Belkin is a popular manufacturer of cheap and cheerful computer accessories, having singlehandedly made the USB hub sexy! One of their more popular product hitching the iPod popularity ride, is the Tunecast II FM Transmitter.
It is only earlier this year (2007) that FM transmitters like these became legal in the UK, ignoring the fact that savvy netizens have already brought theirs from eBay.
This modification improves the transmission range and remove the 'feature' of auto-power down when no audio signal is present. It certainly sets you up as resident pirate radio DJ of your block and allows you to jam the loud radio listener on a bus or train!
Please note that this is a rehash of something that was done before 'instructable' came along. No more the delay now for the good stuff!
Product link:
http://catalog.belkin.com/IWCatProductPage.process?Product_Id=263200
It is only earlier this year (2007) that FM transmitters like these became legal in the UK, ignoring the fact that savvy netizens have already brought theirs from eBay.
This modification improves the transmission range and remove the 'feature' of auto-power down when no audio signal is present. It certainly sets you up as resident pirate radio DJ of your block and allows you to jam the loud radio listener on a bus or train!
Please note that this is a rehash of something that was done before 'instructable' came along. No more the delay now for the good stuff!
Product link:
http://catalog.belkin.com/IWCatProductPage.process?Product_Id=263200
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Signing UpStep 1: How to gut the TuneCast
Those ever efficient Taiwanese manufacturer manage to secure this piece of gadget with just a single screw, if you're handy with a screwdriver, that's the job done!
The first image shows the location of the screw (ignore the switch for the moment, that comes later), the second one shows where to a gentle pry will open it, note the plastic latch.
The first image shows the location of the screw (ignore the switch for the moment, that comes later), the second one shows where to a gentle pry will open it, note the plastic latch.
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I tried a reception test just touching a contact attached to a wire to various components (starting from what I think was the chip-side of the inductor) but could not improve reception.
The only thing that did was the lower right pin of the chip on the rear (marked 1 on first pic below), so I soldered my wire to that. Now I get reception up to about 25m away through several brick walls (having got about 5m out of the box if I was lucky). My wire is about 1.5m long, and I didn't experiment for the optimum length, as it works (and this is to be used inside a house anyway).
As for the auto power-off mod, that went wrong too! I fluffed the solder a bit to the top-right contact point, and it seemed to disappear leaving no metal to contact. Doh! After a bit of experimentation, I found that the same lower right leg of the other component (marked 2 in pic below) when jumpered to the resistor right next to it (marked 1 in pic) put the Tunecast into an always-on state. I settled for that, as again this is to be used in the home, it only uses about 2w, and I am powering it from a transformer anyway so I don't have to mess about with batteries.
Thanks for the guide anyway!
I used a different method to boost the output power, which will work not only for the Belkin Tunecast, but for ANY transmitter which uses a BH1415F, or even any other Rohm FM transmitter chip. Instead of trying to figure out what components were involved in the filter/attenuation network, I used a soldering iron and a toothpick to lift and disconnect BH1415F pin #11 (RF output) from the board. Then I soldered a quarter-wave wire antenna directly to the pin, which gives direct access to the maximum possible output power. Make sure the wire is secured so an accidental tug won't rip the pin off the IC; I used a generous application of super glue to attach the wire to the board near the connection. If a transmitter uses a different Rohm FM transmitter chip than the BH1415F, look up the datasheet to find out which pin is RF output.
The real gold in this Instructable is the auto power-off disable. I've been using this transmitter to listen to music from my computer anywhere in the house, and have been looking for a good way to disable the auto power-off. Up until now, I've been doing it by running a separate copy of Winamp that plays a subsonic or ultrasonic burst for two seconds, every 30 seconds in a loop. It worked, but on some radios you could hear a slight distortion when the burst played. This may still be a useful option for people who aren't comfortable soldering, or who have a different transmitter.
