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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>The schematic diagram included a 0.01pF Capacitor - which is not existent anywhere (unless probably its a DIY capacitor). This capacitor isn't included on the parts list so i guess its a mistake</p>
<p>Search for 10 nF</p>
<p>0.01pF is not equal to 10nF... i'm guessing that 10nf (equals 0.01 microFarad) is in place for the 0.01pF.... - its probably a typo error</p>
<p>Probably so. I didn't see it anywhere either.</p>
<p>Works fine but I got 1 Problem: The Microphone is really silent...i got to turn my mobile on full volume to get decent volume in the radio...is there a way to amplify the mic more?</p>
Thanks dude. Works great.
<p>its working or not</p>
<p>It worked fine. I couldn't specify a transmit frequency, but I could pick up the signal on a few open channels.</p>
<p>im already done make the circuit but im still cannot get the frequency that i want..can u look my circuit if have mistake..tq</p>
<p>I found that getting a specified frequency given the author's proposed hardware setup is quite difficult. I end up getting whatever frequency is not broadcasting very strongly in my area. Just try scanning through all AM and FM frequencies and turning up the gain on your transmitter.</p>
Would u sent me a breadboard circuit degin photo?
Pcb layout size of print what?
Sorry, I'm not sure what your question is exactly.
<p>how if i use the value trimmer capacitor 120pF..can or not?</p>
<p>Hi, i tried to make it with exact component but still not getting any output. Any help?</p>
<p>can i operate it at 5 volts? I want to revise it design and make it run with USB power.</p>
<p>If you remove the resistors in the correct places and place a wire there instead, you might be able to run it on a lower voltage.</p>
<p>where does the middle pin of the capacitor go?</p>
I think that it should go in the transistor<br>
I am not able to get 4pf ceramic capacitor. Can i replace it with any other component?
<p>I was just wondering how would you increase the range of this?</p>
<p>its probably the antenna. if you want a very long range but in one direction make a yagi. if you want just more better range in all directions (not as good for range as a yagi but better then a piece of wire) make a dipole. you could also make a rf amp but the battery life would suffer and it would be bigger (also you would need to modify the PCB design)</p>
<p>This transmitter is literally impossible to tune without a non-conductive screwdriver. It really should be a part of the list of required tools!</p>
hello friend i have a confusion in assembling the 3.5mm audio jack in place of mic can u please explain or send a pic to me
<p>I would think that you could just do the trade 'straight across'. The positive would go to the positive, negative to negative. Or did you try that and get no result?</p>
<p>SomeTImes i get the output and sometimes Wont. <br>What Could be the problem . Any solution to this .<br>Any One Can Help me out with This ?</p>
I tried making this the other day and something went horribly wrong. I tried following both your actual photos and schematic, but still ended up with about three components out of place. do you think you could share a color coded drawing of the board with what components go into which holes? Because I think the problem I'm having is that I opted to use a pre-drilled prototyping board rather than etch one for the first run. So now I've got to de-solder all my components and try again.
Hi, I am looking to make a radio transmitter for a larger project for school and I was wondering if it was possible to play a sound pattern continually, for example a beep?<br><br>Thanks
Amazing instructable! I remember reading about these bugs in one of the eveil genius books and they were small enough to fit in a soda cap running off of a 3V button cell battery. Is there any way to adapt this circuit to also work on 3V instead of 9V? Shrinking it down is what interests me as im planing on using 0603 SMD components for it.
<p>Yes! Very easily, just attach 3 of the 3V button cells in series, like so:</p><p>+V1- +V2- +V3-</p><p>The positive face of V1 becomes the positive face of the battery while the negative face of V3 becomes the negative face of the battery. A decent way to attach the batteries might be to just press them together firmly and hot glue the seam, but not the faces. That way the faces can continue the circuit while the highly resistive glue holds the faces together. This would have the added bonus of tripling the battery life of the transmitter.</p>
Can copper 22 # gauge wire be used instead?
<p>yes . you can</p>
I'm quite confused. In your video it says 20pf or 40pf trimmer cap, but in your written instructions 8t says 15pf or 40pf trimmer cap. Please kindly explain.. :)
Can i use any capacitor without using 4pF ceramic capacitor?? Pls answer.
<p>i was woundering how would you change the frequency to be able to use more than one in a small space ?</p>
How to find the capacitance of trimmer capacitor and how to find the certine frequency?
<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>yeah posible</p><p>but u need modulated signal </p>
<p>how can i know in which freqency the transmitter transmitting</p>
<p>it doesnt work ,, may be problem with inductance</p>
Can i use 1/2 watt resistors instead of 1/4?
Yes. You can use even 1/8 watt resistors ;)
<p>Hello,</p><p>Could I use a 2n2222 instead of the 2N3904?</p><p>Thanks</p>
<p>probably. if you do try it could you let me know how it turns our as i don&quot;t have any 3904s either</p>
<p>any body tell me </p><p>how can i set the frequency on our fm radio</p>
<p>Adjust your 15pF or 40pF Trimmer Capacitor</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>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>
I want to know insteaded of 100nf and 10nf capacitor we can use 100uf and 10uf capacitor and how to calculate frequency in therotical

About This Instructable

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Bio: Hi I'm Angelo! I am a 18 y/o college sophomore taking my majors in BS-ECE at the DLSU. I use my course as ... More »
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