FM transmitters can be complicated to build, but not this one — this iPod FM transmitter about the easiest you can possibly make. And though the science of radio is well understood, there’s a magical, emotional quality about it that we don’t often stop to appreciate. You will not forget the first time you pick up a transmission broadcast from a device you soldered together, yourself, from a few bits of copper, carbon, plastic, and wire.

I am indebted to Jim and Kat of Sonodrome for first introducing me to that experience, through this very circuit, which I first built on a pre-etched PCB from a kit they offered for sale as recently as 2011.

This design was originally popularized by Japanese multimedia artist Tetsuo Kogawa. The circuit itself is a slight variation on Kogawa’s simplest FM transmitter design, and the method of building it is sometimes referred to as “Manhattan style.” It uses a piece of copper-clad circuit board but, rather than etching the circuit traces through the copper layer, a large piece of continuously-plated board is used to make all the circuit’s ground connections, and small sections of plated board are glued to the surface to form nodes or “pads” that are insulated from ground.  Besides being a convenient way to assemble circuits using minimal tools, this building method encourages you to think about circuits in an interesting way — as groups of connections that are either grounded or “floating above” ground.

kogawa_simplest_transmitter

This transmitter uses ten on-board components and will transmit a monaural audio signal about 30 feet. It is possible to extend that range by adding an antenna, and Mr. Kogawa’s website has more information about how to do that.

title_001

NOTE: Depending on where you live, operating an FM transmitter — even a very short-range one like this — may be illegal without a license. Unless you attach an antenna, it’s very unlikely that anyone will notice or complain about any transmissions you may make with this device. On the other hand, it’s very difficult to predict, before construction is complete, just where on the FM band this transmitter will broadcast. Use due caution during testing, and make sure you understand the law in your area before attaching the battery.

Steps

Step #1: Form the coil.

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  • Strip about 4" of 18AWG solid copper wire and wind 4 turns around the threads of a 1/4-20 bolt.
  • Turn the coiled wire off the bolt as if you're unthreading a nut, and clip each lead to about 1cm.
  • Bend little "feet" on the ends of the leads and adjust them so the coil will stand upright.
  • Holding a pair of pliers in each hand, grab the coil's leads and stretch it evenly along its length until the feet are 12mm apart on center. You may need to even out the coil spacing with a screwdriver or other tool.

Step #2: Cut the board.

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  • Use a straightedge, a utility knife, and the edge of a table to score and snap a 5cm × 4cm rectangle from the copper-clad board. This will be your ground plane.
  • Score and snap a 5mm × 5cm strip of copper-clad board, then score it crosswise at 5mm increments. Snap along these lines, with pliers, to create several 5mm × 5mm "pads." You only need 5, but you may want to make a couple extra.
  • Smooth the corners and edges of the ground plane and the pads with a small file. Be especially careful to remove any sharp copper burrs that might cause cuts on handling.

Step #3: Mount the coil.

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  • Apply a small drop of cyanoacrylate glue to the underside of one of the pads. It doesn't take much. Use tweezers or small pliers to carefully position it in the center of the ground plane. Wait a few seconds for the glue to set.
  • Glue a second pad to the board, above and to the left of the first, along a line running at about 135° with respect to the long centerline of the board, as shown. Position the second pad along this line so that there's about 12mm between the centers of the first and second pads. Wait a few seconds for the glue to set.
  • Solder the coil across the 2 pads as shown. This will be easiest if you pre-tin the surface of each pad, and both coil feet, before applying heat to reflow the solder and join the tinned areas.

Step #4: Add capacitor C3 and resistor R2.

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  • Solder a 0.01μF ceramic disk capacitor (C3) between pad 2 and the ground plane, and trim away any excess leads. It doesn't especially matter where you connect to the ground plane, for this or any other connection in the project.
  • Glue pad 3 to the board somewhere below and to the left of pad 2, as shown. You want enough space between pads 2 and 3 to fit the body of a 1/4W resistor.
  • Solder a 1/4W 27K resistor (R2) between pads 2 and 3, as shown. Trim any excess leads.

Step #5: Add the electrolytic cap, resistor R1, and capacitor C2.

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  • Glue pad 4 to the ground plane just to the left of pad 3. Space the pads to match the lead spacing on your electrolytic capacitor. Solder the electrolytic cap (C1) between pads 3 and 4, making sure the negative (–) lead is connected to pad 4.
  • Solder a 10K resistor (R1) between pad 3 and ground.
  • Solder a 0.01μF ceramic disk capacitor (C2) in parallel to the 10K resistor between pad 3 and ground.

Step #6: Add the transistor.

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  • Bend the transistor's 3 leads, as shown.
  • Glue pad 5 to the board directly to the right of pad 1. Make sure it's close enough to pad 1 that one of your transistor's leads can reach between them.
  • Solder your transistor across pads 1, 3, and 5, as shown. The collector connects to pad 1, the base to pad 3, and the emitter to pad 5. Trim any excess leads.

