makes sure that the 27 MHz crystal gets connected with the first stage while the transistor gain is uplifted by eliminating the 390 ohm resistor and using a 59 ohm resistor at the emitter of the transistor.

In the transmitter mode the speaker transformer secondary now has no connection with the voltage step-up function rather simply acts like a series inductor for coupling the output of the audio amplifier with the supply rail and for sending the signal across the winding to the transmitter stage in the form of a fluctuating supply voltage.

As the above signal witnesses a rise and fall in response to the spoken voice, the gain of the first transistor stage is forced to change correspondingly which in turn results in a varying amplitude for the carrier waves transmitted by this stage over the attached antenna.

Thus the spoken voice now gets converted to an amplitude modulated (AM) RF 27MHz signal which may be picked by another identical unit placed in the vicinity for the same reason.




Parts List


All resistors are 1/4 watt 5% CFR

100 ohm - 1
220 ohm - 1
5.6K - 1
4.7K - 1
3.9K - 1
1M - 1
15K - 1
33K - 1
56 ohms - 1
390 ohms - 1
10 k preset - 1

Capacitors Electrolytic

33uF/25V
100uF/25V

Capacitors ceramic disc

0.47uF - 1
22nF -2
220pF- 1
4.7nF - 2
10nF - 2
82pF - 1
33pF - 1
15pF - 1
39nF - 1

Transistors

BC547 - 2
BC338 - 1

Miscellaneous

Crystal 27MHz - 1

TPTT 3 pole triple throw switch - 1
Audio transformer - 1
small speaker 8 ohm 1 watt - 1
9V battery - 1
Inductor as explained below

How to Wind the Antenna Coil


The coil associated with T1 is the antenna coil. It is constructed over a ready made variable inductor slug (see image below) having an approximate 3mm diameter and around 7 to 10mm height.



The wire used is a 0.3 to 0.5mm super enameled copper.

Start with the primary 9 turns first, directly on this wind the secondary 2 turns.

The coil in series with the antenna is s simple air core coil made by winding 5 turns of 0.3mm with 5mm diameter.

How to Wind the speaker coil


You may use a small audio transformer for the shown speaker transformer, or alternatively build it by winding around 70 turns for the primary (left side), and 500 turns at the secondary (speaker side).

The wire may be a 0.2mm super enameled copper wire wound over a 3 inch long iron screw.

How to Set up the Circuit


After you have built the above explained walkie talkie circuit it's time to check its response by powering it with a 9V PP3 battery.

Initially let the switch contacts be positioned for activating the transmitter stage.

For knowing whether the transmitter is generating the required 27MHz frequencies or not you will first need to make an RF sniffer circuit as explained HERE

Switch ON both the circuits, position the above RF detector circuit about 10 inches away from the walkie talkie antenna, and begin adjusting its variable inductor slug gently using an insulated screw driver which are typically used for adjusting FM radio GANG trimmers.

If every thing's done correctly you'll hopefully see the RF detector LED glowing brightly at some point of the adjustment process.

Seal and glue the variable inductor at this position, and you can assume your walkie talkie to be all set for having some great time with your friends.

However you would need to build another identical set for exchanging the conversations with the other guy, otherwise a single unit wouldn't have much of an importance.

Need Help? Please send your queries through Comments for quick replies!




Comments

This what I've been waiting for!!! thank a looooot Swagatam!!!
ABDUL AZEEZ said…
hi sir,

