The article explains a very simple circuit of a wireless speaker system which can be used for playing hi quality music wirelessly from your TV set, DVD player, Ipod, cell phone or from any music system.The speaker thus can be placed in any corner of the house within a radial distance of 50 meters and high quality music can be enjoyed without the hassles of long connecting wires.
For implementing the entire wireless speaker system, we actually need to make two sets of circuits, a transmitter circuit for transmitting the music signal from the source input as discussed above and a receiver circuit for receiving the transmitted music signal and for playing it in the attached speaker.
Transmitter Circuit:
As shown in the figure, the configuration looks a little different from the usual single transistor transmitter circuits where a single stage is used for the audio amplification and for the generation of the modulated carrier waves.
The usual single transistor transmitter circuit has the advantage of smaller and compact size and minimal power consumption, but is not suitable for long and strong signal transmissions.
However since such circuits are commonly used for wireless, stage-microphone applications, the distance is not a factor but compactness and low power consumption is definitely a must, and therefore becomes quite suitable for the intended application.
The present design is not intended for the above application so the first two features are not important, however the proposed idea of a wireless speaker system surely requires a long range and a distortion free power transmission, so that the reception can be heard at any corner of a particular premise or even across an apartment.
Therefore a stronger signaling or transmission of stronger carries RF signals becomes a necessity.
That’s exactly why we have incorporated a couple of extra stages in addition to the central carrier wave generator stage.
The first transistor and its associated components form a neat little audio amplifier stage and also a buffer between the audio source and the transmitter circuit.
This stage amplifies the received signal to stronger levels, and this stage also allows keeping the volume of the source signal to minimum levels.
The amplified signal is passed on to the next stage, which is the actual RF signal generator stage.
This stage is basically a simple feedback type of oscillator, wired to produce RF signals in the range of around 90 to 100 Mhz.
The amplified signal from the collector T1 start forces T2 to modulate the generated RF with the injected audio signals.
The modulated signal from the collector of T2 can also be directly used for the intended wireless music receiving, however since we are interested in making it more powerful, we introduce another stage which becomes responsible for amplifying the modulated signals to much stronger levels so that it may be heard across many 10s of meters away and even in cell phone radios.
The whole transmitter circuit can be built over a small piece of veroboard and housed inside a suitable sized metal box along with the required power supply section enclosed.
This concludes the transmitter circuit.
The Receiver Circuit
Ideally you won’t need to build this as the receptions can be heard crystal clear over an ordinary FM radio set. Therefore you might just want to use the FM radio itself as the wireless loudspeaker, or probably add an ampli-speaker box in conjunction to you FM receiver.
That’s it, your wireless speaker box system is ready and may be used for listening to any audio transmission without connecting wires across a radial distance of more than 50 meters, if the antenna is made large enough, the range may be well increased to beyond 90 meters.
Parts List
R1 =1M,
R2 = 2K2,
R3 = 470 Ohms,
R4 = 39K,
R5 = 470 Ohms,
C1 = 0.1 uF,
C2 = 4.7 uF,
C3, C6 = 0.001uF,
C4 = 3.3pF,
C5 = 10pF,
C7 = 100uF/16V
D1----D4 = 1N4007
L1 = See Text
T1, T2 = BC547B,
T3 = BC557B
TR1 = transformer, 0-9V, 100mA
Raj Mukherji says
Hi Swagatam,
First let me wish you a "Wonderful 2012".
Since, I have not yet made any progress with the FM wireless switch (mainly with the transmitter part), therefore, thinking that the single transistor transmitter circuit which you had provided is not delivering enough range and clarity, I wish to construct the 3 transistor circuit which you have explained here.