Step #7: Add the 10pF caps, resistor R3, and the battery clip.

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  • Solder one 10pF ceramic disk cap (C5) across the transistor's collector and emitter, (i.e. between pads 1 and 5), and a second 10pF ceramic disk cap (C4) between pad 1 and the ground plane. Trim any excess leads.
  • NOTE: For more convenient adjustment of the transmitting frequency, replace the 10pF capacitor (C4) between pad 1 and ground with a 20pF variable or "trim" cap. If you use a variable cap, the frequency can be adjusted simply by turning the trimmer shaft with a small screwdriver.
  • Solder a 470Ω resistor between pad 5 and the ground plane. Trim any excess leads.
  • Connect a 9V battery clip to the board, as shown, by soldering the red lead to pad 2 and the black lead to the ground plane.

Step #8: Attach the phone plug.

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  • Unscrew the threaded housing from the tip-shield (TS) mono phone plug and set it aside. Solder a 4" length of red stranded wire to the center "tip" contact, and a 4" length of black stranded wire to the outer "shield" contact.
  • The shield contact has built-in prongs that can be crimped over onto the wires to provide strain relief for the solder connections. Use small pliers to fold these prongs over and crimp the wires beneath them, being careful not to crimp so hard you damage the wire insulation, bend the tip contact onto the shield contact, or otherwise short the 2 connections.
  • Slip the threaded housing over the wires and tighten it onto the plug threads again. Solder the free end of the red wire to pad 4, and the free end of the black wire to the ground plane.

Step #9: Tune it up!

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  • Attach your 9V battery to the battery clip and insert the phone plug into an audio source like an MP3 player or smartphone. Start a song or other easily-recognizable audio track playing, then turn on your radio and scan through the FM band to locate the transmission.
  • TIPS:
    • Start with your receiver right next to the transmitter.
    • A digital tuner with precision down to 0.01MHz may be helpful.
    • Be patient and careful. Scanning is a bit tedious, but if you get impatient you may miss the signal altogether and mistakenly believe the transmitter isn't working.
    • If you scan the entire band and can't locate your signal, try changing the orientation of your receiver's antenna with respect to the board and scanning again.
    • It's best to run your audio source on battery power when you are first isolating the transmitting frequency. If you have to run it from mains power, make sure electrically noisy devices like fluorescent lights, TVs, and computer monitors are not active on the same circuit at the time.
  • You can tune the transmitting frequency by changing the spacing between turns in the coil. Closing the spacing will lower the transmitting frequency, while opening it up will raise the transmitting frequency. You can also use a variable capacitor for tuning (see Step 7).

Step #10: Mount the battery.

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  • NOTE: This transmitter design needs very clean, smooth power, which is one of the reasons we choose to run it from a battery. Power from a "wall wart" or other AC adapter is smooth enough for most DC applications, but not for this radio transmitter. Using an AC adapter to power this transmitter is likely to cause the signal to be too noisy to use.
  • Use scissors to cut a strip of hook-and-loop fastener (velcro) tape to fit the length of your 9V battery.
  • Separate the hook and loop sides of the tape, remove the backing from each, and apply the hook (scratchy) side to the bottom of the transmitter board. Apply the loop (fuzzy) side to one of the battery's 2 largest faces.
  • Attach the transmitter to the battery using the velcro during use. When depleted, the battery can be removed and separated from the transmitter for recharging.
Sean Michael Ragan

Sean Michael Ragan

I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and makezine.com. My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.


  • chuck

    Cool circuit. This has a lot of potential for serious fun.
    Throw a silent rave- with a small transmitter and antenna you can broadcast music to your party. Have your guests bring headphone radios and have a silent dance floor. Bonus points for broadcasting different music styles on different frequencies- it looks super cool to have folks dancing at different speeds and styles.
    Do a pirate drive-in. Use a digital projector and a laptop to show a movie on a conveniently placed wall in an empty parking lot. Broadcast the audio over the radio transmitter, invite your friends and re-live the glory days of drive-in theaters.
    Create walking tours and locational radio art. Build several transmitters on the same frequency. Set them in an area or along a path. Use the individual transmitters to broadcast parts of a story tied to the location, describe sites along a walking tour or broadcast a location specific ‘soundtrack’ to your park or campus. As the listener moves along the path or area they pick up the transmitters in succession. Set up a spatially connected choose-your-own adventure story in your neighborhood where route choices affect the story being broadcast. Depending on how far apart you space them you can get glitchy signal overlaps and noisy resonance and things.
    The FCC doesn’t really care about small hobby circuits like this as long as there are no complaints. With less people listening to radio or watching broadcast television, there’s little chance of causing interference that will lead to complaints. Don’t be rude or stupid, avoid large or weird antennas and don’t try to be the next Radio Caroline and everything will be cool.