Thank u so much for this circuit. i m very happy.
Swagatam said…
you are welcome eshkariel.
Swagatam said…
My pleasure Abdul...
Pritesh kumar said…
Sir, I am very happy to seeing this circuit.But sir i want to control reciever and transmeter only one switch.please describe about this.
Pritesh kumar said…
SIR, How to i change its range please describe.
Pritesh kumar said…
sir what is 27MHs crystal.
Swagatam said…
Pritesh, the four switches which are shown in the diagram are the parts of a single 4PDT switch, meaning you will have only one switch to toggle which will enable all the four contacts to move together inside the switch....
Swagatam said…
increase the antenna length, it will help to improve the range
Swagatam said…
please Google it online you will get a lot of info regarding its function and appearance.
Jeremiah Ballos said…
sir what is the setting frequency for this walkie talkie? can it 88MHz to 108MHz? sorry for my bad english..
Swagatam said…
jeremiah, it's actually a 27MHz system
Swagatam said…
...88 to 108 MHz will require a lot of tweaking...not recommended.
Mark Aala said…
Hi. Im very happy with this circuit. Thank you. I do have a question. What is the type or specifications of the transformers used? Please let me know. Thanks.
Swagatam said…
Hi thanks, the winding data for the transformers are explained in the article, please refer to it.
Mark Aala said…
I do get it now. Thanks a lot bro
Mark Aala said…
Hi. Its me again. Just for clarification, a walkie talkie is a half-duplex wireless intercom right? Thanks.
Mark Aala said…
Hi. I do have a question again. Sorry for having lots of questions. Just due to curiosity.

Which in the circuit acts as the microphone? Because looking in the circuit, there is no such a microphone component. Thank you.
Swagatam said…
Hi, when the switch is flipped towards Tx the speaker is transformed into a mic, i think i have mentioned this in the article itself
Neeraj B A said…
Sir what all modification is to be done in this circuit to increase the range approximately up to 500m
Swagatam said…
Neeraj, it would be difficult to accommodate more power in this basic design, more complex stages might be required for implementing this.
afnan ahmed said…
sir plz tell me about the power of transformer
afnan ahmed said…
sir what is the diameter of 3 inch long screw
Swagatam said…
a 5mm thick core will do
Phalguna Pandu said…
Sir,can u name the antenna
Swagatam said…
the antenna can be just a meter long wire or if possible a telescopic type of antenna.
Phalguna Pandu said…
Sir,we are unable to get inductor slug ,so please tell how to wind the antenna coil and more over what do you mean by air Cole coil?
Swagatam said…
Phalguna, the slug type inductor will allow you to adjust and set the frequency easily with a screwdriver, without this it would be extremely difficult and confusing to set the circuit so it's recommended to use a slug type coil only.

air core coil means, a coil built without the need of any core or with an empty core.
Swagatam said…
please see the second image, it's a coil wound over a plastic former with a threaded screw system at the center for facilitating the screw in and out of the core using a screw driver.
how does RF sniffer circuit can be used for this project?
we are not able to find inductor slug in outside stores
Swagatam said…
without a slug inductor it would difficult to set the frequency of the unit.....RF sniffers are used for identifying an RF presence........it won't tell you about the frequency value
Carlos Origenes said…
Hello! what should be the wattage rating of the 8ohm speaker? Would a regular 10k potentiometer be a viable substitute for the 10k preset? Thanks
Swagatam said…
Hi, the speaker can be any ordinary 8 ohm small speaker, wattage can be of any value.

yes a pot can be effectively used in place of the shown preset.
Carlos Origenes said…
thanks for the reply sir! :)
would it be possible to add indicator LEDs to the circuit for on/off and transmitter mode without affecting the voltages and currents that much?
I am still unable to find a variable inductor slug :( would it be possible to make one using an iron nail or bolt? Do I still need to insulate the core with plastic?
Thank you so much
Swagatam said…
Carlos, I can't see any spot in the existing design where an LED could be accommodated without disturbing the circuit's performance, the only way could be to upgrade the changeover switch with an additional pair of contacts, so that this contact can be used for integrating a couple of LEDs for the required indications.
Carlos Origenes said…
Oh. If that's the case then I won't bother adding the LEDs. I have quite a big problem :( I can't find a BC338 transistor, so far. The stores I've visited only have BC337. Would it be okay to substitue the BC337 to the BC338?

