Convert Belkin FM Transmitter from Battery Power to Car Power

I have one of the original Belkin Tunecast FM transmitters for my iPod. After I fed it one pair of AA batteries I decided I needed a better way. So, here's how I converted a car cigarette lighter cell phone charger into a method of powering my transmitter. This instructable is with a Belkin, but it will work for any transmitter, or even any battery powered thing-a-majiggy that you want to change from battery power to car/cigarette lighter power.

A bit of electrical explanation :
AA batteries put out 1.5 volts, since my FM transmitter uses two AA batteries: 2 * 1.5v = 3 volts

I used a LM317 variable output voltage regulator so I had to rig up some resistors to get the right output. If you use an LM317, the formula to determine the output is :
(Voltage out) = 1.25 * (1 + (R2/R1))
Where R1 and R2 are connected as shown later.

Step 1 Disassemble cigarette lighter adapter

Disassemble your cell phone charger and pull out the circuit board, desoldering as needed. You typically start by unscrewing the metal tip and shaking out the fuse and spring. Then, pry the two plastic halves apart. Be careful when you pull the pieces apart as there is sometimes more than one spring inside and it can go flying. Make sure you keep the fuse, spring, and connecting wires.

Comments

[twocvbloke]

The later model Tunecasts have an external supply input, aswell as the option to select exactly what frequency you want to use, so the TC1 is pretty much junk in my opinion, the TC3 is good, but has an annoying habit of cutting out with quiet music, but the TC2 is the best for modding, as you can take out the audio cutout nonsense, you can add an external antenna and power it from an external supply... :)

[darc]

No argument from me. The TC1 pictures here was a little old when I decided to tear it apart. I should get a newer one, I just have a hard time tossing out something that works for me... though when I'm in big cities and local stations start cutting into all 4 channels, I get pretty angry. -darc

[Lee Wilkerson]

I have this same model. Here's how I addressed the swamp-out issue (other signals interfering with mine).
I opened the case, turned my home stereo on one channel, and carefully touched the end of a 10 ft. (3 m.) piece of thin (about 24 ga.) insulated wire to different places inside 'til I found the place which gave me the best signal level on the stereo. Turns out to be one of the battery leads. I then cut a little notch in the case for the wire to exit and tucked it behind the inside edge trim of my windshield (my radio antenna is on the passenger-side front fender). No more swamp-outs when driving downtown. :)
I would have done an 'ible on it, but it's simple enough. Besides I plan on making a much better signal coupler later at the same time I make a semi-permanent installation with the power adapter.

[twocvbloke]

That's why I like my TC3 (when it's not cutting out my music when it goes quiet), you get the full range from about 89-107.9Mhz, so you can scan your local frequencies on your radio the pick the one with the most static... :) You can get a cheap TC2 or TC3 on ebay, and then sell off your old TC1 on ebay (if you can reverse the modification safely), there's always someone after an FM transmitter, as some places have little or no radio coverage, either through distance or topography, so they can utilise one of the TC1's 4 frequencies... :)

[mike_d214]

(removed by author or community request)

[darc]

Yeah, if you just want to attach your own antenna, then you can desolder the blue wire (sometimes labeled ANT on the board) and hijack it. There are other instructables about bypassing an inductor on the circuit board to improve transmission, but I've not been able to locate the specified inductor on this model.

[mike_d214]

awesome thanks. Yeah, somehow I didn't see the "ant" label.

[fenacv]

I just got one of this last week. But yesterday I found it's onsale here $15 off.
http://www.pricebat.ca/Belkin-MP3-CD-MD-FM-Transmitter-3-5mm-Plug-2-AAA-Batteries.p_10049603/
...oooooops

[Pie_eata]

sweet idea, I modded mine just like that cept I added a decent antenna

[darc]

Did you have the same model transmitter as me? The instructables I looked at for adding a better antenna noted that it wouldn't work with this model, but I haven't actually taken it apart and examined the circuit board to confirm that claim.

[Pie_eata]

it does wonders for mine ( the same 1 in the pix)

[brauhaus]

I've been contemplating something similar, although, looking at re-using a car cell phone charger for the power source. Figure this could save me the trouble of building the voltage regulator and stuffing it inside the cigar adapter. I have an old one around that I think puts out 3v.

[darc]

That would save some time and money, the one I had (that I used to house the voltage reg) output 5v so it was no good : ( It was an old off-brand Nokia charger, probably from around 2001.