I just performed your auto power-off disable mod, and it works great! Though I did make one change. The pad you're getting power from appears to be active only once the transmitter is powered up, which still requires an initial audio input. So instead, I connected the transistor pin through a 1M resistor directly to the positive pin of the DC power jack. If you're looking at the board from the LCD side, with the power connector on the bottom, it's the second pin from the left between the large SMD capacitor and the LCD (verify it with a voltmeter if you're unsure you have the right one). The transmitter now turns on immediately when power is applied, and stays on indefinitely; regardless of audio input.
Finally, one more tip. Loop the power and audio input cables a few times through a ferrite toroid filters out hum and hiss. You can use one toroid, but it's easier to use two, one for each wire. The more loops, the tighter the windings, and the closer to the transmitter, the better it works. A clamp-on style ferrite should work almost as well, though I haven't tried. Obviously, don't loop your antenna through a ferrite, as this will attenuate the signal. If you haven't added your own separate wire antenna, skip the toroid for the audio cable, as it contains the antenna.
With these changes, I'm very happy with the performance of this transmitter; and its range and quality rival any consumer or kit transmitter I've tried for less than $100.
A bit about the Rohm FM chip... Before these iPods, many FM transmitters came in kit form, and the Rohm chip was the first to be highly integrated and made it easy to build these. And I think you could get single chip (with earphone amps) FM radio tuner too.
It is a great little FM transmitter isn't it. In terms of fidelity, if you get it right, FM transmitter still kind of sound better than Bluetooth speakers. Heh, kind of please there's still a purpose for this old instructable. Cheers!
Slip a metal putty knife or screwdriver blade between the darker (or may be metallic) oval trim and the plastic case and pry it off. There are three screws underneath. Remove them and you're in.
It looks to me like they put the FM signal on the ground, so your USB cable and your audio cable are acting like an antenna. Probably best to find the RF output pin and connect directly to that.
Is been a while since this trheat was open, anyways I have the same gadget and like 'mdphoenix'' mentioned is correct about opening it.
Now I have a question of my own, not sure if the gadget is the same circuitry is yours..
I need to find the tiny inductor and bypass it to attache antenna.
Thanks and Regards
Wil.
Thanks and Regards
Wilson
The first experiment was to extend the antenna. I cut the blue antenna line at 2cm. Soldered a line of 80cm to it. Result: worse than the original tunecast2.
Second experiment: I removed the old antenna (just ripped it off) and soldered a new line to the board on another position, see picture below. Much better result than my first experiment, however, I cannot tell if it's better than the original tunecast2.
Please do not laugh at my soldering technique/result, I'm not very good at this i'm afraid :-)
Third experiment. Note that this step cannot be undone. Using a knife, I cut away that small white thing below my new antenna. It did not seem to make things better or worse. I forgot to make a picture of this, and currently I'm too lazy to reopen the device and take a picture
Tomorrow I'll drive 200+km and will let you know if it made things better or not.
Michel
* I drilled a hole to lead the antenna out of the enclosure directly
* Make sure that the sigaret lighter in your car is tightened securely so it cannot move
* make sure that the antenna cable and the power cable are separated well.
These three all caused interference. Having found this out, it makes the Tunecast useable.
But it did not work.
I am going to try again once I get some time. I will post something here if I get it to work. (there are inductors in different places, so I do not know that I did the right one)
Thanks.
I can't see the equivalent components to bypass the auto shut down either.
http://www.xmfan.com/viewtopic.php?t=3257
They even shipped it to me in the UK with no problems. I would really recommend it 100%.
the british electronic chain store.
finally someone who mentions stuff you can buy in the UK.
most instructables are american or written for americans.
i bought one of thes transmitters from Tesco, for 7 quid last week, and it seems that the best quality is at the bottom on the fm band, and the best signal is at the top.
ive been also looking for some way of extending the arial, to give it extra range. i was going to increaser the output wattage, but i remembered that it might blow the diodes.
anyway, what i find funny, how mine is technika, and your is belkin, and they both look near enough the same, and have near enought the same layout.
good instrictable otherwise, keep it up. ;)