I've checked their datasheets but I still can't decide

Sorry for asking so many questions :( I am planning on making this project for our prototyping class. Our professor asked us to search for a circuit online to build and this really caught my attention. Sorry for the trouble
Swagatam said…
BC337 can be replaced with BC338, but please note that this circuit requires some good knowledge and skillful hands for the setting up procedure, and this is not for the newcomers, and everything is too critical in the design, even a smallest of faults will stop the circuit from working....try it only if you have built similar circuit in the past and have good experience with RF circuits.
joao said…
Hello , you already implemented this circuit do that this way , and it worked ?
Swagatam said…
I have not yet tested it....
joao said…
hello , I will try to do this project , but I have some doubts .

1 - the variable inductor , I can do it ? I could not find a piece to make it. I have a part for variable inductor but with 6mm diameter , can I use this piece to make it ? The number of turns on it will be the same ?

2 - to the speaker of the transformer, I plan to use a screw with 3 inches. But how should I do? I do the 500 secondary turns of the screw and then put a tape to isolate and make the 70 laps of the primary ?

thank you
Swagatam said…
1) 6mm will do. and the same coil specs can be used with this diameter too.

2) you'll have to use an audio transformer for the speaker coil....a homemade screw wound coil might not work
Yael Corona said…
Hi Swagatam!!

Thanks for the design, I only have a question, is this circuit transmitting in FM?
Swagatam said…
Hi Yael, yes it's an FM transmitter/receiver circuit
Yael Corona said…
Hey man thanks for reply and congrats your blog is great..

:D
Swagatam said…
you are welcome yael!
Shameeh S said…
sir what is the no.of turns for the second transformer ??
Swagatam said…
It could be around 10:1000 turns, better to go for a readymade audio transformer
Alex Malik said…
Can you please explain how to wind speaker (if you're doing it on your own) show me some pics... it will be more helpful
Swagatam said…
sorry, I have never wound a speaker, so have no idea about it.
ashish kher said…
any simpler circuit for walkie talkie ?
Swagatam said…
buy two FM mics with different frequencies and two FM radios, and you can communicate across these units
Narendra Singh said…
Sir, i wanna to get its equipments... Becoz it is so much good for me... So plz sir, tell me briefly about its equipments... Thanks sir
paul oo said…
Do you have EagleCAD or PCB pictures/files to view? I'm curious about the form factor as well (SolidWorks files?)
Unknown said…
Thank you sir for this circuit but I have a question if you may
It's about the Antenna Coil ( 0.3 to 0.5mm super enameled copper with primary 9 turns and secondary 2 turns )
what core should I use to wound over ?

Also the coil in series with the antenna ( 5 turns of 0.3mm with 5mm diameter )
what core should I use to wound over also ?
Please explain :) thanks
Swagatam said…
for the antenna coil use an iron screw as the core which can be moved up down as shown in the second diagram.

for the antenna series coil no core is required
Swagatam said…
walkie taikie is a difficult project you must first know all the basics of RF transmitter receiver concepts
Demetrio Olarte said…
how does the speaker acts as a microphone?
NIRANT RAUT said…
i want to make simple walky talky circuit for my project at collge. can u plz help me out for it
NIRANT RAUT said…
hi sir.. I want to know some things about fm trasmitter
Swagatam said…
If you have any specific question about it, you can ask... I'll try to answer
Demetrio Olarte said…
Sir, what color of the audio transformer should be used?
Swagatam said…
You can try a 24MHz, it could just work.

the transformer could be as shown below:

https://cdn.instructables.com/FA8/YZ4S/FP8NL8P0/FA8YZ4SFP8NL8P0.LARGE.jpg

rest you can search and learn from the internet.
Akash Hulke said…
Thank you sir, but what is rating of transformer use near speaker in circuit. And the transformer near antenna 9turns-2turns what is this exactly, what do I need to do exactly here.
Akash Hulke said…
also sir, if I use 24Mz crystal, then do we need to do changes in sniffer circuit. If yes then which?
Swagatam said…
For the antenna coil details please refer to the section
"How to Wind the Antenna Coil"

the speaker transformer is called "audio output transformer", the wattage is not important, It was popularly used in old AM transistor radios near the speaker.
Swagatam said…
if you are not familiar with RF transmitter circuit then you should not try this circuit. you should first practice with smaller circuits as explained below

https://homemade-circuits.com/2014/08/spy-bug-circuits.html
Akash Hulke said…
Sir,I didn't get 9turns- 2 turns transformer, which is associated with collector of first transistor.
What to do now?, it isn't available in market near me.
Swagatam said…
Akash, the transmitter coils will need to be built at home.....

