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Hi everyone,this is the best device I had ever made in my life I think because it is useful for my daily use.I had an old FM radio which was of no use catching dust in the cupboard.So,I thought of making an FM transmitter because that radio had no input port and I need to buy a new set of speakers.This was the perfect and cheapest solution of the problem.You can transmit sound in the range of about 250 meters.CLARITY WILL BE HIGHEST ON YOUR FM RADIO(NOT SMARTPHONE RADIO FUNCTION) AND EVEN IT WILL EXTEND THE RANGE TO 320-350 METERS.The schematic is from the website www.makezine.com. In my transmitter the frequency was between 97.8-98.8

Features :-

  1. Long battery life
  2. Long range
  3. Wearable
  4. Connect to your smartphone
  5. Crystal clear sound on FM radio
  6. Compatible to any device with 3.5 mm jack output
  7. Cheapest 0.6 $
  8. Easy setup with easily available parts

Here's a video of it working :-

Step 1: Parts Required

For this project you will need :-

  1. 2 X 10 pf capacitor (ceramic with written "10" on it)
  2. 2N3904 transistor
  3. Mono audio pin 3.5 mm
  4. 10 uf electrolytic capacitor (minimum 16 v)
  5. 2 X 0.01 uf ceramic capacitor (written 103 on it)
  6. 3.5 mm pin socket (optional)
  7. 18-22 gauge solid copper wire
  8. Perf board
  9. 9 volt battery
  10. 10 kilo ohm resistor
  11. 27 kilo ohm resistor
  12. 470 ohm resistor
  13. Some wires
  14. Solder
  15. 9 volt battery connector

Tools :-

  1. Nipper
  2. Soldering iron
  3. A pair of scissors
  4. Hot glue gun

Step 2: Perf Board and Schematics

Circuits assembled on pref board are not necessarily fragile but may be less impact-resistant than printed circuit boards.Here's a schematic of the FM transmitter.Place the components correctly as displayed in the schematic.Capacitor (10 uf) has polarity so keep in mind the terminals of the capacitor negative is for audio pin and the positive is joined to resistor.You may face some problems while doing it on pref board. Firstly place all components with some space between them.If you are a beginner then the space between components should be more.It would prevent risk of shot circuit.While placing the transistor keep in mind the pin out of 2N3904 transistor.Place all components and then solder them carefully and cut off the extra pins using a nipper.

Step 3: Making the Coil

Take a 1/4 inch bolt and wrap around a 18 - 22 gauge wire carefully.Make about 4-5 turns and then unscrew it form the bolt and cut off extra wire.It is preferred to have stripped wire instead of insulated one.And your coil is ready!

Step 4: Connecting Wires to 3.5 Mm Plug

Open the cap take two wires and solder both of them to pins of plug.The smaller pin wire would be connected to negative side of electrolytic capacitor and the other to ground.After soldering screw down the cap ,Choose the length of wires according to your choice.

Step 5: Perf Board Soldering

Solder the audio plug to corresponding places.Now solder all the ground pins of the components together.Make sure that the ground connections should not touch positive pins of components.In the picture the black wires are all the ground connections.At last solder the 9 volt battery connector to board remembering the correct place for both terminals.

Step 6: Checking

After soldering everything ,insert the plug in your phone that have FM radio.Play any easily recognizable track and on the other side connect the 9 volt battery to connector.Connect earphones to other mobile phone or use any FM radio and search for track changing frequency on radio and when you find the clearest sound stop there.That's the right frequency on which the transmitter sends signals.Mine was 98.4 Mhz. Sometimes between 97.8-98.8 Mhz.To increase range add two antennas to the circuit but make sure that the two antennas don't make contact with each other.

Step 7: Making Enclosure

Use Duct tape,cardboard and some other tools to make a box for transmitter. Leave some space for switch,wires of audio plug and I prefer to leave the top open.

Step 8: Rest Place for Audio Plug!

Take 3.5 mm headphone jack port and join it to the same side where audio plug comes out.You need not to connect the port pins anywhere it is just a rest place for plug to make the device more handy and portable preventing mess of wires.I had increased the length of audio plug and also had twisted both wires to make them more compact.

Step 9: Making Strap

Make the strap out of any material which suits you,I had used elastic material so that it can fit everyone's hand making it usable for everyone.To see how to make this see my another instructable Caretaker's Gear v2.0 (more portable).

Step 10: Done!

This is a real working project which would not only reduce normal expenses but also gives education about working of radio transmission.It is a perfect device for people who love radio communication.It prevents usage of loud speaker in our home to play music in each and every room.Hence, reducing noise pollution.Queries and improvements are most welcome you can ask me by commenting!

Please vote if you like!

Good bye!

Make and enjoy!

