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Have you ever wanted to broadcast your own radio station within your neighborhood? Ever get curious on where people get those "Surveillance Bugs" from spy and action movies? This small and simple FM transmitter is the toy that geeks have always wanted.

FM transmitters can be complicated to build, that's why I'm teaching you how to make a foolproof FM transmitter. There's no need to buy kits, this tutorial includes the PCB layout and the schematics. It has a range of up to 1/4 mile or more. It's great for room monitoring, baby listening and nature research.

My Experience:

FM transmitters remind me of my early years in electronics. When I was 8, I came across Art Swan's FM transmitter circuit. At the time I had no idea of where I'm supposed to buy the parts, so I recycled mine out of junk. I guess the biggest struggle that you're going to face is finding a trimmer capacitor. I'll give some tips on the last step of this instructable. In a nutshell, I highly recommend this project for everyone and also those who are still new in electronics.

>>>>>>>WARNING: You may experience nostalgia! :D<<<<<<<

Technical Specifications:

- 1/4 Mile Radius Range

-Powered By A 9V Battery

- Lasts For Several Days

- Adjustable 87-108MHz

Please Watch: Celebrating the 1st episode of my new YouTube channel! It's my first time to document a project with videography. I hope you guys enjoy the vid! Please leave a comment below, I would appreciate some advise regarding the video.

Disclaimer: This project is for educational purposes only and is not intended to air/ interfere with present radio channels. Neither site nor I, am liable for careless actions. Please check for the legality before attempting the project within your area. As long as

Step 1: Gather The Parts

All of these are available on any branch of RadioShack! :)

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MISC:

- Copper Clad PCB/ Perfboard

- Solid Gauge # 18 Wire

- Electret Microphone

- ¼" Bolt

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Transistors:

- 2N3904 General NPN Transistor (2x)

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Capacitors:

- 15pF or 40pF Trimmer Capacitor

- 100nF Ceramic Capacitor (2x)

- 10nF Ceramic Capacitor

- 4pF Ceramic Capacitor

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Resistors:

- 1M Ohm ¼w Resistor

- 100K Ohm ¼w Resistor

- 10K Ohm ¼w Resistor (3x)

- 1K Ohm ¼w Resistor

- 100 Ohm ¼w Resistor

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Tools:

- A Pair Of Pliers

- Soldering Iron

- Hot Glue Gun

Step 2: PCB & Schematics

I designed a compact PCB layout for Art Swan's miniature FM transmitter circuit using Fritzing. Use this step as your reference for the assembly.

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About The Circuit: These is the exact description of Art Swan, the circuit's Author, "This miniature transmitter is easy to construct and can be picked up on any standard FM receiver. It has a range of up to 1/4 mile or more. It's great for room monitoring, baby listening and nature research"

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Download Link:https://docs.google.com/file/d/0BwP5mrDBOvNYaHFnME...

Step 3: Print The PCB Layout

Download the PDF file then print it with your printer's standard setting then cut the printed layout. Be careful when cutting, the tip of my thumb got sliced by the sharp cutter blade.

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Download Link: https://drive.google.com/file/d/0BwP5mrDBOvNYaHFn...

Step 4: Develop The PCB

I'm using something what's called presensitized PCB fabrication, it's different from the toner transfer method. If you're not familiar with presensitized PCBs, better go with the toner transfer method.

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Presensitized PCBs: I expose mine directly to a 10W fluorescent lamp for 5:20 minutes then use a dilute solution of Sodium Hydroxide to develop the exposed PCB.

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Here's a separate tutorial for the PCB fabrication:

Step 5: Etch The PCB

Pour Ferric Chloride on a plastic tray then start to etch the PCB.

Step 6: Clean The PCB

Use a swab and Acetone to remove the photo-positive layer/ toner.

Step 7: Solder The Components

Use step #2 as your reference. Solder the smaller parts first. Start with the resistors, the capacitors, the transistors, the coil, the antenna then the 9V cattery clip.

Step 8: Construct The Coil

Strip a solid gauge #18 wire. Use a 1/4" bolt then turn the wire 7-8 times.

