I just did some testing and my S355 buck converter seems to be the issue. When the power switch is off, the converter outputs precisely 5 volts. But when switched on, the converter periodically makes a slight humming sound and the voltage drops...
In my smart guitar project, I'm having some power problems with my T4, audio shield, and 0.96'' ST7735. Everything works fine when I supply power through USB, but if I supply power through a 9v battery and a 5v buck converter, the screen goes...