  • http://zero-waste.co.uk Roy Shearer

    I made a PCB version of this transmitter and made laser cut housings for it – check out http://www.openthing.org/products/niftymitter/

    Have used them regularly for art installations and within the house as a wireless speaker system, great fun!

  • David

    the law is the same every where, because it is a Federal Law, that says what you can use to broadcast, and that you must be licensed to send voice over the air, would expect that data would fall under the same category. This from first hand knowledge, I built an FM (may be was AM back in the day, think this was before FM) I sold it to a friend and he set up his own neighborhood radio station, and before he knew it the FCC was knocking on his door….lol

    • willnonya

      You assume everyone is in the US.

  • ibrahim

    I want to know how a FM transmitter works. Where can I find information on that.

    • http://gravatar.com/teirisias teiresias

      If you happen to see a necropost: the bookstore at ARRL.org is a good place to start.

  • http://ne-zaman.net Ne-zaman

    very good

  • http://www.medyumaslan.com medyum

    thanks for sharing. good video!

  • Ral

    I found some good information on the FCC website concerning low power radio transmission. It looks like that from standpoint of the FCC that this device would fall into the “Part 15 Devices” category and not require a license.

    http://www.fcc.gov/guides/low-power-broadcast-radio-stations

    I would assume that the FM transmitters that you buy in the store to play audio from a media player through your car radio (for cars that do not have an AUX input) would also fall into this category.

  • ahoule

    how do you set the frequency

    • TerryT

      The frequency depends on the inductance of the coil and the value of the 10pf capacitors. The easiest way to adjust the frequency, for example to move away from a strong local broadcaster, is to slightly squeeze or stretch the coil.

  • S_Hennig

    Thanks for reviving some memories. Decades ago I built lot’s of prototypes that way. The only thing I did differently: I used a Dremel to make isolated pads instead of glueing bits of PCB. That way I did not have to wait for the glue to set. Cheap and easy and works up to VHF (well, obviously ;-)

  • stinker

    i better want to know how this circuit is working…

  • stub

    On a stereo jack, the tip of the jack carries the right channel and the ring of the jack carries the left channel. Would it be better to use a stereo plug (tip/ring/sleeve) and solder the tip and ring together in the plug, rather than allowing the mono plug to connect the left channel to ground in the mp3 player’s jack?

  • Shawn

    Great tutorial, but I think you should include HOW the circuit works as well. It would be nice to see the explanation behind the design of the project.

    • AJ

      Agreed :)

  • http://canonprinter99x.blogspot.com ria

    its cheap and easy to build circuit, i will try it.

  • deojo

    Can i remove audio jack, and replace it with electret microphone

    • stub

      I haven’t seen ANY replies from the author here. So I thought I’d chime in. I think an electret mic requires some power. Also the mic signal will be weak and might require some (pre) amplification. But I may be wrong about that.

      • Elmo

        We have tried to put an electret microphone, but the sound quality is not good, but you will hear a significant sound coming out of the receiver .

        • deojo

          please share your result here, if you get way to fix it. :D

  • Levi

    I put this together and for some reason I still can’t find it on the radio and my 9v seems to get hot pretty fast. Any advice would be great thanks!!

    • John

      I imagine that you have shorted the battery’s red and black lead somehow. Use an ohm meter or continuity checker between the terminals of the battery plug (with the battery unplugged). You should see a very high resistance value or an open. If not then check your wiring. Watch for solder shots from the pads to the ground plane.

  • John

    Why use a mono plug? I understand that the transmitter will only transmit monophonically, but with a mono plug you will only transmit one channel from the MP3 player (left or right but not both) loosing part of the music. The better choice is to use a stereo plug and run the red wire to both the left and right pins (black wire to ground as shown). Then you get both channels transmitted!

  • scott

    i built the transmitter as well, how does the amount of turns on the coil affect the signal ….is more better or less

  • AJ

    I’ve built three of them and none of them worked. I triple checked everything and I connected everything correctly. I did use double-sided copper as that was all radioshack had. Is that OK? Troubleshooting?

    • AJ

      When I touch one end of the coil I can sometimes get a clear signal to 107.3. Please help.

      • Pvt. Parts

        Yes I had this but on the transistor E leg, Turs out C2 ground leg did not get solderd well… I did get signals in 89.7 and 99.9 but it is not clear at all :(

  • Pvt. Parts

    Any suggestions on how to make it more clear on sound? when just voice is getting transmitted no problem, but when the music comes in it sounds like a chainsaw

    • Keen

      lessen the volume of the input audio signal to get a more clear sound.

  • Aditya Vardhan

    Where Should I Install The Antennae please tell me

  • aadil

    what+is+the+value+of+the+electrolytic+capacitor.and+also+tell+me+values+of+all+componants.

    • stub

      You can look up the RadioShack parts and get the values from there.

  • http://idonthaveawebsite.com JT

    Built on breadboard. Not functional.
    How is carrier wave produced?

    Thx

    • stub

      Seemed like the copper ground plate was pretty specific. Do you think your breadboard is functioning the same way (ground-plate-wise)?

