madias wrote:Ahull: There are also smaller IC's for that, just google for 1.25 voltage reference shunt ic and you get back thousands of results like REF1112
I believe a bigger problem is, that there is no "real" VREF input on the maple mini's, so you need always a REF analog in pin and the need for a SW calculation (compare with another input pin). Correct me, if I'm wrong...
I think you are correct regarding the STM not having a suitable internal voltage reference, however you can roughly calibrate the STM by measuring its VCC and comparing with the 2V5 vref from one of these precision voltage sources.
A lot depends on how precisely you need to measure voltages. For example, with the Pig-O-Scope, you could trim and calibrate a bunch of resitive voltage dividers, and get acceptable precision for most hobby projects. If however you need ultra precise measurements, you would need to spend a bit more time, money and effort, and in those cases, the blue pills would not be a suitable choice, even if calibrated, due to the fact that the adc VREF is VCC, and they do not have a separate analog ground plane, and therefore noise is a significant factor.