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PaxInstruments / labwiz-board

A development board based on the STM32 series processors specifically targeting the STM32F103RxT series.
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Analog reference #14

Closed charlespax closed 8 years ago

charlespax commented 8 years ago

What should we do with VDDA?

charlespax commented 8 years ago

We could leave it unconnected, butI have it connected to 3.3V. It can be completely ignored. However, it someone wants to play with using an external analog reference, there is a voltage on that pin.

screen shot 2016-05-20 at 00 22 54

There is a good deal of space in the area near VDDA. We could add a footprint for a precision voltage reference and just leave it unpopulated. screen shot 2016-05-20 at 00 26 12

electrokean commented 8 years ago

Adding the ferrite in https://github.com/PaxInstruments/labwiz-board/issues/48 would allow someone to remove that and isolate VDDA to connect in an alternate reference.

charlespax commented 8 years ago

I like that idea. We should probably have a ferrite bead there anyway. If there's enough room, I can also add the appropriate IC footprints on the backside of the board.

An alternative approach would be to have a voltage reference on a module board. The reference can be measured by one of the GPIO pins (they all are on an ADC) for calibration of the STM32's internal reference.

charlespax commented 8 years ago

To keep the design simple I will not implement this. To get quality analog readings an external reference can be used to calibrate the STM32 12-bit ADC or a higher quality ADC can be connected through a digital interface. Closing issue.