      • Vish

        I want to connect this transmitter to the tv rca output and i tried it but its not working plz help me…..
        Thanx

  • Dwayne

    You should try making an IC type transmitter.

  • Tibi

    I build a lot of these transmitters when I was a kid. Had a lot of fun playing with it baut it sucks that they’re so sensible to changes in temperature and mechanical shock. Every time you touch it or even get close to it, it changes frequency and you have to tune in to find the broadcast. Having a crystal in the equation makes it stable but those circuits are a lot more complicated to build.

  • http://twitter.com/charsh92 Harsh Chandola (@charsh92)

    can an Inductor of predefined value of certain inductance be used instead of the coil? I couldn’t find an 18 gauge solid copper wire but I have a 1mm diameter copper wire, will that work?
    If an inductor can be placed instead of a coil what value must it have?
    Thank You

  • http://willnonya.wordpress.com willnonya

    The text suggest that an AC power source would be too noisy for this, what would you think about using an automotive 12v dc source or USB to power this?

  • vish

    I want to connect this transmitter to the tv rca output and i tried it but its not working plz help me…..

  • Todd

    Could this design be adapted to broadcast in stereo?

  • Andrzej

    I have question to you. How can I connect antena to this circut. Thanks.
    P.S awesome project

  • Toad of Toad Hall

    Very interesting. Quite illegal, of course.
    But, oh dear, didn’t they teach you to look after your tools?

  • nusak

    i would like to interested so much !! how can we use the mic test the sound ??

  • Christian Juth

    Can I use a 0.01 uF mylar capacitor? I know the charge and discharge are slower but will it work? The voltage rating is above the 9v that the circuit can provide so it should be fine. But will the slower discharge matter?

  • lim

    could you can show all details for the resistor ! Cuz i final year wan to do it

  • EchaaBoy Shehroz

    transistor value ?

  • Jake

    It has been very hard for me to find solid copper in my area can I use tinned copper instead?

    • Nathanael Beall

      use a standard cable wire, (for TV installation) there usually 18 awg

  • http://www.pinterest.com/onceuponamine/ AplAceY0uc@nCaLLh0mE

    Is it possible to make it any smaller?

    • Gareth Andrews

      size? yes. components? not really.

      • http://www.pinterest.com/onceuponamine/ AplAceY0uc@nCaLLh0mE

        shame

  • WH

    This is fantastic. Thank you very much for posting it. It works very well. I use it in the car in order to connect my phone to the radio so i can play whatever i want. Without antenna the range is just 1 or 2 meters so it doesn’t cause any interference at all. When i attached an 82cm long copper wire as an antenna the range went up to 100m or so. I may connect the circuit to the 12V electrical circuit of the car. I assume it will just increase the range.

    • Thilina Jayasingha

      Is it works realy.i’m not make it. But i wanto know what freaquency can heard you?plz reply me as soon as possible.

      • WH

        yes, it works but the frequency is sensitive. In prototype board i
        first got 91MHz then i built the circuit on copper board and the freq
        went down to 86MHz which is out of the FM range. In my experience the frequency also depends on the battery level and whether or not an antenna (that can be an 80cm long copper wire) is connected to the output. I checked the output freq with a high freq oscilloscope.
        If you use a 2-22pF variable capacitor in place of C5 you can change the output freq. The less the capacitance the higher the output frequency but the less the output performance will be. You can compensate the performance drop by adding an antenna but it affects the freq a little.

  • Koby

    this is awesome I’m going to make one. But where would you connect the antenna?

    • Zidane Tribal

      you would hook up the antenna to the emitter of the transistor. at least thats what the diagram shows and how i have it hooked up. havent tested the distance yet.

  • noahstewart

    Has anyone created a stereo version of this?

    • Shrivardhan Kantharia

      yes i have but it’s not working

  • Zidane Tribal

    i made this myself, but it seems that with a 9v battery i can only use volume 36 at most without significant distortion. i dont know much about transistors and their voltage ratings, but i hooked it up using 18 volts and it was running fine and i could use a higher input voltage as well. hoever, after about an hour the 2 9v batteries were warm – how would i check the current draw? i tried the amp probe on my meter but it didnt work.

    • -FireControlman 2nd Class USN

      current draw would be P/E. power divided by voltage, so you have to do the math and find the current through the collector and go from there

  • Amitabh Songara

    sir
    can you tell how we can change the frequency

  • Phương Đăng Trần Thành

    How can i change the frequency by changing the coil because in my country, trimcap is not available

    • michael george

      you can change the coil by using a variable coil or changing the number of turns or length or diameter of your old coil

  • Seth Nintendo

    How many watts?

    • -FireControlman 2nd Class USN

      P=IE

  • Finnley

    I could not get mine to work do you have any suggestions

    • davidson

      can we see yours?

  • Saurabh Singh

    is any substitution of 2N3904 transistor.If exists pls reply.

