As they say success comes through hard work. So I had these car FM transmitters laying around. I wanted to know, what made them tick. I ripped it wide open and started marking chip names down. With some logic I quickly determined the chip that was responsible for FM transmissions.
Name of the chip? – BK1085
So the implementation is simple enough. To my knowledge it’s just a one chip wonder. Audio comes in and it is modulated and spit out from the other side.
Datasheet is helpful. Every piece of information is available right there. The chip itself can be for example controlled over I2C. You can change the frequency, time out periods, mute etc.
So I started probing, first experiments went well. Then later I took the chip and placed it upside down, made some wrong connections and the magical smoke came out – blimey.
Then I took another FM transmitter and ripped that apart. It had the same chip but the package was different. So I soldered it out, made a little test/development board. Turned it on and nothing!
Haven’t looked into that much anymore maybe in the future, when some inspiration strikes me. Also I ordered two transmitters so we will see where that leads us.