QN8027 FM Stereo Transmitter

The QN8027 is a high performance, low power, full-
featured single-chip stereo FM transmitter designed for
portable audio/video players, automotive accessories, cell
phones, and GPS personal navigation devices. The
QN8027 covers frequencies from 76 MHz to 108 MHz in
50/100/200 kHz step sizes for worldwide FM band support.
The QN8027 also supports RDS/RBDS data transmit.

 

OK, the datasheet makes this device sound interesting. But the datasheet is not really clear on how the device should be used and there is not much information on the web. Regardless, I purchased a few for a minuscule sum and set about interrogating the device with STM8eForth.

I'll publish my code on github soon but for now here is how I investigated the device:

1. bit bang an I2C interface
2. keep a local copy of all the devices registers so I could compare what I send the device with what it accepts and stores
3. some words to send one or more bytes while updating the local register copy
4. some words to retrieve one or all of the devices registers

This allowed me to 

1. reset the device
2. confirm the device registers when reset matched the datasheet
3. change frequency as desired 
4. put the device into transmit
5. send RDS groups
   

It didn't take long before I was successfully shuffling bytes to and fro. In the space of half a day I determined that I had a faulty crystal on one board, since fixed, a functioning FM transmitter (now two with the crystal changed) that I could change the frequency of and that after sending an RDS group the registers did not need to be reloaded if I wanted to resend the group since the contents were still there. 

I need to clean up my code to remove stuff I used for debugging and dispense with my local copy of the device registers.  I plan to post it onto github in a around 5-7 days time.

73's