    • Gareth Andrews

      2N3904 / BC547 / PN2222 / 2N4401 are all NPN transistors,

      don’t know if they’ll work but its worth a try :)

  • concerned_legal_citizen

    Sean, I just finished building the fm transmitter. I did get it to work, however, it is very sensitive touching any of the components on the board. I added a 3 inch antenna. To get the transmitter to work, I have to adjust the coil and then back away about 6 feet to hear it working. Is the one you built this sensitive to frequency changes and proximity to your body?

  • Declan Embury

    would it be possible to connect i mic directly into the transmitter?

    • -FireControlman 2nd Class USN

      yes absolutely, it will take the same input audio frequencies that you apply with your voice the same as it would music from a phone.
      -FireControlman 2nd Class USN

  • -FireControlman 2nd Class USN

    I love this stuff, although im having trouble breaking down the signal flow, and description of each component and how they are ‘reacting’ to each other.

  • sajjad

    Hi, I have build this circuit, but it does not work
    is there anybody to help me with that?
    if yes, I will send the picture of the circuit that I have build it on the bread board.
    To tell you the truth, I dont know even it works, or not? (I mean maybe I have the wrong frequency to be catch with FM)

    • sajjad

      I found the mistake
      there was an error in my transistor. I simply plugged it reverse on the bread board. ;)))
      when it worked, it’s frequency was about 91 KHz
      Thanks for your great & simple project

  • saisrikar

    should the enamel of copper wire be removed?

    • Gareth Andrews

      only where you are going to solder

  • C4rb0N

    I can use this capacitor ->http://goo.gl/xONSf1 instead of C1? Please help..

    • Gareth Andrews

      give it a try, the voltage can be higher that’s ‘okay’, but the uF most probably will change the frequency, you will have to tinker with the coil if you use the 33uF cap

  • vibtechs

    Great post..!!!!
    I like this Post. It is so nice to read such wonderful blog. Thanks for sharing!

    Regard
    Ganpati Engineering

  • Abdallah Osman

    by replacing the audiojack with a microphone, will i need to an additional component to transmit my voice? thank you

    • Gareth Andrews

      “yes absolutely, it will take the same input audio frequencies that you apply with your voice the same as it would music from a phone.”
      -FireControlman 2nd Class USN

      all ready answered :P

  • Vishnu Suresh

    can i use it with out Copper-clad board, about 5cm × 5cm .i can’t get that in my locality .is there any way to use it without that……..

    • Gareth Andrews

      YES you can!, as long as the circuit connection are the same it’ll work, what you talking about is a “rat’s nest circuit”, i do this allot as i too cant get copper clad where i stay

  • Vishnu Suresh

    can i use it with out Copper-clad board, about 5cm × 5cm .i can’t get that in my locality .is there any way to use it without that……..

  • caswell

    Hi, I have built the super simple radio transmitter, it works but the signal is too noisy or scratchy, what can I do to enhance, I suspect my coil is the problem as it is not even, it is also found too low in the FM spectrum, how can I move it up to the mix be range of the spectrum, thanks a lot, enjoyed building it……caswell

  • dqsdsq

    doesnt work…wow…I tried everything… :c

    • michael george

      1-Try to use a very long antenna such as : a dish of aluminum from the kitchen :D :) I’m not joking, I connected my antenna to a very big dish and it works.

      2- check your connections, I’m sure you will find something wrong.

      3- check your power supply ( battery or transformer ).

      4- use another coil and capacitor ( L1 and C5 ) and it’s better to use variable capacitor and coil so that you can change the frequency and your radio may receive the new frequency. I think the old frequency is out of the range of your radio.

  • Vishnu Suresh

    can i use it with out Copper-clad board, about 5cm × 5cm .i can’t get that in my locality .is there any way to use it without that……..

  • michael george

    This is an amazing circuit. it works properly :)
    but it would be better if you explained the function of each component in details.
    Would you tell me what the function of C4 is ?
    Thanks in advance sir,

  • JP

    Can I substitute the 18 gauge coper wire for something else because its hard to find where I live?

  • Annesha Roy

    can anyone tell me the all parts name and specification…

  • Anup Upadhyaya

    Where can I find the hardware used ? Can I find it inside a CD player? Or inside a Radio ?
    P.S. : I am not a electronics student.

  • Irfanuddin Shafi

    Hey,
    I couldn’t get 500v 0.01uF Capacitors, i got smaller(size) one of it(same value i.e, 0.01uF), stating AEC is it Okay? :O

    • jonas Biensack

      jup, the 500V doesn’t matter, even a 16V will work

      • Irfanuddin Shafi

        Thank you for your sincere reply. I’ve got another question, I have built the circuit, it works. But there’s a lot of noise and frequency changes often. Also, the sound is not clear.

