Bluetooth FM Transmitter for Your Car/Home





Introduction: Bluetooth FM Transmitter for Your Car/Home

About: I like to find out how things work. I like to see if I can learn new things through that.

This is my first instructable so go easy on me. I thought of creating this device a while back and am now sharing my idea with you. Have you ever had a vehicle without BLUETOOTH built in? What about one without even an AUX input? Here is where my creation comes in to play. Most of us already have an older BT headset from before just sitting in a drawer collecting dust, some may even have the FM transmitter required for this build sitting in that same drawer collecting dust as well.

This is my concept on a CHEAP and relatively EASY to build BLUETOOTH/FM TRANSMITTER for your vehicle which can also be used at HOME!!! ( Total cost if you don't have any of the pieces is < $30 )


Items you will need for this build -
Bluetooth Headset - ($5 to $15 on Ebay)
FM Transmitter - ($5 to $10 on Ebay)
Seatbelt Cushion - ($3 at WalMart)

Items you might decide to use -
Soldering Gun - (not necessary if you use electrical tape)
Hot Glue Gun - (not necessary but helpful in placing the items at the end)
Electrical Tape - (if you will not use the soldering gun)
Extra Wire - (if you plan on extending pieces)
Extra battery - (if you plan on powering the devices longer)

Once these items have been procured, you are ready for STEP 1!!!

ONE THING I WOULD LIKE TO NOTE IS THAT I HOT GLUE/SOLDER/ELECTRIC TAPE WRAP ALL MY JOINTS, YOU DO NOT HAVE TO, I DO JUST TO MAKE SURE MY JOINTS DONT COME APART. Just wanted to get that out of the way as you will see this over and over through my pictures.

Step 1: Extracting the Bluetooth

Gently begin to take apart the Bluetooth housing. Be extra careful to NOT damage any wires from the MAIN BOARD to the speaker/microphone components. My Bluetooth did not come with any screws, it just "SNAPS" back together.


Step 2: Extracting the FM Transmitter

These devices usually have screws under the batteries (inside the battery compartment). Locate and take out the screw (you may have more than one) holding the casing together. The internal pieces should come right out. No prying is necessary as these are usually held in place by the screws.

If you are using the Transmitter I am you will have to cut the leads to the battery case or un-solder them (which is what I did)

Step 3: Removing Components - Bluetooth Speaker

Now that you have the Bluetooth out of its case along with the FM transmitter, locate the SPEAKER wires from the Bluetooth as these will be attached to the input of the FM transmitter. Cut the wires as close to the speaker so you have the greatest length to attach the wires from the FM transmitter (label + and - ends if possible, red is always +).

OPTIONAL - It was at this point that I decided to extend the microphone on the Bluetooth device so later it can be placed where it fits best for voice clarity.


Step 4: Connecting the SOUND

Connect the + side of the Bluetooth speaker wire with the L and R wires from the FM transmitter. Connect the - side of the Bluetooth speaker wire with the - or GROUND for the FM transmitter. Cut a small slit so you can see the wires exposed and attach extended wires long enough to reach your Bluetooth. Solder the joints or you can use electrical tape so they don't come apart (I did both).


Step 5: Connecting the SOUND - OPTIONAL


Using the 1N4001 diodes we can connect the Bluetooth to both L and R speakers. The diodes only allow flow of current forward but does not allow current to flow back. We will place these diodes on the L and the R connections coming from the FM Transmitter board. Cut a small slit so you can see the wires exposed and attach extended wires long enough to reach your Bluetooth. Solder the joints or you can use electrical tape so they don't come apart (I did both).

When the diodes have been placed, connect the IN portion of the diodes together and solder a single wire to those ends (this wire goes to the Bluetooth + terminal of the speaker). Attach the G (ground) cable from the transmitter to the G cable from the Bluetooth and using electrical tape, wrap the joints so they don't come apart (again, I soldered, then used tape to isolate the terminals).

Step 6: Replacing the Battery

The next step is more of a decision, you may keep the current battery from your Bluetooth (3.7V output is common) to power your devices but it will impact the overall functional time of the device since it will also power the FM transmitter. You will be able to recharge your battery with the charger from your Bluetooth, the one from your spare battery (you must keep the connector), or the one that came with the FM transmitter (I will be using the one from the FM transmitter).

Attach the GROUND or - cable of the battery to the ground power cables on both your Bluetooth and FM transmitter then solder/tape it. Then attach the POSITIVE or + cable of the battery to both your Bluetooth and FM transmitter then solder/tape it.


Step 7: CHECKING POWER - We Dont Want to Fry Your Devices

Ok, so far so good, we should have the AUDIO OUTPUT from the Bluetooth directly connected to the L/R speakers from the FM transmitter. Make sure these are connected to the ports labeled L and R, not the + and - because we will see smoke when we connect the battery.

You should also have all three (3) ground cables connected together, one from the Bluetooth, one from the FM Transmitter and one from the battery. Make sure to wrap the cables with electrical tape if you opt not to solder the joints.

