On Sat, Jan 18, 2020 at 09:28 PM, Jerry Gaffke wrote:
Indeed, the $2 Blue Pill has two 12bit A/D's, good to 1 msps, up to 16 channels.??
Unfortunately, the raw specs can be misleading. The issue, typically, is noise which causes the lower bits of the ADC result to be garbage.
There is a figure of merit for ADCs called Effective Number of Bits (ENOB). ENOB is basically how many bits you can rely on to actually represent the signal at the input to the ADC. Some people have measured ENOB for Blue Pills and found that there are fewer "effective" bits than on a typical 8b Atmel Arduino board. 7? or 8 as I recall where I think the Arduino boards being measured were 8 or 9.
The speculation is that the culprit on the Blue Pill boards is the poor layout and 2 layer board. Apparently, the original LeafLabs Maple boards which used the same ST32 micro had better ENOB.
This is something to be aware of for almost all ADCs: the ENOB may be less than the actual number of bits even with the best board layout. This is due to noise in the chip itself. Standalone ADCs are (much) better. ADCs integrated into a processor SoC will have a worse ENOB than the "equivalent" standalone ADC and in no case will their ENOB match the published max. The SoC has its own sources of noise and on die "layout" issues. There are techniques to improve ENOB including turning off other functions (clocks) in the chip during sampling, and repeated sampling and averaging but be aware that published ENOB numbers may use those techniques (read: you will get a worse ENOB, unless you use them as well).
Of course, since most of us are buying the cheapest available clones from random suppliers with unknown quality the published numbers may be better than we can expect? :-)
A 72mhz 32bit ARM processor, 64kbytes of flash, 20kbytes of SRAM, lots of IO pins
Runs on 3.3v, so no need for level shifters talking to an Si4432.
Totally blows the doors off a Nano in every way.
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Now on the RPi, the (nonexistant) A/D is definitely not up to the Nano spec.?
Though I don't see where the tinySA needs an A/D.
True. I think this is just a useful thing to be aware of in general. To balance off as a "cost" against the $2 price of the Blue Pills when looking at other projects.
And would be easy to add an A/D as a peripheral if it is needed.
Jerry, KE7ER
On Sat, Jan 18, 2020 at 04:31 PM, Dragan Milivojevic wrote:
If memory serves me right more bits, more channels and sampling speed up to 2M so not sure what you mean?
