loading

In this instructable I'm going to show you how to build your own portable audio transmitter. This transmits FM waves so you could easily get the signals on your mobile phone, radios, etc. As the name and the picture indicates it is very small and is approximately the size of a 9v battery clip.

This transmitter is like the ones in the movies which are used to spy on people or try to record conversations, well don't use this this to spy on anyone, its just for educational purpose only.

What does this do?

  • Well all this is a FM transmitter so you could start your own mini FM station.

I'm going to build a mini FM receiver soon, to go with the mini FM transmitter

How does this work?

Well all of us have heard of "frequency modulation", most commonly known as "FM", this circuit works on the very same principal to transmit audio signals captured by the microphone. This circuit uses BC547 transistor to amplify the signal and then frequency modulate it. Since it is tiny and powered with just 9v the signal range is limited to only 15m.

If you like my project you can vote for me in the battery powered contest.

OK now enough of the talking and let's start building.

Step 1: Tools and Components

Like always lets start with getting all the parts, the list is quite simple all you need is

Components

Tools

<p>AWESOME! I've built dozens of FM transmitters but never have I seen one that's soldered on top of a 9v clip. Your project made me build another one :)</p><p>_________________________</p><p>BTW, try the two-stage 'Super Spy Bug&quot;. I think you'll get more gain and rage out of it. Here's a schematic :)</p>
<p>Thanks ASCAS</p><p>Any idea on how much range you got from it. Currently I'm working on a similar FM receiver and I may make 'Super Spy Bug&quot; once that's done. Then you would get a complete spy set.</p>
Please can I have the circuit diagram of this mini Audio Transmitter? Thanks this is my email Gospelustas@yahoo.Com. Thanks for the Love
<p>The original author of the circuit said that it can transmit FM signals up to a quarter mile (depending on your antenna). We ran a test on the football field from my previous school. We received a clear signal across it, about 120 meters. I guess it can still cover a wider range, although I still haven't tested at lengths beyond 120m. </p>
<p>can i use on this fm transmitter bc547b becase i can't find 2n3904 transistor ?</p>
<p>Just made one but with direct audio input, now I'll try to make a microphone for it.</p>
<p>Very good! I like this one :)</p>
<p>I'm very interested on radio commutations. Your circuit looks really neat and simple. Double vote for you.</p>
<p>Thanks <a href="https://www.instructables.com/member/Victor8o5/" rel="nofollow" style="">Victor8o5</a></p>
<p>I meant to say communications, damn autocorrect... </p><p>Again, thanks for your instructable.</p>
<p>Hey! I'm new here! I would like to make this kind of transmitter but I'm afraid that it will not work properly! Is there any tips on how exactly I should to do every step? I need to know that because the soldering, the position of any of this components including the battery (I don't know why) the turns of the inductor, all this have matter and depending on this all facts the transmitter will work! It is not like battery and the light bulb, which position you want to join them they will still work! I don't know I confuse myself! I had made the circuit given by ASCAS but it didn't work properly! I need help on this! What about your circuit how you solder all the components together? With cables or something else? </p>
how i online bay electronic Components?<br>plz give me any website link because i want to bay electronic components .<br>thanx<br>
this is a very nice n awesome project I am going to make it..<br>I have two question...<br>1). is transmitting FM signal is legal in india?<br>2). and how I attach a 3.5 mm headphone jack on it instead of microphone...<br>thanks in advance n keep posting instructables like it.....:-)
<p>1. Unless you are using it block specific radio stations, you will be okay. Small, low-power radio transmitters are almost always legal in most countries.</p>
<p>how to make the inductor?and what is its inductance?</p>
First thanks for the great 'ible.<br>So i bought one of those cheap fm transmitters for cars and i wanted to hook up a normal mic, the kind with 3.5mm jack, to it. So that i can broadcast my voice to an FM frequency in short range. The transmitter has an AUX, USB and micro SD slot. Any ideas?
It's not working plz help me
Please show the circuit
<p>How to connect the wire antenna ?<br></p>
how can i build it ..i want ckt. diagram of it
<p>whats the pin congif of variable capacitor , help needed</p>
Give me the circuit diagram...
@Thisissteve, that was awesome, I want to build something the same for the purpose of acquiring practical skills, Please can I have the circuit diagram? Thanks
<p>Ha ha, finally got this right. And it's so useful to jam the neighbor loud radio played at night.</p><p>All i need to do is plug it in and tune till the right frequency where the neighbor radio become silence.... Peace ! </p>
<p>hahaha.. very nice ;-)</p>
<p>can mic be replaced with music instrument jack? </p>
<p>nice and simple</p>
<p>Nice work</p>
hi Steve, I make it, I have used 56pf ceramic disc capacitor instead of 47pf variable. but it is hard to find frequency. and I want to know can I use bc557 or bc548 instead of bc547. and 10kpf capacitor instead of 1n. and how to increase the transmitter's range.
What would be the Farad:Hertz ratio for the trimmer cap?
<p>how do I hook up a mic to the audio input of a tune-free audio fm transmitter</p>
Great I can use this to spy on my husband.
can i use a variable tune capacitor use in selecting radio channels instead of trimmer capacitors
<p>why microphone used in it</p>
Nice project but I have tried may times to make one but I have failed to make it transmit
how many gauge wire should I use for the coil ?
oh yeah I made it<br><br><br>I have one question <br><br>where did you get this circuit digram from? <br><br>I want to show this as my project so I will be needing all information about it <br><br>please share the information how it works ?
<p>one more thing ..the shopkeeper always give me a POT when ever i ask for trimmer capacitor...is it ok if i use POT</p>
<p>By 'pot' I assume you mean potentiometer, right? A potentiometer is actually a variable resistor, not a variable capacitor, and it will not work. </p>
Hey Steve, What's the range of this transmitter.
<p>ho can i connect my phone on the transmitter ,and is the transmitter stereo?</p>
<p>i have built mini audio transmitter as per ur circuit diagram.i am very sure that there are no touchings in the circuit. my project guide also checked it .the circuit is working but the voltage at the base of transistor should vary when music is playing in front of microphone then only it means it is detecting signal . but it is not varying. we checked connections also, but we didn't find any mistake. please can u help me ? .my project submission is on 30th march. i am sending pics of circuit i have connected.</p>
<p>what wire is used for inductor? and i have a variable capacitor .it has10/60 on it. can i use it .please reply me quickly. i have less time to do my mini project.</p>
Hey, really good proejct!<br>but I have one more question: Do i have to use the transistor of the transcription, or does qork every kind of trabaistor?
*transistor:-)<br>
<p>HI! I'm making this mini transmitter but i have a problem with trimmer(variable capacitor)connections.I don't know exactly which terminals are to be connected to the coil.Please help.</p>
<p>awsm........</p>
<p>awsm........</p>
plz tell me can i use bc557 i found bc547 as pnp
plz help me...where can I find trimmer

About This Instructable

171,619views

1,188favorites

License:

Bio: Hey I'm a College school student, I love to work on projects and Arduino powers most of them. Follow me @ https://www.facebook.com ...
More by ThisIsSteve:Linkit One Text to Speech Linkit One Kitchen Timer Intel Edison Talks to Linkit One 
Add instructable to: