I just bought this board: https://www.sparkfun.com/sparkfun-audio-player-breakout-my1690x-16s.html
btw - you have a minor type in the hookup guide, it says Open the Library Manager tool, search for “SparkFun MY1690X MP3 Decoder” and install the latest version, it should be MY1690 not MY1690X.
the prod desc says “The MY1690X-16S operates over a serial-UART interface at 3.3V TTL”
When I wired up the board I used a esp32 board which supplied 5v to the audio play VIN pin, gnd and I attached wires to the audio boards rx and tx pins but did not connect them to the esp32.
I used a voltmeter to measure the VIN pin = 5v , then audio tx board pin = 3.2 but the audio board rx pin = 4.9 v.
I am worried if I connect the RX and TX pins to the esp32 it will burn out the pins. I think I may only need the rx pin but that is the one that is reading too high for the esp32 board.
Did i measure this correctly ? thanks