Introduction: Make a Pocket Sized FM Transmitter!
Have you ever been in a car or at work and you're tuned into the radio, and every five minutes the same playlist plays over and over again? As if repetition isn't bad enough they don't even seem to play anything you like? Or they play a song you like way to much and slowly you start to dislike it because of the high repeat rate? Or for some other reason you're just not feeling the radio. Well the solution is simple, just turn off the radio! Oh but wait what if you like music and want to continue listening in hopes of hearing a song you'll enjoy. well then you can play music from your phone or ipod! There is another issue, your speaker on your device isn't loud enough to fully enjoy :c. What if there was some way to use your radio as an amp for your device? As you might already know there is a way. well a few ways! You can sync your device through your car using a bluetooth feature! But what if you don't have that option? Don't worry! Out of all the questions I give you an answer! If you don't have a bluetooth sync feature on your car or radio then you can make your very own FM transmitter! As some of you may know FM transmitters can be purchased at stores online and locally but what is the fun of that? Would you want one off the assembly line or one of kind crafted by you for you? I like taking the DIY route for a lot of reasons. I hope since you're on a very well known DIY site you too share the same feeling! For those of you who don't know what a FM transmitter is, it is a device that transmits audio to a radio station. Now the one we will be making is low powered and has a range of about 10 feet. I have tested mine and I was able to get a perfect sound qaulity from my bedroom to my dinning room which is about ten feet if I had to guess. I made mine for work and it serves a great purpose! The best part about this one is it is pocket sized and fits very nicely into an altoids tin! A very popular choice of enclosures amongst the instructables community. If I have captured your attention and you would like to make one of these then please lets get started :)
Step 1: A Bit of More Info
This is a very rewarding build! You will find yourself using it quite a bit! I would like to explain some parts of this.
1- The altoids tin is used as the antenna! When I was trying to figure out what to put this circuit in once it is finshed I forgot about the antenna. Now, antennas are very usefull but some may find them unappealing. After I decided to use the altoids tin I thought I would have to run the antenna outside of the tin and while I understand the great purpose of antennas I was a little on edge about an antenna sticking out. It would look, less compact and all over the place. I then realized the tin can be used as the antenna! just connect the antenna from the circuit to the tin. The an-tin-a! I soldered the antenna wire to the inside of the lid. To my surprise solder flowed very well to the tin. Now since I am using the inside lid of the tin as the antenna there are some pros and cons. One pro is it looks nicer, a second pro, is if you open the tin the lid acts like dish and transmits a little better. Now there is one con. The tin can transmit audio very well using the lid as the antenna while being closed but in some cases I found that when it is closed there is some distortion and unwanted static, I have no idea as to why this happens but it doesn't all the time. But if it does happen simply open the tin and aim the lid towards the radio and it will work just fine :). This only happened on one radio (out of the four I have tested) so the odds of good sound quality while closed are good!
2- The heart of this circuit is the MAX2606. It is a very small IC. It is a surface mounted device (SMD) which can be very hard to work with if you have never soldered SMDs before, They can be very tricky. I have soldered SMDs in the past and after awhile it becomes easier. I much prefer though hole componets. If you have access to a solder flowing oven (hacked or bought) then SMDs aren't so scary. I was lucky enough to find a MAX2606 SMD soldered to a bigger PCB allowing for though hole soldering.
3- In order to tune your transmitter you need to turn the 10k pot and the 100k pot. It is very easy to tune but at the smae time the pots themselves are small and hard to turn and need to be turned with a flat head screw driver. I had a spare flat head bit and decided to add it to the tin as turning/tuning tool!
Step 2: What Is Needed and the Schematic
The MAX2606 needs 3 to 5 volts to operate anything more might destroy. I used a 5 volt regulator and a 9volt battery. The led is for power indication.
the rectangles are symbols for the resistors. the ones with an arrow is the symbol for the potentiometers. I know the resistor schematic symbol is more known as a 3 point like so -/\/\/\- but for ease I am using the other symbol which is simply a rectangle. Okay so aside from what is listed in the schematic you will need a PCB, 9 volt battery + snap, altoids tin, wire and all the tools that are common with electronics. Such as soldering iro, glue gun, wire strippers, dremel and everything in between. You will also need a 3,5mm plug. This is for connecting your phone and similar devices.
Step 3: Making for a Better Fit.
The PCB I have is too big for the tin and will stop 9 volt battery from fitting so I had to cut mine down for a better fit. It is wise to meausre and make modifications before we begin soldering the circuit. The left of the blue line on the PCB will have to be removed in order for the 9 volt to fit along with the circuit.
Step 4: Build the Circuit!
Start soldering the circuit! Solder from the inside out. I saved the 5volt regulator and led for last. I won't be walking you through the build of the circuit step by step because it is simple. I will however show some progression pictures of the build. The pictures are not meant for a guide because I did skip taking pictures. They are meant for just looking and observing, Try to keep all your componets as close as possible. I had to use some jumper wires inorder to complete connections. Odds are you will use jumpers too because this PCB isn't designed for any specific circuit. It is an IC PCB.
Step 5: To the Tin!
Time to move everything to the tin! I wanted to avoid making cuts and holes in the tin as much as possible. I could have mounted the led and switch to the tin but I liked the idea of keeping everything on the PCB. I ended up only making one hole on the tin. That hole was made to feed the 3.5mm through. After you make the hole for the 3.5mm insulate the tin. I used some cardboard. Then hot glue the 3.5mm in place then glue the circuit board in place. Now once everything is in place all that is left is the antenna, go ahead and solder it to the lid. Use hot glue to secure it.
Step 6: Done!
You are now ready to enjoy your music through any radio within range! turn it on near a radio and tune the pots until you hear your music! I hope you enjoyed this! If you have any questions feel free to ask!