        • jonas Biensack

          How did you build it? Can you provide a picture of your work?

          kind regards Jonas

          • Irfanuddin Shafi

            I had built it on copper clad board.
            Here’s the pictures

          • jonas Biensack

            Not so bad at all, but why don’t use a smaller pcb like mentioned avove (5cm*5cm). And your soldering points are looking extremly bad (cold ones), make them new and test again.

          • Irfanuddin Shafi

            Can you give me your email? I will contact through that.

      • ghggygh

        at what frequency it transmits signal???????

  • Dhave Gatchalian

    can i use bc548 transistor?

  • Clark

    Will an aluminium foil covered board make any difference in performance when compared to copper clad board?

    • ASPACEMAN

      Good question, anyone? I tried to get the pieces to connect to a scrap piece of copper pipe, but I think that’s advanced soldering.

      Some DIY Copper board ideas!?

  • vaibhav

    can i use my mobilephone as receiver??……and can i connect condenser microphone at the input of the same circuit instead of audio device??

    • atar

      yes

  • Edwin Moses

    can i use bc 547 or bc107?

    • jonas Biensack

      yes

  • zubair

    can i make it on bread board??

  • John

    I made this on a breadboard witch did work, but it won’t transmitter like it did. I can barly hear the music and can’t find a set station for it. Could the transistor have broken or is it something else.

  • Aidan Payne

    Where would I attach an antenna that has multiple connections, like on taken from an old radio?

    • Irfanuddin Shafi

      One to capacitor c5 and the ground to ground plane.

  • santosh

    can i make this project on a pcb

    • Irfanuddin Shafi

      I’d suggest you to do it in Copper clad board.

  • Sam

    can i use a single sided copper clad board

    • Irfanuddin Shafi

      Yeah, the copper board acts as ground plane, and the pads are the ones that aren’t grounded.

  • brreszek .

    How many henr have inductor L1 ?

  • Irfanuddin Shafi

    I have built the circuit, it works. But there’s a lot of noise and frequency changes often. Also, the sound is not clear

  • Şhäšhwãţ Šïňğh

    Hello.. I have made one myself.. It doesn’t work at all… Any suggestions… I have used 30 kHz resistor in place of 27 kHz.. And my copper wire is thinner..

  • Arth shah

    Sir
    Here are some of the things which i wanted to ask u
    1.Can I use breadboard instead of copper clad board?
    2. Can I use a 33uf capacitor
    3. Will it work without any antenna?

  • Guest

    Hi! i’d like to use this transmitter in order to communicate with another device wireless (i want to control a simple robot with an arduino connected to my pc that makes this transmitter send some signals with a different duration and another arduino that receives the signal through a receiver)… is it possible? can someone help me to build the receiver that operates at those frequences?

  • marco girardini

    Hi! i’d like to use this FM transmitter in order to control a robot: i think I’ll control the transmitter through an arduino to send some different duration signal, so i could control all the motors just changing the duration of the signal. After that a receiver receives the signal and sends it to another arduino that controls the motors. Is it possible? can someone explain me how could i create a receiver that operates at the same frequences?

  • Sohit

    how can i run a toy car using these radio signals

  • Hans Peter

    Hey friends…I`m desperate cause sitting since one day and try to find the fault…i used a plugin panel to create it…but i cant find the frequency…is it possible to measure it with an oszilloscop?

  • Eric Melonakos

    Does the actual number of turns on the coil matter? And does the size of the turns matter? I don’t have a 1/4-20 bolt. Also, what does 1-33 uF for C1 mean? I have a bag of electrolytic capacitors, but they each just have a single value (e.g. 33 uF). Thanks for any help you can give!

    • Nick Vanderplop

      uF is the abbreviation for Pico-Ferads, where Ferad is a unit of how much power the capacitor can store, and pico means *10^-12, or in English, a decimal point with 12 zeros after it before the number. The person most likely meant by 1-33 uF that one with a capacitance anywhere between 1 and 33 uF ould work, or a pecial capacitor that is adjustable to accomadate more or less power.

      • ThisGuy…with2thumbs

        Newbie here…but, are you saying that choosing a capacitor between this range will vary the power output, and thereby increasing range of the signal?

        • Nick Vanderplop

          when i say “power” i am referring to the total power storage of the capacitor, not the output of the transmitter. What is made with the capacitor and the coil is knows as an oscillator, and a capacitor with higher capacitance charges slower (because it takes more power) and therefore lowers the frequency, and a capacitor with less capacitance charges quicker (because it takes less charge) and therefore makes the oscillator quicker. Neither directly affects the range.

          • ThisGuy…with2thumbs

            Ahh…I get it now…thank you. So, then, I could use a varicap for this capacitor to alter the frequency, right? With regard to output power, how does one increase the power output of a transmitter? My initial thought would be to increase the wattage being supplied through the power source, but then I start thinking about the components and their limits. How would you, say, double the power output of the transmitter in this example?

          • Nick Vanderplop

            simple: use a bigger transistor. That is the component that amplifies the power going to the antenna so it transmits more power than is going through the actual circuit itself. Strengthening that would strengthen your signal. Also, I strongly suggest an antenna (just a wire is fine) about 8 feet long. That makes the transmitter much more efficient.