if you are not familiar with RF transmitter circuit then you should not try this circuit. you should first practice with smaller circuits as explained below

https://homemade-circuits.com/2014/08/spy-bug-circuits.html
Akash Hulke said…
Sir, walkie talkie is my engineering project, I will study circuit provided in the link. But my question is,
Can I use IFT in place of that 9turns-2turns transformer.
I tried it and didn't get anything on sniffer circuit.
Can you please tell me how to troubleshoot the circuit I made.
Swagatam said…
IFT will not work, the core needs to be iron screw type, and the number of turns and diameter must be exactly as mentioned in the diagram.
Akash Hulke said…
So,I need to wound 9turns on one end of screw and 2turns on other end. Am I right?
But sir, can I use the wire, which is use in Motor windings?

Sir, we are giving 9V dc supply to the circuit and know that transformers only work on AC, so how audio transformer in the given circuit works.
Swagatam said…
No, the screw needs to be movable across the coil length so that it can be moved and adjusted up/down with a screw driver....

Motor winding wire will not work,,,,it has to be thicker, around 22SWG

The audio transformer is working with an oscillating DC signal, not with a stable DC.
Akash Hulke said…
Sir, can you show me any picture of that winding on screw, at least a drawing or anything, so I can I can get idea of it or please describe it a little more.
Swagatam said…
Akash, please see the second diagram from top, the coil can be seen wound over a plastic bobbin consisting of a central iron screw, this iron screw can moved up/down using a screw driver
Akash Hulke said…
Sir, there is only one winding over bobbin, where is the secondary winding?
Swagatam said…
the picture is only for example purpose it's not the actual image of the coil....the second smaller winding can be wound over the first larger winding
Akash Hulke said…
Sir, can you please tell me exactly, what should I do?, this is the only thing now, stopping me in this project.
Akash Hulke said…
Nobody is able to help me in that thing,even my teachers
Swagatam said…
the design can be modified differently so that it works with a single coil but that will require an expertise and a thorough knwoledge regarding RF transmitter circuits....

anther option would be to buy a ready-made walkie-talkie and then duplicate it by procuring the exact same parts.
Akash Hulke said…
ok,I will make one more try for that coil, if I find any difficulty, i will ask you.
One little question,
Are the values of components fix or can be change little, like I didn't get 15pF capacitor, they gave me 18pF, is this ok?
Swagatam said…
slight changes will do which will need to be later on compensated by adjusting the coil dimensions
Esraa Shahin said…
its really a well design , but I want to ask you what's the type of antenna did you use here ? and if you know an easy program to simulate it, please ?
Swagatam said…
thank you, a 6 inches wire will be enough to work like an antenna...
Sir can you help me to design with carrier wave of 455khz
Swagatam said…
you will have to modify the antenna coil and the associated capacitor along with the crystal suitably...
Sir Pls I Have A Project Work Of Building A Walkie Talkie Of Range 500meter,how Can I Reduce A 2km Walkie Talkie To 500meter Range.Thanks
Swagatam said…
Christian, you can do it by changing the antenna with a mismatched antenna, or simply reduce the dimension of the antenna.

the other technique is to reduce the supply voltage, or the supply current
Unknown said…
Sir.. My brother gave me a task to do walkitalki.... Can you please help me sir.. How to do it??
Jacob Mathew said…
sir, may i know what is 39n ?? there is no 39 nF capacitor that i can find... and how to do this project with a standard double throw switch ??
Jacob Mathew said…
sir and if its it not too much to ask, can you upload all the parts list ?? especially the technical names of the transformers and antennae ??
Jacob Mathew said…
also sir, can you please point out where the inductor slug and audio transformer is on the circuit...
Swagatam said…
you can use 33nF instead of two 18nF in parallel.
Swagatam said…
inductor with slug is on the left side with BC547 transistor....audio trafo is at the right side

