We haven’t shared the board layout yet, but all of the necessary information is in the schematic. The aux ADC on the Mayfly is the ADS1115. Its Vcc is tied to the 3.3v supply of the board, so it’s not possible for it to sample anything greater than that. You can use the jumpers near the Grove connectors on the board to provide a 5v excitation for external sensors, but the sensor must not return a signal greater than 3.3v. For all of our deployments, we use sensors that have 5v excitation but provide a 0-2.5v return. If your sensor returns 5v, you can simply use a resistor divider to change the voltage to something within the safe range of the ADS1115.