Hi, it is possible to use an external voltage reference for A/D conversion within the photon, despite it is set to 3.3V (just for reducing noise)? thanks
It is not possible to use a separate analog reference. The VREF+ and VREF- from the STM32F205 are not exposed on any pin on the Photon, and not even exposed out of the P0 (WM-N-BM-09) module.
I’d use an external I2C ADC for use with an external voltage reference or for higher resolution.