build it only if you are reasonably expert and have previous experience with practical Rf transmitter circuits, otherwise you might fail in getting the results and end up wasting money and time
Swagatam said…
it is at the base of T1...click the diagram to enlarge.
Chris Wang said…
Hello, have you built and tested this circuit? If so, how well does this work?
Swagatam said…
Hello, This circuit was drawn by referring to a commercial unit's PCB, so it is a tested design.
Chris Wang said…
Would you say it is feasible to create this circuit on a breadboard and fit inside a custom 3D printed case? Or would creating one's own PCB be more convenient?
Swagatam said…
breadboard will not do...it will need to be built over a neatly designed PCB, and tweaked accurately by an expert having a sound experience with RF circuits
Chris Wang said…
what is your opinion on using a stripboard instead?
Chris Wang said…
also what is your reasoning on why a breadboard will not work? what if we do not try to create a case for it?
Swagatam said…
RF circuits must be tightly built with minimum wiring otherwise it would fail to oscillate and stop working, that's why breadboard cannot be used.
stripboard is OK but the soldering and the connections must be done extremely efficiently.
olupot said…
hi sir this circuit looks interesting for its alot of fun but i would want one which transrecieves for both audio and video if possible. that can transmitte and recieve both audio and video from another room thanks
Swagatam said…
thanks olupot, presently I do not have the requested circuit so can't say much about its details, if possible I may try to find one and publish here
olupot said…
i will be waiting sir i apperciate your efforts
Coleen said…
Hi Sr.! Could you post a video in testing this circuit??
Swag said…
Hi Coleen, sorry that won't be possible presently...
coleen said…
okay Sr., I understand... I just have another question, Did you try this walkie-talkie circuit by yourself Sir?
Swag said…
I found the schematic inside a readymade walkie talkie package, which was purchased by one of my friends and the model was tested to be perfectly working.
coleen said…
Thank you sir :)
Swag said…
you are welcome!
bambang prayogi said…
Is that toy walkie talkie circuit?
Swag said…
Yes it is a toy, with relatively smaller range!
Chloe Lemaire said…
How can I modify this circuit to be wired instead of wireless? Also can it be possible to create a Master Slave circuit consisting of 3 slaves?
Swag said…
The concept explained on the top section of this article: https://www.homemade-circuits.com/spy-bug-circuits/ discusses a wired system, you could refer the first concept and build the basic design from the given information
Chloe Lemaire said…
So I simply remove the circuit after the Transmitter-Receiver Switch and replace it with a wire? Thanks~
Swag said…
actually I was referring to the following article:

https://www.homemade-circuits.com/spy-bug-circuits/

you can use the first circuit, and connect its output with any audio amplifier placed at the receiving end
Chloe Lemaire said…
Lastly, would it be okay if I change the Driver Transformer into a amplifier for the mic/speaker? Since I really like the way speaker converts into a mic.

~BTW, thanks for the link you provided since it helps me a lot considering it only consist of discrete parts.
Swag said…
For the above walkie talkie design, I won't recommend any changes, it has to be exactly as indicated.
I am glad the linked concept helped you, keep up the good work.
Solomon said…
Hello Sir, This Is A Nice And Interesting Circuit, But Is It Tested And Worked
Swag said…
Thanks solomon, yes it is a tested design, however being a complex RF circuit it is recommended only for those who have thorough knowledge of RF theory and have worked with practical RF designs.
Karthik said…
Hi .. I didn't have old telephone speaker ....so what I should do ..what type of speaker I should buy in shop
Karthik said…
Sir please make a list of all parts I should collect ...this is small request ....!! And I didn't have old telephone speaker so..what I should use in place of it
Swag said…
Hello Karthik, I did not test the design myself so I cannot say anything with assurance, but I'll try to update the parts list soon.
Karthik said…
Thanks for reply.....
And please make it soon and give me a idea plzz.
gwapa said…
hey sir what simulation software did you use?

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