The CSR8645 is a legendary chip in the DIY audio world. Produced by CSR (Cambridge Silicon Radio), which was acquired by Qualcomm in 2015, it was the “gold standard” for mid-range Bluetooth audio for years.
The CSR8645 is a “System-on-Chip” (SoC), meaning it handles the radio, the processor, and the audio output all in one.
The CSR8645 is ROM-based. While you can change settings (like the Bluetooth name, EQ curves, and button functions) using a USB-to-SPI programmer and the “CSR8600 ROM Config Tool,” you cannot write custom code to it. It’s a “what you see is what you get” chip.
If you are designing a DIY speaker, it is a solid, albeit aging, choice. Here is the technical breakdown you need.
Market Position: It was incredibly popular because it was one of the first affordable chips to offer aptX support (CD-quality audio over Bluetooth) and integrated ROM-based configurations. You’ll find it in countless mid-range headphones and Bluetooth receivers from the mid-2010s.
https://www.instructables.com/CSR-Bluetooth-Module-Programming/
https://www.amazon.com/Comimark-CSR8645-Bluetooth-Lossless-Amplifier/dp/B07X2JNT53