However, in the third last paragraph of your blog, you have suggested to use a "1mm super enameled copper wire". Now, if you refer to the following URL, you will see that an 18 SWG has a diameter of 1.219mm while a 19 SWG wire has a diameter of 1.016mm. Therefore, will I get the same result from either of those two wires? This is important for me to understand because in your blog you have clearly mentioned: "The inductor L1 is the most critical part of the circuit" and that so far I have tried various ways to design my FM transmitter (referring your earlier circuits) and only could manage to hear a feeble UM66 music on my cell phone FM radio at a distance of about 6 inches from a 3 feet long telescopic antenna!!
Here is the URL for your reference:-
http://en.wikipedia.org/wiki/Standard_wire_gauge
Waiting to hear from you soon.
Regards,
Raj
Anonymous says
What's the frequency of the circuit?
Anonymous says
Well, I'm having a problem. I can't get it working. I think the connections I made are correct, but I get no sound. I have soldered a 3.5mm audio socket on the pcb and I connect this to a laptop using a male-to-male audio cable. I am not using a transformer, so I removed the diodes and I only left the C7. For the tap on the air coil I scratched the top of the second turn and I soldered a thin wire on there to connect it with the capacitor. I don't know what's wrong. How can I find out what's the right frequency when I search between 90-100MHz? Will I hear any specific sound that indicates thet the circuit is transmitting? Also I would like to know what's the length of the antenna.
Thank you in advance!
Sotos (ex-Anonymous) says
Swagatam thank you very much for your help. Here are some more questions I have on the particular issue.
I think that I found the frequency. I don't actually get a null spot, but this is the most "ticklish" frequency of all between 90 and 100MHz. What I mean is that when I tweak the coil I hear some changes in the sound or I get a null spot, but it is very momentary. Also I think my antenna is not right. I used a 30cm regular wire with plastic insulation. So my questions are
1)How can I fix the transmission frequency and
2)How to make the antenna.
Sotos says
All done, but there is sth peculiar going on. I can get the null spot on 93.3Mhz and on 108.0MHz as well. Is this right? Also when I connect the audio cable I completely lose the null spot and it's like the transmitter isn't working at all. Also, after the connection of the cable, I can't trace again the null spot. After some effort, I managed to hear sth on the radio but it wash very fade with a lot of jamming going on. In order to get this awfull result I had to give a really strong audio signal. If I had tried to disconnect the cable from the circuit and connect it to my speakers, the whole neighbourhood would have heard that. It is also worth mentioning the fact that it was impossible to connect the C6 with the coil. If I had done so, I would have never been able to hear anything.
Sotos says
Success! I get a perfect quality sound but there still some… "gaps". First of all, I find it impossible to connect the C6 to the coil. Every time I do that, the signal fails. Also, I noticed that the device is very sensitive. I can't move it or pass in front of it without jamming the signal. Do you think there is sth wrong with my antenna. My wire is wrapped around and tighten with the excess wire in a shape that looks like number eight. By the way! I just realised how PERFECT the circuit is. The fact that there is a built-in audio amplifier allows me to provide a really low level of sound, which also saves a lot of energy!
Anonymous says
Hi, am from Kenya.I am a high sch. Level student.I kindly would like to know where I can get the items need to make the wireless transmmitter.Do i ask for them in an electronic shop as you have listed or they have specified names. Thanks lol.
rishabh jain says
hlo, sir i am making a remote control jammer,in which i take silver wire,bt my circuit is not working,please help me,nd can u tell me how i see my ir led is it working or not some one suggest me watch it my digi cam is it true,please sort out my problem,nd reply me on my mail address
careless12892@gmail.com
rishabh jain says
hlo,sir am making a remote control jammer,in which i face a problem,i m using silver wire as jumper,is it necessary to use only copper wire on breadboard,nd i how i see my infrared led is working or not?led longer leg is postive?
rishabh jain says
sir,can u explain how i tested through receiver circuit using ir sensor?
nobert singh says
can you provide us a wireless webacm circuit too so that we can connect this wireless speakers with a toy car and can make a wireless spy car ! can you recomend us how to add battery in the transmitter circuit instead of AC mains. can i use an anderoid mobile phone to hear the voice instead of the FM the mobile have the facility to adjust frequency too. Can we make the frequency more high so that we can use it for log distance ?