          • ThisGuy…with2thumbs

            Hmm…that never crossed my mind! I’ll definitely try that! If I wanted to measure the power output, I’m assuming I would measure it from the emitter side, but how? Would I just measure once for amperage, and then a slightly different way for voltage, thereby getting power? All I have is a multimeter. To take a stab at it…measure voltage from emitter to ground, and amperage inline immediately following the connection to the emitter? Thanks again for answering these questions. I’ve recently become facinated with how radios work.

          • Nick Vanderplop

            to accurately measure the output of a radio you need special equipment as the power from the emitter to ground fluctuates as it transmits a signal. You could get very different readings based on what you are transmitting and how loud. That is one reason things like this exist:

          • ThisGuy…with2thumbs

            Alright…thank you tons for your advice!

  • Hemanth

    I am really happy that u posted this one . But is it possible to hook up a electret mic? Or antenna? If so where must I hook it up?? Pls reply as soon as possible because I want make this fm transmitter soon!!

  • Hemanth krishna

    can i add a electret microphone and a antenna?? If so where the broad? How to connect it? Pls reply and i am exited for this project

  • Utsav Naha

    If the transistor is pnp, will the postion of the tank L and C change?

  • Anil Yadav

    Not working at all,but found some disturbances at 94.1,Can i use a 5mH Inductor in place of coil.
    Tell me how to place the antenna

    33uF=??????

  • Prathamesh Belnekar

    any one can plse tell me where tu put the entinna

  • Naman Sachdeva

    I had a go a making it.
    From the initial component values, I was able to achieve oscillation around 136Mhz (as measured on my oscilloscope). The critical components that influence the frequency are the two 0.01uF (=10nF = 10,000pF = “103”pF) capacitors and the 4-turn (1/4 20 bolt former with #18 wire) inductor. While I used #16 wire, which will have influenced the inductance, I needed to alter these components in order to lower the resonant frequency of the carrier wave:
    I used larger 0.1uF = 100nF = 100,000pF = “104”pF capacitors and I used 6-turns of the inductor, spaced out to roughly 16mm or so (I failed to measure this width, so tweak it if needed). As they say, ” your mileage may vary”.

    With these larger oscillating components, the frequency was lowered to 99.65MHz as measured, and the results work well at 99.70MHz on the radio dial.

    The transmitter is ‘rough’, but can be made to sound clearly. I needed an antenna from the ground plane to radiate enough power to overcome a stronger commercial station at 99.7FM. Hand-capacitance was strong too, so you might need to listen with some correct body positioning near the circuit.

    Overall, a nice circuit as a demonstration, and with so few components, it offers a good learning tool to understand what is going on. However, I am still struggling to think through the processes and events in the circuit, so any comments on how this thing works are greatly appreciated!

  • raiden

    can u plzzz tell me the priciple on which it works….plzzz explian the working of the model ……it is for my physics project ……..plzz reply fast

  • Praneeth Mv

    I’ve not built this, but please can I know if i can connect a microphone/mic to it so that i can speak….?Thanks for any help.

  • MrJeppe

    If i want to add the antenna, where i should solder that?

    • Advait

      You would have to connect any piece of insulated wire to the emitter of the transistor. IF you connect that wire to a metal dish, then you will have some excellent range:)

  • Shaikh Nahal Maqsood

    What I I Want To Recive Signals From a Wire ? PleaseReply Me I Am Not The Student If of Engeering But Its My Project Please Reply Me ?

  • JS7457

    i make it and it so cool !! do it with a cooper board ! Very good quality for me !
    102,5 Mhz ! I use a 0.05mm solid cooper wire, 4 turns !

  • Mark Vincent Mendoza

    Sir Can anyone tell me if other earphone works too. Please please.

  • zazacd

    can i use BC108 NPN transistor

  • http://www.oakleysunglasses.co.com Oakley Sunglasses

    Turn the actual brim decrease and press it while using the iron.

  • Thom

    Can you make a part list of this FM transmitter on Conrad please? I don’t now exactly what the parts means.

  • Thom Debruin

    Can anyone make a parts list for me at Conrad or whatever.
    i don’t understand the parts and don’t now which one i should choose.
    please help me!!!

    • homerlaughlin

      From that question, You’ll put an eye out. Get a little transmitter on ebay and forget it.

  • saiteja

    Hi,
    i am saiteja doing undergratuate degree.i have built the fm transmitter and when i sent the audio signal,we are not getting the output i.e.., audio signal which we get at a certain frequency.so please give me suggestions to work out the project.

  • Alberto Sánchez

    Amazing project with great explanation, I am definitely trying it out! It is only missing a better explanation of how to add the antenna.

