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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

______________________________

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>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>
<p>I have same problem with ryuk3 ,,</p><p>result for measure voltage tr located at the coil ,, 0,6V ?</p><p>but not function ? what need must be check how about michrophone how to check that?</p>
<p>I have replaced the transistor with a new one. I still get the same voltages though.</p>
<p>Now I do not know what you can do with it, or you can try replacing the coil with a 6 turns.</p>
<p>thanks a lot though for giving your input, much appriciated!</p><p>ill try making a new one if i have time.</p>
<p>I have replaced the transistor with a new one. I still get the same voltages though.</p>
<p>I made it but it doesnt work ,Can you help me find out the problem </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>I'm sad about your finger i hope you got well :/</p>
<p>Hi, can I replace the 2N3904 General NPN Transistor by a BC547B? ThankYou!</p>
<p>Yes</p>
<p>hay can i use 3.3pf or 5pf ceramic capacitors then 4pf.</p>
<p>You can use 5pF capacitor</p>
<p>same problem, cant find 4 pf in my countrie</p>
I made it, but its not working. Plz anybody help me.
<p>If you have BC547 transistors, reverse collector and emitter.</p>
<p>check your transistors.....I think there direction is opposite</p>
<p>He means you need to measure the inductance of the coil.</p>
you need one or more electronic device to check it
Sorry I can't understand which electronic devices ?<br>
you need to one device which <br>View the unity measures the power of Henry
you need to one device which <br>View the unity measures the power of Henry
<p>Where can I find the pieces?</p>
<p>i need a project report on this Device......is anyone could help than mail me at</p><p>mtzaroon@live.com</p>
I made it but it not any one can make it work this work for the person who have been studying that but if you mke it all what you think you can reach to make it working ,i love it and I will made example that coming soon ,thanks for all
<p>you try put a 8volt battery???</p>
9v i'm now studying that subject
sorry , project*
<p>Estupendo proyecto de electr&oacute;nica , que permite desarrollar la creatividad de nuestros j&oacute;venes investigadores al tiempo que su en prendimiento va tomando forma sin sospechar sus resultados.</p>
<p>great project</p><p>can i place your project on my website.</p><p>i'm working on a website which is related to electrical projects.</p><p>i also mention your name.</p><p>plz reply</p>
<p>Where can i get the mic? Plz reply.</p>
from any telephone or from phone shop
Hello! I just want to ask? where did you bought your 40pF Trim Cap? Is it in Deeco? And how much is it? Thanks! I hope you can read this as soon as you can :) - bonn, Makati
I built it in a breadboard but it is not working I can't get signal to my mobile gm radio software <br>I'm attaching the photograph of the circuit<br>please check whether I'm doing anything wrong
This is also something to keep in mind for most audio circuits, doing them on a breadboard is never going to be very successful because distance and grounding become very criticle aspects when boosting a small signal to a bigger signal
<p>Wil not work on a breadboard, it's FM</p>
<p>In the forum post linked below, one reply suggests that it's a bad idea to try to build an FM transmitter on a breadboard: &quot;The wires on the breadboard will act as antenas and pick up stray RF, in additon to the capacitance between each strip messing with the calibration of the circuit.&quot;</p><p> <a href="http://www.electro-tech-online.com/threads/understanding-fm-transmitter-circuit.105702/" rel="nofollow">http://www.electro-tech-online.com/threads/underst...</a></p>
<p>16,000 Step By Step Woodworking Plans http://yaz.ma/nui3i</p>
<p>Hi All .. I want to build a FM transmitter to transmit to more than 1 frequency at the same time.. Is this in any way possible ? Tx Mairus </p>
<p>I misread the range, I thought it it said 14 miles not a 1/4of a mile. But still it's genius!</p>
<p>how long will the battery last?</p>
<p>Cool stuff you got there.</p>
<p>Cool</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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