OT: Hacking a BT/fm transmitter

So, I grabbed one of these off amazon. It's a a2dp bluetooth to fm stereo transmitter. It connects your phone/laptop to BT and broadcasts the audio but only on 108mhz...which I have learned most US stereos do not tune to! DOH!

So, I was hoping to figure out how to change the tx frequency but can't figure out what chip it is to even try to find a data sheet. I am assuming the small chip to the left is an AD8027 amplifier for the fm portion, but didn't see in the datasheet where I could adjust the frequency; more like it's just a booster. I believe the larger chip on the right is he BT chip (15470 8DP6476-16), but can't find a datasheet for it.

I need to get this thing to tx on a US frequency (88.1-107.9, odd decimals only).

If anyone has any suggestions, I sure would appreciate it!

I have a donor bt module out of an a2dp speaker and ordered some arduino bits to built a "custom" unit, but am messing about with this to learn new things.

Also, is there a more appropriate place to post these sorts of questions and reach *you guys? I don't want to make new friends or deal with another new forum unless I absolutely have to.

 

it should be externally programmable to do the standard us/canada center frequency channel allocations .
i do not have time to research the part pin-out at the moment .
i will have time after i get off work .

the ad8027 is a high bandwidth low distortion op-amp .
the other chip is the bt receiver/fm synthesizer .

need a better picture of the logo on the synth chip .

a problem with these cheapo modules is the re-branding of the ics .
or ... a supposedly custom or near custom modification of an existing design .

try this pdf :
https://encrypted.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjep53D7MHSAhVHOyYKHZz7CnYQFggbMAA&url=http://www.gigafu.com.tw/upload/2014Dec/pdf/201412191844031205931214_1.pdf&usg=AFQjCNF38zgvhABh3APKHFH0ZZ1uUcUR5g

page 14 has the pin assignments .

hmmm ...
something is not making sense ... or maybe it does .
i see no way to really "pin select" any of the frequency/channel allocations .
either this is not the right pinout or the unit is addressable via usb and software and this is how the parameters are changed .
it could be that the unit is "factory programmed" and that is the end of the story .

did the unit come with any software ?

also ...
as i make it out ...
the description leads me to believe the FM side is receive only .

 

No software came with it. Just the unit in a baggy (I removed the pcb from it's case to take pics).

So, you don't believe that data sheet is for the chip in the picture?
Page 12 has reference to a FM rx section and also a tx section, but I only see a call out for FM_RX on pin 4 but nothing for a tx

How did you find that data sheet? My knowledge is....growing. The best I could do was google the no. on the chip face with no result.

Also, for the sake of learning: if that datasheet was correct, then the chip would be 1.8v, so I would have to drop my line levels to 1.8v if I were going to try to access the UART pins?

Maybe at commands through a terminal? I know the HC05 bt modules used with arduinos are programmed through a serial terminal, I figured it would be a similar situation here?

LOL.
My chip is only 32 pins.
Datasheet is for 44+3. womp womp.

 

ok ... that will help ... 33 pins .
ehhh ... looking for this stuff requires a background in electronics/repair/design .
sometimes (as in this case) the number is almost correct but had i known the number of pins it would have been ruled out .
so , it is back to my original thought that the tx freq is selectable via jumpers or addressing
why they would put the freq at the top of the band is beyond me ... although most analog tuners will slide up to 108 MHz with no problem and the PLL type might just slew enough to lock on it .
either the thing has a power/cycle up default look-up table (on start , go to xxxx and read the data) or it is hard encoded (think prom or set during manufacture) or it is hard wired .

the correct data sheet would be the one to follow for determining the uart levels .
but normally , the addressing signal is not supposed to exceed the B+/- levels .

 

Might be this outfit. Logo is very similar.

https://www.nordicsemi.com/eng/Products

These might help
http://how-to.wikia.com/wiki/How_to_identify_integrated_circuit_(chip)_manufacturers_by_their_logos

https://www.elnec.com/en/support/ic-logos/?method=logo


maybe
http://www.axtal.com/cms/iwebs/default.aspx

 

need better picture of the ic in question .
there are logos that look very similar .

sometimes there is a sub-code that helps identify the original manufacturer .
rca and motorola were notorious for rebranding/subcontracting production/purchase and then stamping their own "in house" numbers on them .
this practice still happens today with many companies .

no time to go snooping yesterday ...
it was one of my two days off and i had much rat-killing to do .
picking up two comps for repair and putting in the back-ups was on the list .
and of course , one of the comps had not been updated or the *new* software installed .

as i make it out ...
the manufacturer is "ampak" ... based on a search of the part number ...
i have found the IC at "alibaba" from several distributors but finding the correct datasheet is like chasing a f**t through a keg of nails .

it might be that the ic was "rebranded" for a manufacturer of that module .
what is the name of the seller ?
what is the name on the unit ?
link to seller
a google search of "hacking a BT/FM unit" might be in order .

another idea ...
go to another forum such as "instructables.com" and look for a project similar to yours .
there are advantages to this , the biggest being documentation of the parts .

 

Yes indeed ...Choose the brand by the hackablity factor.

 

Definitely, Shawn! But this was $6 on amazon and I didn't realize that 108 was not tuneable on most US digital radios...

It's ok, though, I have a salvaged BT a2dp/avrcp module, arduino, i2c oled lcd, and an fm transmitter board (on the way).

Yes, that is more complicated than just buying a cheap and decent ready made unit, but I have to make things difficult! (and I'm messing about with arduino, right now, so it's good practice).

It looks like hacking this chip is just a bit outside my wheelhouse at this moment.

Thank you all for helping though, I still learned a few things on this thread!

 

i just thought of something ...
that unit might be illegal in the US .
i believe that the VOR for aircraft starts at about 108 MHz .
(as i recall , this is why the last allocated center channel on the fm broadcast band is at 107.9)
i might look that up later on .