  • Peter

    hi there. i’m trying to understand the values of all the components, can you publish the derivations of the circuit

  • emily

    can u please explain what resistor r1 is and capacitor c2 are. in the materials they don’t tell us what those are can u baby the procedure steps to easier words

  • Jaso Salt

    Is it possible to add a microphone?

    • Connor Bunz

      Id imagine that you’d have to add some sort of amp to the mic, considering it probably doesn’t have any native power running through it

      • Nathanael Beall

        Thats what i had thought to, i think another npn tranistor might work like this

  • vishwanath k

    Sir ,
    Instead of copper clad board i have used normal PCB i am not getting output in my circuit also i have used C1 as 0.01uf has variable capacitor is not available in my region .PLEASE TELL ME HOW TO GET OUTPUT …
    thank you.

    • Eden Simpson

      Hi I recently made one of these, for C1 i used 1uf. the input doesn’t need to be very loud for it to work. For lack of copper board i used the 3D approach as seen in the picture.
      I used a BC547 as the transistor.

      My one is 96.1 mhz but it only works if you hold the Antenna.?

      • javier

        may be u have a bridge somewere, probably on ground, o you have not at all so you are instead when u touch it.

        • Advait

          I dont understand?
          how will that happen?

  • Colin55

    The 10p C4 should be 22p and it should be connected across the coil to form a tuned circuit or TANK CIRCUIT. You can make the 22p adjustable.
    For a full explanation of how each component works, see:
    http://www.talkingelectronics.com/projects/Spy%20Circuits/SpyCircuits-1.html

  • Jason Brambach

    This worked perfectly. Tuned in around 90.1. One thing to share: stick with the specified NPN transistor specified. I tried a pwn222a and it did not work at all. Thanks to Make and Sean for their great work. You share so many enriching projects.

    • Shrivardhan Kantharia

      i did but its not working. Can you tell me some tips or any precautions regarding construction of circuit

      • Advait

        Do not change any of the parts and it should be working nicely.

  • nikola bojkovski

    how can i make stereo transmitter ?

  • Joseph Irwin

    Interesting!

  • Stuart Canfield

    Hi, first off i want to thank Sean for this super simple circuit. Thank You :) At first i built this with a ball of wires, it was a bit chaotic, it tuned into 92fm with 10pf which was undesirable do to the fact it was on top of a station and didn’t come in good. I then put in a variable cap in place of it. This allowed me to get the full radio band with surprisingly good quality. After that i decided to take it a step further and designed a simple PCB board to put it on. I’m not sure if its because i mangled the wire a bit or the lack of Antenna, which i have made a spot for just haven’t tested it, But it does not come in as good as it did before i put it on a PCB. Thanks Again!

    Here are some pictures of my project.(note this is only my second PCB/first circuit i have built so soldering and such is a bit choppy <.<)

  • Advait

    Is the transmission supposed to be grainy and unclear? I am getting a very rough sound out of my fm radio. Also which electrolytic cap should I use? Does its capacitance matter? Can this project be done on a breadboard?
    Thanks in advance.

  • Advait

    Guys I have made the project now and it is quite stable except for the fact that the output is grainy. SOMETHING WEIRD I NOTICED IS THAT CHANGING THE ELECTROLYTIC CAP FROM 22 uf to 10uf DOESN’T EVEN CHANGE THE OUTPUT FREQUENCY! I don’t know how or why this happens, but when i changed the capacitors while while i was broadcasting something, i didn’t even have to tune the radio a bit to listen to it.
    Could somebody please tell me how to make the transmission more clear. I want it to be as clear as an official radio station.
    Thanks in advance

  • Advait

    Also, I have made this project on a breadboard and have not at all changed the measures of the different capacitors or resistors. The only thing I have changed is that my inductor was wound around something thinner than 1/4 inch and is therefore of lesser diameter. I have tried to compensate that by giving 5 turns of wire. Also I don’t know the AWG thickness of the wire I have used. Does this, in any way, affect the sound quality? Please help me improve the sound quality of my circuit.

  • Advait

    Hi

  • Advait

    How can i improve the quality of the output? I have made the circuit on a breadboard. The only thing i changed is that i made my inductor of a diameter thinner than 1/4 inch and to compensate that i put in 5 turns of wire instead of 4.
    The output is really grainy and unclear pls help me:)

  • Advait

    Pls help this for a science project i need it fast

  • Advait

    I am really sorry for thee repeated questions i have not done it purposely i just made this account yesterday and first when i asked some questions they werent showing up when i visited the page again and i kept on entering them out of confusion but now they seemed to have appeared i don’t know how this could have happened.
    I am relly sorry

  • Sybe

    Do you really need to use a ceramic disk capacitor for 0.01uF

  • Nathanael Beall

    can i simply replace the jack with a 2 pin mic condensor?

  • Lukas

    Amazing, am i the first to realise that it works just fine without any power/battery…
    This meant i could make a tiny adapter for my phone to play music to any radio!

  • Jcw608

    I do not have a bolt that size is there any other common item I can use to make the coil?