For the second version of the board, my first intent was to do another STM32F4 DISCO daughter board. But then I thought, why not design a standalone board?

Routing and soldering a LQFN100 package seems quite a challenge for me because I never designed such a complex board and I basically didn’t have any experience with surface mount components. There’s also a lot more components: power supply, audio DAC, decoupling, oscillator, etc.

But who doesn't like a good challenge? So I decided to do the standalone board and I also to add a battery charging circuit, an SD card and a small OLED screen for good measure :)

For the audio DAC, I tried to find a component with a friendly package that doesn’t require hot air soldering (like TSOP, LQFN). I found a couple of those but they don’t have headphone amplifier or input ADC so In the end I went for the SGTL5000 (QFN16), also because it’s used on the Teensy audio board so I have a reference design to start from.