Step 9: Adding The Antenna

Solder a hook-up wire to the antenna pin, it's located on the 2nd transistor's collector pin. Use a maximum of 8 inches an a minimum of 5 inches.

Step 10: Recycle A Battery Clip

The key to this compact transmitter is the ingenious battery clip.You can get one by dismantling an scrap 9v battery.

Step 11: Glue Them Together

Apply a generous blob of hot glue to hold the clip and the transmitter circuit together.

Step 12: Breadboard Version

Recently, people have been asking me if it's possible to make this project without having to fabricate a PCB. The answer is yes. In fact I built my first FM transmitter on a perfboard. I guess some are new to this, no worries I'm here to teach you.

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The answer to this is a "Perfboard/ Prototype board. It's a PCB designed for prototyping circuits. There are three types of perfboards, the one that suits our needs is the dot matrix version. If you're new to this, make magazine has handy YouTube tutorial.

Step 13: Tune The Transmitter

Turn on your radio then tune it to your desired channel frequency. You'll get more range from the vacant channels. Don't touch the coil, just turn the trimmer capacitor until you hear a feedback from the radio.

Step 14: Q&A - Tips & Tricks

Where Can I Buy The Parts?

If you live in the US, all the parts that I've used are available from Radioshack. You don't believe me? The parts from my first non-recycled transmitter came from RadioShack, Long Island, NY branch.

Any Alternatives For The Trimmer Capacitor?

Most likely, you'll find one from a scrap transistor radios however you can replace it with a 20pF ceramic capacitor then rely on the coil's adjustment for compensation. Trimmer caps are color coded, only use the Red, Green or Yellow. I used the yellow since it covers a wider range.

Which Wire Should I Use?

Only use solid wires that has a thickness of 18 - 22 gauge. When I was still a novice hobbyist, I was worried about the strict selection of parts. Don't worry too much, eventually you'll learn to improvise when parts are not available.

Why Does The Frequency Change After Tuning?

Let's admit it, tuning the radio is a bloody challenge! If you use a metal screw driver to tune the trimmer cap, chances are you'll end up having a different frequency broadcast the moment you lift the screw driver. This is why non conductive screw drivers are recommended.

Where Can I Find A Non-Conductive Screwdriver?

You'll easily find one from a PC repair shop, or maybe form a hardware store. If you really can't find one, the famous Little Bits kit comes with it.

Is It Possible To Connect A 3.5mm Audio Jack?

Yes, it's possible! All you need to do is to link the common ground then solder a 1K ohm resistor each channel (L & R) forming a junction. Now solder a wire from the junction to U1's collector pin (refer to the schematic). You can now connect your MP3 player! I'll post an additional step regarding this mod.

Can I Hook This On A 12v Car Battery?

This project would still operate at voltages between 7v-14v, so yeah it's compatible. If you want to stay safe and prevent the circuit from burning, solder a 10 ohm resistor in series with the FM transmitter and 12v battery.

Is This Legal?

As long as you don't use it to spy on others and not use a long & huge antenna then yes, it's legal. Just don't use it near an airport. For more info, pleas read the FCC Rules.

Step 15: Don't Forget To Leave A Comment [Stay Tuned]

Please don't forget leave a comment below. Thank you!

Schedule:

2nd Week - DIY Pocket Spudgun

3rd Week - Homebrew Continuous Tazer

4th Week - Crystal Radio

5th Week - Solar Car (School Investigatory Project)

