Dave's FM Wireless MultiMusicCaster
I am a big fan of podcasts and music mp3 files, but listening to them on my computer is restrictive. I have to be in the computer room to hear them. If I want to visit my fridge, I then have to either pause the program or miss some of it. To get around this, I connected a small FM transmitter so I could transmit the program to a small FM radio that I could carry with me. This is my Podcaster Project.
I also built and described using a car FM Transmitter/MP3 Player at home. I've ended up with these little radio stations sprinkled all over the house! By tuning my FM portable radio, I pick the one audio feed I want to listen to. I wanted some audio feeds to loop my music 24/7 unattended, so I built (put together) some modules built in China.
The picture above shows the hardware I use for my MultiMusicCaster or MMC. Here are the
FM Portable Radio (one or more)
500mA 12VDC wall wart power supply with a female cigar lighter connector attached.
Three hole car power splitter adapter.
Multiple car FM Transmitter/MP3 players (I used 2).
FM Transmitter connected to an audio source.
All the pieces are shown connected as they are in operation. I have all the
transmitters set to different frequencies, separated by several channels to
prevent interference. Here is the band plan at the N2DS household:
87.8MHz FM transmitter connected to my computer.
88.3MHz Car MP3 Player with USB stick.
106.9MHz Car MP3 Player with USB stick.
107.3MHz FM transmitter connected to my internet radio.
107.9MHz FM transmitter connected to my cable box.
At this point, I ran out of audio sources. My pair of car FM transmitters are located near my cable box so the three units can be powered with one wall wart power supply. If you want more audio sources, I have seen 4 hole adaptors, and of course you can daisy chain several of these adaptors. I haven't measured the current flow of the car FM transmitters, but I understand the draw is about 75mA each. Make sure the output current of your wall wart power supply is within the needs of the transmitters.
The car FM transmitters each come with a remote control. If you use the controller, just hold your hand over the transmitter you don't want to control. I bought the car FM transmitters from eBay seller "emilyandlily". I like the narrow face of the transmitter, so they will fit in the cigar light adaptor also bought from "emilyandlily". (This seller ships from the U.S., so your wait is short.)
I should mention that there is an external audio input on these FM car transmitters, so these can be used instead of the FM transmitter if you need just the modulator part without the MP3 player. In my case, I already had the FM transmitters. I just checked and you can plug the car MP3 players in adjacent holes. The heads tilt so they don't bump in to each other.
The portable radio is a Tecsun PL-118, purchased on eBay for $20. The FM band is scanned for signals with all transmitters turned on and within range. By tuning the digital dial, you can jump from 87.5 up to 108MHz. So I set some transmitters at each end of the band, which is the quietest at this location. If your radio doesn't go quickly from the bottom to the top of the band, just set your transmitters all at one end. These FM transmitters can be set for any FM frequency and more!
I hope you enjoyed reading about my little project and it will give you ideas for yours. By the way, the transmitters can be purchased for around $4 each as well as the three hole lighter adaptor. The 12 volt wall wart power supplies are also available all over eBay, but make sure the filtering is good. Some power supplies are for charging only and are not filtered. My wall warts are 60Hz transformer types. I lightly load it so the filtering is good. I hope you enjoyed this article.
73, Dave – N2DS
Update! I added to my multimedia multiplex! I daisy chained another three hole lighter adaptor. I purchased two more car mp3 players. I like these because they will accept the micro SD (TF) memory cards without an adapter. I also changed the FM transmitter that is connected to my cable box to a USB power connection instead of the lighter plug connection. This is because there was a USB power connection on the 3 hole lighter adapter.
Including the two transmitters in other locations in my house, this makes 7 FM stations in my house! It probably breaks the rules on how many radio stations someone can own. :)
One final note: I stated I can hear these all over my house, which is true. But my house is smaller than most, even smaller than a mobile home. So if you are living in a big place, you may have to locate your transmitters in a central location.
… and I squeezed in another! I could daisy chain another 3 hole adaptor and add two more transmitters, but I think I've used up my 500mA wall wart capacity!
I felt it was time to shorten the wires and reduce the number of connectors. I took apart (easy) one of the 3 hole sockets and soldered the wall wart power supply wires directly inside. I cut the original power plug wire to a short length and put the housing back together (not easy). I cut the power connector off a second splitter and connected the wires to the first splitter. This gives me 6 holes plus 2 USB connectors.
Here is the complete mini-broadcaster as it is now. The players fit comfortably, and I have room for two more. Since the wall wart is only 500mA, I think I'll settle with this. Counting the two FM transmitters connected to my cable box and internet radio, this gives me 6 FM audio sources.
My 4 hole lighter adaptor arrived this morning from across the world. 4 transmitters plug in albeit a bit crowded. Nevertheless this makes a nice FM empire for me too without daisy chaining two adaptors together. There are also two USB connections on the front. Again, make sure you keep in mind the current rating of the wall wart before plugging in too many transmitters.
Update: I've had my little music center transmitters hooked up and running 24/7 for most of a year now. Unfortunately the displays have faded to nothing. Not a real big deal for the most part, as long as you don't mind searching the fm dial for the frequency of the transmitter, if you change it.
I also had one of the transmitters stop playing the sd card. I'll probably toss this, but the transmitter still works and I can feed external audio to it.
I think I'll switch off my system while not in use, or turn it on if I plan on listening to something while I attempt to sleep. I guess $3 doesn't buy perfection, even from China. In the car they are fine because they are on only while the car ignition is switched on. But this is a little heads-up on these devices. I'll just watch for them to be on sale and stock up at a few bucks each.
I was finally able to get this apart. (Getting it back together will be another story.) There is a 7805 voltage regulator with wires from the power connector near by. This is next to the USB connector. Can't figure out much more of this. Having seen inside this, I feel my life is now complete.