The aim of this project is to have a low power FM-Radio emitter that you could plug in any music device, and broadcast it's music through comercial bands. You have to know that it isn't totally legal, but I think that as long as you don't bother your neighbour it's ok.
Using this band allow you to use any radio tuner to receive your music, so you can listen to the same music all around your home, or wherever you have it plugged !

This are the features:
- FM modulation
- 2 AAA batteries
- f = 96.2 MHz
- -35dBV
- 6 x 4 x 2.5cm
- Mono

I had in mind this project for many days and finally I made it. I hope you'll enjoy it, at least as I did.

Step 1: Schematic and PCB

This circuit it's based on the FM BUG from talkingelectronics.com. Which has a first stage whith an BC547 as amplifier and a second stage with another BC547 as a modulator.

For designing it and fitting it into the size I wanted, I've used DesignSpark PCB, which is a free PCB editor and a nice thing about is that includes all the librearies for the footprints ans schematics of many devices.

I've attached the Schematic, the Layout and the Mask.

As you'll see this is the third version of it because the previous ones didn't fit in the case.

The Bill of Materials:

Component                     Value                      Qty
------------------------------------------------------------
2WPins                                                       4
BC547                                                      2
C                             1nF                          1
C                             5.6p                         1
C                             22n                          1
C                             22nF                         1
C                             27p                          1
C                             47p                          1
CP3                       2.2u                         1
L                            5 turns coil            1
r                             1M                           1
r                             4.7K                         1
r                             10K                          1
r                             22K                          1
r                             47K                          1
r                             470K                         1
------------------------------------------------------------
                                                          20
AND :

Box
mono minijack connector
female pins (some)
battery holder (for 2 AAA)
some wire
a LED

THE COIL:

for calculating the Coil dimensions I used an Android App called ElectroDroid where you set the frequency you want it to ressonate and it returns you the dimensions, and turns. The sixe of the coil is critical for setting correcty the frequency.

Step 2: PCB and CASE

To begin with, I printed the mask and proceeded to etch the PCB. I 've an isolator device, and an stiring case that helped me in the process and that I'm going to publish soon.

The next step has been the drilling and then the soldering of all the components on it.
Once having the board finished I tested all the connections, IT'S A VERY IMPORTANT STEP. And make sure there aren't any shorts.

Now was time to insert the board inside the box and decide where to drill the holes for the connectors. I used a draft to decide where they where going to go, but I had to modify some locations.