(I hot glued the buttons back to the FM transmitter and the shell to the BT to use the buttons also)

If you have this and it looks like this picture, you are on your way, you may pass GO and proceed to the next step. If not, please check your connections, I don't want you to fry any devices before you get to experience the fruits of your labor.

Step 8: The Broadcast Test

If everything seems to be working properly, lets give it a whirl... Ensure your phone is connected to the Bluetooth by synching to it. Make sure your FM transmitter is ON by checking the light (also check what frequency is broadcasting on).

Tune in your radio on your car or home and make a phone call. VOILA!! you should be able to hear your phone call through your speakers!!!

If you have difficulty hearing the call, you can opt to add a larger antenna to your device. Look for the ANT port on the FM transmitter and attach a longer wire to it or, an actual antenna like I did. This will increase the reception to your stereo.


Step 9: Shoulder Mounting

Ok, the shoulder pad installation was easier than thought. You will need a hot glue gun or you can opt for some glue (but regular glue is messy).

A.) Take your shoulder pad and lay your components on top, arrange the components to how you feel will fit best. All components are different but you will want the Bluetooth microphone to rest about half way through the shoulder pad for best results.

B.) Open your shoulder pad from one end and turn it inside out.

C.) Lay the FM transmitter down with hot glue so it stays in place, make sure to cut out the screen so you can see it on the outside. Hot glue down the extended battery if you opted for one.

D.) Before gluing the Bluetooth down, check the button placement so they are reachable. You will have to re-use part of the Bluetooth shell if you don't want to deal with making buttons. I left the Bluetooth device outside to make it easier for the buttons to be pressed. You can leave it on the inside for better conceal ability.

E.) Make sure the recharge wire (whether wire or Bluetooth charging port) are easily accessible so you can re-charge any time.

F.) Flip the shoulder pad back to regular, you should be able to see all the buttons are easily accessible and hot glue close the side you opened.

Step 10: Enjoy!!!

DONE, mount the device on your cars seat belt and turn it on, make sure your phone is sync'd with the Bluetooth device and enjoy your conversations coming directly from your speaker system on your vehicle or home!!!



Glovebox Gadget Challenge

Runner Up in the
Glovebox Gadget Challenge



    • Creative Misuse Contest

      Creative Misuse Contest
    • Water Contest

      Water Contest
    • Clocks Contest

      Clocks Contest

    16 Discussions

    Are you guys first off I just want to say I really admire your page and everything that you guys build it's just amazing creativity. With that being said I'm going to build one of these tomorrow and hopefully someone can get back to me sooner than later just so I can be sure although I'm sure it mentioned it I'm using the traditional FM transmitter that takes the two AAA batteries with a little female headphone jack out of it and an old Bluetooth headset, correct ?
    The main thing I want to be able to do is utilize my cell phone to connect to the Bluetooth headset so that I can use the FM transmitter to connect to the radio. Hopefully not too many of your laughing but if this is what that will do just a little reassurance I will put it together tomorrow about her right now how works out thank you all for your information and thorough instructions!

    1 reply

    Sorry for not getting back to you yesterday. How did the project go? By now you have your answers but just in case...

    What you have described is exactly what this does, connects your phone via Bluetooth to the Headset which is connected to the FM transmitter broadcasting the signal through FM to your vehicles stereo.

    The only extra thing is to play a bit with the length of the antennae as it makes a difference, too much and you will get much static as well as too little. There is a formula out there but I don't have it right now.

    Hope that helps! Hope it works for you.

    Great 'ible! One recommendation is to use capacitors instead of diodes. Diodes only permit flow in one direction. For an AC audio signal, you will be cutting half of the signal; even though you may not notice anything on lower quality systems (like over the radio). Capacitors will isolate the channels from a dc current flow (if there is a dc bias), and keep some separation in case the Bluetooth receiver dislikes shorting the channels directly. I would recommend at least 8 volt

    1 reply

    I guess I hit the "reply" by accident half way through my message... But I recommend capacitors rated at least for 8 volts and around 470uF should be plenty to not clip the bass. If electrolytic put the positive toward the Bluetooth device.

    Cool. I was wondering why it was fuzzy and then I read more. I like the shoulder mount idea. It is very original.

    1 reply

    Thank you. I made it because I have an older Toyota truck and it does not have any inputs on the stereo. I use shoulder pads from time to time so it was only logical to use it as the mounting device. :)

    Thank you for your comment.

    Very well done. I like the placement on the seat belt cover, a lot better looking than some clunky thing on the dash.

    1 reply

    Thank you. The shoulder pad was the logical location as I don't care for extra things on the dashboard either. Plus its easily detachable and very light weight so you can put it up or take with you anytime.

    Thanks for your comment.

    Hi, don't the diodes in the analog audio circuit cause distortion? Audio, by nature is both positive and negative. By blocking the negative swing, you are causing distortion?

    1 reply

    So far I tested the sound with and without and did not hear a difference, if there is distortion it was not noticeable to me. We are only blocking the flow of the audio back in from the L and R inputs.

    The upside is they allow the feed only from the BT to the FM transmitter and they stop the AUX input from crossing both L and R (Stereo) sound as it would if you were to just attach the cable direct.