Thanz in advance.
Pradeep Raj says
Thank u so much sir… I like all your articles…
Pradeep Raj says
Siur, How to fing positive terminal in ceramic capacitors..
Mainak Sarkar says
hello sir i am very great full to you, my father hd also made it many years ago. but now your circuit help him a lot to remember.
jake says
hi sir can you post actual video or pictures of the device???
if possible in youtube
Swagatam says
Hi Jake,
I did this project many years ago, if i get a chance to do it again then surely i'll remember to put it on utube.
Juls says
hi sir, kindly explain why is it that the antenna is connected at the collector of the last amplifier stage??.
Swagatam says
Hi Juls,
Collector of a transistor is the place where the current gain is at the maximum level, therefore to transmit maximum signal into the air the antenna has been connected at that point.
Juls says
Hi Sir,thanks for the previous reply. Kindly suggest some techniques to minimize the noise on the said project. We tried making the project and it works just that there is distortion on the output.
Swagatam says
Hi Juls, in my prototype the noise was zero.
It might be due to input stray pick up. The input pin should be directly connected to C1 and the whole circuit should get connected to the input jack of the signal source, meaning their shouldn't be long wire from C1, because this will pick noise and will be amplified by the transmitter.
Also the power supply should be 9V and not more than that, and should be highly filtered, preferably a battery should be used for minimizing noise.
Sharjeel Faisal says
Sir can u plz help in increasing a single length that how i am able to increase the length of the signals….?
Thank u very much for sharing ur idea with us thank u very very much sir…
Swagatam says
The range cannot be increased with simple modifications, the circuit will need major modifications which would be difficult for you to make….
Sharjeel Faisal says
sir how to increase the length of the signals…?
and thanks for the gr8 idea…!!!!1
Sharjeel Faisal says
sir i used the copper wire which is used in cable tv as L1 is that ok and what should be the distance b/w the consecutive turns?
Swagatam says
cable wire copper wire will not be appropriate because it's not insulated, if the turns touch each other, the transmitter won't work.
The wire should be closely wound and therefore should be a super enameled type.
Sharjeel Faisal says
sir as u told us before that first make central part of the circuit than check for the null spot bw 90 to 100 mhz
than sir i have made that section bw there is not any null spot in fm radio…
is there any condition for that..?
And thank u very very much for reply my all queries..!!!
Swagatam says
The coil is the critical part, if have not made the coil correctly, the circuit will not work.
Sharjeel Faisal says
is this necessary to use 100mA transformer instead of 350mA…?
Swagatam says
100 ma….350 ma both will work
Sharjeel Faisal says
thank u very very much for every rep….sir
Anonymous says
How can I tune my cellphone TM radio with my transmitted signal by this circuit?
Swagatam says
If the circuit is built correctly, your cell phone will be able to catch the signals even from 10 meters away.
I could catch the signals crystal clear on my cell phone from a distance of 10 meters.
Anonymous says
I mean to say for cellphone FM radio I have to tune the signal in terms of MHz so by which number can I tune it? (ex. Radio mirchi 98.3 Mhz)
Swagatam says
This circuit will not catch stations, it will transmit any music that's fed at its input….. probably I still did not understand your question.
Anonymous says
Suppose I have made this transmitter ckt. Now I want to recieve the signals from this ckt to my cellphone FM Radio. So with which freq I have to tune my cellphone FM radio so that I can recieve the signals from transmitter ckt shown here.
Transmitter: ckt described here in this article
Reciever: Cellphone FM Radio
Tune freq in cellphone FM radio=???
Swagatam says
You will have to search it because the transmitted frequency will be unknown, or you can first use an ordinary FM radio for locating the frequency of transmission and then tune your cell phone around that MHz.
