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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)

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>
<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>do you maybe have a schismatic of how you did it on breadboard. mine does not seem to work </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>Does anyone have the layout for adding a 3.2 jack port. I.ll like to add the jack instead of the mic. </p><p>Thanks</p>
What are the calculations for this circuit if you wish to make changes to it?
i made it and it works.my mobile's fm doesnot recives this,but a radio set gives a crystal clear sound upto 100m<br>i did not used the trimmer cap,as it was unavailable,so i used a 12pf cap and did some calculations for the inductor turns, to set the frequency at 100Mhz.so when i turned it on the frequency was suprisingly really close to100Mhz.and by the way i built it on a copper clad... so thanx for the circuit and good luck to all<br>
<p>Hi, how did you make those calculations? And, how many turns did you make to the wire for getting 100MHz?</p>
<p>hello, can i use a audio socket or jack at the place of mic, so that it would not require two transistor, please suggest. i dont want to use mic</p>
<p>I made it with a 22pf capacitor (not trimmer),with a copper coil of 8 turns. It does not have much range and it doesnt give even a little clear reception. Any help?</p>
<p>If I dont want to use the trimmer capacitor, any alternative? </p>
<p>Wont the frequency change as battery power deteriorates? Anyway to fix that, such as voltage regulartor?? </p>
This is my complete and not working project.
<p>I can't be certain from your photo of the underside but you may very well have some unintentional solder bridges. Have you checked for this?</p>
I have checked it and fixed many times so it looks that ugly. This was one of my first experiences with soldering so I think that I have burned some components. But after month of troubleshooting I have decided to build a new one from talkingelectronics.com. I did much better solder work but it still doesn't work wery well. Microphone has extremely low sensitivity. I know that electret microphone is not very sensitive, but that circuit has 2 transistors so it has to be sensitive.
<p>hi everyone i try to make it. but i could not find 4pf ceramic disc capacitor. there is only 4.7pf caps. can i use it instead? will it do?</p>
<p>hi everyone i try to make it. but i could not find 4pf ceramic disk capacitor. there is only 4.7pf caps. my question is will it do? thank you before any suggestion given.</p>
<p>i made it and it works, then i decided to do it smaller, like on turtorial. Now it doesn't work correctly. I can tune it on 90 MHz, and can hear tap on antena, battery, resistors contacts.. etc, but i can't hear sound from mic =( If don't to touch anything, I can not hear even the noise. Also I cant hear feedback. </p><p>Probably someone have same problem or have a solution? </p>
<p>I accidentally bought a 3 pin trimmer capacitor, can I use it anyway in this configuration? if yes how?</p><p>Also it would be nice to have a 3.5mm jack audio output, Is it tricky to replace the mic with it?</p>
Two pins are + and -, and the third one is output on trimmer . Check on Google which one is which. And I think that you can connect 3,5mm jack. But I'm not sure how...
<p>Film capacitors are okay, no? Would I need to adjust the components if I use those?</p><p>I made one with the ceramic and it gives really noisy feedback even in quite a distance.</p><p>Why is that?</p>
<p>So I now have the problem that I can't seem to make a decent coil with good dimensions, so I wanted to ask if I can just buy an inductance like these (german site, but most of the data is easy to read):</p><p><a href="https://goo.gl/klZA2E" rel="nofollow">https://goo.gl/klZA2E</a></p><p><a href="https://goo.gl/jMpo97" rel="nofollow">https://goo.gl/jMpo97</a></p><p>The picture showing the circuit stated 0.1 &micro;H for the coil, so I just looked up for that value, and all results save for those 2 resistor-like ones are SMD sized.</p>
<p>could you do a tutorial on how to make it without the board?</p>
<p>I can't seem to find any 4pF capacitors in my country (germany), will a 3.3pF or a 4.7pF capacitor work too?</p><p>Also is the given value for the trimmer capacitors the high value, the low value or is it somewhere in the middle of the range?</p>
<p>I used a 5pF Capasitor and it works fine</p><p>I think it is the high value but if you buy the yellow one I think it will be fine</p>
<p>Thank you for the project I really enjoyed making it</p><p>It works great!</p>
Can I modify it that it will transmit on 446 mhz?
I made it all ready but it doesn't work. I have ORANGE trimmer capacitor. It can turn infinitely, is it broken?
I forgot to say that it transmits on fm.
I made this circuit. but I am unable to receive the signals on FM but I am receiving the signals on AM . how is this possible
<p>Most probably its the inductor u made... <br>frequency, f=1/(2Pi*sqrt(LC)) so, if the inductor is a little over 0.1uH, it makes huge difference...</p>
<p>cant say works like a charm, but it works. But the broadcast is too noisy and also very short range...<br>need some work on those... </p>
<p>I made it but somehow i cant seem to tune it. Did i do anything wrong here?</p>
<p>How long is your antenna?</p>
<p>7 inches</p>
<p>Try to replace your antenna to a longer, about 30 inches.</p>
<p>i added a long antenna on it, Even with the fm radio next to it it still doesnt pick up anything. The coil is made from silverplated copper, i assume that would work?</p>
<p>Can You measure the voltage across the base-emitter voltage of the transistor located at the coil?</p>
<p>unfortunatly i dont have a multimeter here,</p><p>all i can provide is that emitter =5.5v base =6.2 collector = 5.5v.the coil itself has 7,5 volts running through it.</p><p>I apologize if the tings i say dont make alot of sence, im a hobbyist in electronics only.</p>
<p>If voltage at the base is 6.2v, i think the transistor is broken.</p><p>(Standard base-emitter voltage is 0.7v)</p>

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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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