<p>If your transmitter does not work - and you verified that all connections are OK - then it may be that the oscillator does not oscillate (I've found it the hard way). Desolder your antenna and try again at close distance. I've used the (advised elsewhere) quarter-wave flexible wire antenna and my oscillator worked only at super high frequencies. At lower ones it was damped down - see attached images.</p>
Can copper 22 # gauge wire be used instead?
I want to know insteaded of 100nf and 10nf capacitor we can use 100uf and 10uf capacitor and how to calculate frequency in therotical
<p>any body tell me </p><p>how can i set the frequency on our fm radio</p>
<p>set your fm radio to the lowest band... try 88.9</p>
<p>Is there a reason your questions get posted so many times ?</p>
<p>can i use smartphone's radio to read frequency from fm transmitter.</p>
<p>yes I tried it.</p>
<p>Hi I made your instructable... I used a mono socket for my microphone. I'm planing to use it as a wireless mic. I also replaced the 4 pf with 5 pf because it's unavailable and used 22 swg 9 turns instead what you did in your instructable. Nice work ;)</p><p>...Anyway how can I improved the signal without touching the microphone? The reception improves clearly when I curl the wire of the microphone with my hand. </p>
<p>I couldn't buy trimmer capacitors because I couldn't find in store(here is only one store where you can buy Electronic components)and I have other trimmer capacitors with different capacity and will this work if I will use it?</p>
<p>any body tell me </p><p>how can i set the frequency on our fm radio</p>
<p>go through the video first <br>at the last you can see that he(the tech guy) adjusts the screw on the top to get get the desired frequency<br>first you need to set the frequency through you wanna hear in the receiver<br>then adjust the screw until you can hear clearly<br></p><p>let me know if it works </p>
<p>any body tell me </p><p>how can i set the frequency on our fm radio</p>
<p>any body tell me </p><p>how can i set the frequency on our fm radio</p>
<p>any body tell me </p><p>how can i set the frequency on our fm radio</p>
<p>but not work</p>
<p>but not work</p>
<p>Hi, so I made this on a breadboard and it works. My radio can pick up my voice (and a lot of noise). <br><br>But the main problem I'm not sure how to solve is that I have to be talking directly into the tiny electret microphone in order for it to work. <br>Even if I'm 2 inch away, it won't work.<br><br>How do I solve this problem? <br><br>Is this a problem because I am using a breadboard? I don't think that would affect how sensitive it is to my voice? But I expect that it contributes to the background noise.</p>
<p>wow.. trying to build it in breadboard.. but cant find the output frequency.. can u tell about your inductor.. what wire and how many turns.. if you can reply with your circuit image it will be so helpful for me.. Thank You .. </p>
<p>same problem here</p><p>it is not working</p><p>7 turns of copper wire for inductor</p>
<p>same problem here</p><p>it is not working</p><p>7 turns of copper wire for inductor</p>
<p>same problem here</p><p>it is not working</p><p>7 turns of copper wire for inductor</p>
<p>same problem here</p><p>it is not working</p><p>7 turns of copper wire for inductor</p>
<p>do you maybe have a schismatic of how you did it on breadboard. mine does not seem to work </p>
<p>My transmitter is broadcasting on 17 MHz range i think its the inductor, could i just buy a .1 uH inductor component instead of making a coil?</p>
<p>i do it but not working in any way</p><p>can you help me</p>
<p>my project dose not working any way</p><p>please any body help me as soon as posible</p>
<p>Hello,</p><p>Could I use a 2n2222 instead of the 2N3904?</p><p>Thanks</p>
<p>can you please attach corel draw x4 cdr file of pcb layout</p><p>please reply as soon as possible .</p>
<p>Hey everyone</p><p>I'd love to rebuild this project , but I did not find the right parts. Would it be possible that someone publish a link collection.</p>
Thanks for this nice posting.
pcb layout size in printer machine plz
<p>dimention of pcb </p>
<p>aprox 350 x 150 mm</p>
<p>Hi. Thanks for this instructable, I haven't tried this for a long time! Though it seems like I have some problem with the soldering, I need to review it ;)</p>
Thanks dude. Works great.
Pcb layout size of print what?
Sorry, I'm not sure what your question is exactly.
<p>is it possible to connect a LASER as the input to the transmitter and then decode the signal at the receiver so as to make a wireless counter?</p>
<p>I made it and it works. But when the voice is loud signal is losing and starts to buzzing. When i whisper to the mic i can hear my voice from radio clearly. Every quiet sounds become louder even tick tocks of wall clock.</p>
<p>Can you maybe show the other side. my arrangement is the same, but i don't get a transmission.</p><p>Thanks</p>

About This Instructable

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Bio: Hi I'm Angelo! I am a 17 y/o Physics Major at the DLSU and I use my course as an inspiration for making ... More »
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