However it can be simply done through manual searching by standing at close range to the transmitter.
Anonymous says
hello sir , how r u?
i m interested in making homade sound system with hifi woofer, as high quality of sound as possible to my level with easy circuit,i m just more than a begineer,
can u help me in this matter? or any recommended circuit
thnx a lot
Swagatam says
You can make the following circuit, it's the easiest, the best, Hi-Fi and very powerful:
https://homemade-circuits.com/2012/04/how-to-make-simplest-100-watt-mosfet.html
https://homemade-circuits.com/2012/05/home-made100-watt-mosfet-power.html
Anonymous says
hello sir,
could u please explain the requirements of the inductor used in the circuit and what are the steps i have to taken for connecting the inductor in the circuit?
Swagatam says
Please refer to this link:
http://www.sm0vpo.com/tx/bug5.htm
Anonymous says
hello sir,
is there any problem to increase the leg length of the inductor coil used in this circuit and what are the requirements of inductor in it?
Swagatam says
Disturbing the length of the inductor would drastically disturb the frequency, and the transmitter wouldn't work over the radio FM band.
please refer to the above comment link
Anonymous says
Hi sir,
Thank u for your great help to make this circuit easier.Kindly explain me the use of capacitors C2,C4 and C6 used in this circuit.
Swagatam says
C2 is for filtering any residual ripple in the supply voltage.
C4 is the part of the tank circuit which is involved in generating the carrier frequency
C6 is the blocking capacitor which prevents DC from entering the preceding transistor stage.
Anonymous says
Thank you sir for the previous replies which help me a lot
Hemanga says
Is main AC should be 230V or 110V?
Swagatam says
as per country specs.
Akki Sankpal says
the dimensions u mentioned about L1 can u elaborate…
like the total dimension of wire when turn 5 times…or the wire dimension
of single wire?
Akki Sankpal says
or just tell the wires diameter in gauge.. that will more help to every1
Akki Sankpal says
can we use the copper wire used in old radio?
Swagatam says
it should be around 0.8mm thick (in diameter)
Z Curtis says
Can you make a wireless system using an old cordless phone setup?
Swagatam says
as a wireless speaker or something else??
Anonymous says
Sir I made this Transmitter and tested this at 3 V as you said . It worked but higher frequencies were distorted . Then I centered tapped the coil now I could hear faint music with lot of distortion . What might be wrong ??
Swagatam says
I think it will require 9V and not 3V as given in the article, pls try it with 9V supply.
Anonymous says
Sir I checked centered tapping at 9 V only . Now I corrected the issue by rewinding the coil but still higher frequencies are distorted . What to do ??
bell says
hello. can 50 meter range be extend to 100 or 150 meter?
bell says
hello. sir could 50 meter range be extend to 100 or 150 meter? what could be done?
Swagatam says
No it cannot be done without many elaborate modifications. You may refer to the following article for a possible solution.
https://homemade-circuits.com/2014/08/spy-bug-circuits.html
E.sabarinathan. M.eaganathan says
Hai great friend .I am sabari.I am dng it as a CLG science club competition.
Doubt is how the out put from eat wire should be connected on c1&ground help me sir.
Tomorrow I want to finish
Swagatam says
Hi, you can apply any music input such as from the headphone socket of cellphone or TV, DVD player ipod or from any music gadget headphone socket
E.sabarinathan. M.eaganathan says
Thank u fr this project I a got first prize finally.but not 100% good output I got…
I am doing again for tomorrow competition..
This time output is not coming..😟time is too short.I want to show tomorrow..
Plese clarify some doubts sir
1)say capacitor code for (3.3pf&10pf) I can't get correct component from shop😶
2)I am using 9 v battery.is c7 is necessory
3)can I use breadboard wire as inductor(after removing the plastic enamol)
4)say radious of winding &gap between winding
5)can u send image of coil using here.I want to see sir please my mail is (mail2sabariksr@gmail.com)😍
6)please contact with me on mail great friend
Thank you for spending our time for me🙌
Swagatam says
thanks sabari and congrats on your success.