Thanks!

actually I can't get reach to a 103 capacitor but I have lots of 104 cap now please guide me what to do next. Thank you
OK I got similar cap of 103 and it is written as 0.001AEC will it be okay?
<p>If you want to see the conversion for Caps., see my web page of USA vs EURO</p><p>http://elecurls.tripod.com/ Also see my: Calculator page.</p>
Yes!yes! Correct it is same!! Sorry for my earlier comment. Best of luck for your project!! :-)
<p>I think it is 102!! Try if you can find out 103 in old telephone PCBs or T.V !!!!</p>
<p>there is a lot of difference between 10nf and 100nf.I would suggest you to look for 103 capacitor as this device is having less adaptability!! Thank you for showing interest in project!! :-)</p>
<p>Can we use polyester capacitor instead of ceramic ?</p>
<p>can any wire work in place 18-22 gauge wire?</p><p>any wire ?</p>
<p>can any wire work in place 18-22 gauge wire?</p><p>any wire ?</p>
<p>Not Enough Power.<br>I have finally made one of this but had to change the 18 gague wire by a 16 gague because i could not find the 18 gague at my local store, but when I connect the transmitter to the Battery I need to put my radio's antenna over it in order to get any sound at max volume.<br><br>Frequency is between 85.5 and 90 MHZ with 4 Turns of wire of the Coil. And I need to set volume to MAX in order to hear something, I also listen a lot of Static too.</p><p>Does any one have any recommendation? </p><p>Sorry for my bad english.</p>
<p>What are the Wattage's of the resistors?</p>
<p>It seems to be 1/4 watt</p>
<p>Absolutely right! 1/4 watt.We can judge it from it size and shape!! Thank you friend! :-)</p>
<p>Welcome friend</p>
Hi my friend it's a verry good and smart transmitter i made it but i was looking for a reciver for it simple as the transmitter ^_^ so i hope u have one
I was trying to modifying it to make it transfer video signals when it's ready I. will share it <br>but do you think it's gonna work !!!! ^_
<p>If you do hard work ! You would surely achieve success ! You can try internet radio!:-) Thank you!</p>
<p>Nicely built ,I will make in this November! Keep up the good work!</p>
Why did you make it so HUGE ? You could easily have made it 1/4 of that size. It looks like you deliberately made it stupidly big.
<p>I t will make every beginner for soldering an easy task! I too agree with you!This could be made pretty small using small rechargeable battery.Using copper clad board!Thank you for your comment!</p>
<p>Hello my friend,could u post a link exactly this transmitter's schematic?</p>
<p>You can check the step pictures! Thank you ! :-)</p>
<p>I am a bit concerned here...<br>The circuit might be working fine for transmitting a signal but it also acts as a source of massive interference.<br>There is no metal enclosure preventing this and the oversized designed causes even more unwanted signals to be produced.<br>In most countries it it also an offence to transmit with such power levels in the commecial FM bands.</p><p>And being held together by sticky tape I highly doubt it will survive real action for more than a few hours.<br>And IMHO putting something like this on a wrist does not make it wearable....</p>
<p>I too agree with you but here I don't make a pirate radio station.It was just for fun and I can reduce the range too check out the comments.I tried to make one with microphone but I failed to make it! Thank you for commenting!:-)</p>
<p>Where can i buy a piece of wire for coil?</p><p>Thanks</p>
<p>Buy it from any fan repairing shop,choose any wire between 18-22 awg.Best of luck!!</p><p>Thanks!</p>
where is reciver
<p>I think you are asking about the receiver in the video that is the other mobile phone in my hand and if in this ible,receiver is yet to be made in this november!Thanks for showing interest! :-)</p>
Nice work bro
<p>Thank you! :-)</p>
<p>It works!!</p><p>I used 2N2222 transistor instead 2N3904, all components are reused from an old radio. I'm actually surprised that it worked at all, because of old components and my dirty style of building. </p><p>The working frequency is quite wide, it covers range between 108 and 106 MHz. The bass is quite strong and you have to search right frequency a little, to find a more appealing sound. After success with first one, I decided to build another one. Now all I need is some box.</p>
<p>Glad to know this! Nicely built! Keep up this good work</p>
how can I change my frequency
<p>You can use a trimmer capacitors!! Change its value and the frequency will change. :)</p>
<p>Great idea!! :-) </p><p>Thank you!!</p>
<p>Try replacing 10 uf polarized capacitor with any capacitor between 1-33uf and it will affect the frequency or change number of turns in the coil. Thanks!!!!Best of luck for your project :-)</p>
Does anyone know of i can add a potentiometer to change the frequency? Great project still
<p>Thank you! Just give a try for trimmer resistor but I think trimmer capacitor will work!!</p><p>Best of luck for your project! :-)</p>
question on voltage. Am I right in thinking that this would handle up to the 14v you get in a car as long as the electrolytic capacitor and transistor were rated high enough for that voltage? Values on any components wouldn't need to change?
<p>I don't know exactly but it is better to be safe use only 9v battery as I am sure about it that it won;t harm!! Thanx for showing interest!Thank you friend! :-)</p>
<p>Cheers. Easy enough to reduce voltage to it, just be nice not to have to.</p>
<p>Do you have any ideea how to connect it directly to a microphone? (computer microphone if possible)</p>
<p>Check out some schematics for making a pre amp for condenser microphone! Best of luck for your project!! Thank you friend! :-)</p>
<p>Good job !</p><p>KEEP A GOING !!!</p>
<p>Thank you friend! :-)</p>
Cool project man :)
<p>Thank you friend! :-)</p>
<p>You need to explain a bit more clearly what you are doing as it isn't immediately obvious. So you take an audio source, transmit using an FM frequency to an &quot;unused&quot; FM channel. Where I live (UK), the communications folk would take a dim view of this, possibly an unlicenced transmitter and the neighbours might not be too keen either, but good luck. Needs a bit more work on the production model.</p>
<p>I just checked on Amazon UK, you can buy a lot of devices that do the same time...maybe not as powerful though http://www.amazon.co.uk/s/ref=nb_sb_noss?url=search-alias%3Daps&amp;field-keywords=fm+transmitter</p>
<p>Thank you friend ! </p>

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