3.3pF and 10pF does not require any code…you'll have to tell the shopkeeper as it's given
if you are using a battery then C7 might not be required…however a 9V PP3 batt will drain out quickly because the current consumption of this circuit can be pretty high.
the coil dimensions can be seen in the following example article,,,see the first image
https://homemade-circuits.com/2011/12/how-to-make-fm-remote-control-using-fm.html
you can see image here:
http://4.bp.blogspot.com/-UvYzmnSC_es/TusVkUH5pCI/AAAAAAAAAVI/MnHKf669lPw/s1600/Spy+Bug.jpg
the coil should be made from super enamel copper wires, other forms of wires will not do..
Soumen Bhowmik says
sir, I don't have 10pf I have two 4.7pf can I use ? if yes how??? thanks…. good night
Swagatam says
connect them in parallel
Soumen Bhowmik says
And sir can I use 2k7 in the place of 2k2…..thanks
Swagatam says
yes will do
Soumen Bhowmik says
I must make some mistake that's why it's not working…….. bye the way thanks for your valuable time sir…..
Soumen Bhowmik says
oh yes!!!! I tested it in a room it's working… sound is not clear…. I think inductor is the reason…..
Swagatam says
OK, great, adjust the volume correctly and use a long antenna, high volume input or small antenna can affect the performance…
preferably use a 9V battery or if you are using a AC/DC power supply make sure to use a large filter capacitor across the supply terminals
you can try a mobile charger adapter as the power supply
Soumen Bhowmik says
sir my radio is catching regular FM stations mine…..but I don't know what is my frequency because my station is playing every where and I got some points where it became loud…….. in that points I can get a good sound hiz hiz sound……sir can u say me how to stop the nose…… thank you very much….
Swagatam says
Soumen, take your radio to some distance, may be 10, 20 meters away from the transmitter, and tweak to locate the station which produces the most optimal and clean response.
you can also try your mobile FM for the same but from a closer distance to the transmitter
Soumen Bhowmik says
finally I found my mistake…. there was a connection problem at C3…..now there is no noise ….I got a really good sound…… I got success…… it is the result of your help and my curiosity….. this is my first circuit…. I never built any circuit before because I don't have a vast idea on circuit….. I am just a 12th pass student……you are the boss…. love you sir…
Swagatam says
congrats Soumen!! that's indeed a great achievement, because RF circuits are never easy, especially for the newcomers.
I wish you all the best….and do keep posting your feedbacks.
Preston Jose says
Sir, Can i use a 9v DC power supply instead of the transformer, 4 diodes and the capacitor?
Swagatam says
Jose, what kind of power supply are you referring to? is it an SMPS type? then it will do.
Santanu Dey says
Dear Swagatam,
Can I use 0.914 mm dia super enameled wire in place of 1mm dia?
Could you suggest me ant good websites to buy electronics components online?
Please reply as soon as possible.
Regards,
Santanu Dey
Swag says
Hi Santanu, you can use 0.9mm wire, slight difference in the diameter will not affect the results. there are many online electronic part stores like digikey, mouser, onsemi, elemnt14 etc all are good.
Carl Gustafson says
I built a pond and waterfall and have it lighted for the nighttime but I cannot hear it. I would like to build a circuit that would pick up the sound and transmit it to a speaker wirelessly. Is that possible? Could I use two Arduinos for input and output and would it sound like anything beyond noise. Thanks.
Swag says
If you want to pick the exact sound of water fall and send it wirelessly to another nearby location, the above circuit can do it without an Arduino.
Simply install the above circuit near the waterfall, and tune an FM radio receiver near you, to pickup the amplified the sound beside you.