26 ADC inputs

[TVan .8]

Which nucleo board should I use for 26 ADC inputs?

Or should I use a multiplexer? Can I get fast signal processing with a multiplexer?

Thanks

[Peter BENSCH]

Welcome, @Tom Van Gaever​, to the community!

STM32s have at least one to several physical ADCs, each of which always has multiplexers in front of it. Currently you could look at:

• NUCLEO-F303ZE
• NUCLEO-G474RE

The counter-question to the last question: how fast is "fast signal processing"?

In most cases, the switching and settling time of an ADC with a multiplexer is not short enough to meet this requirement. If you describe the requirements of your task, you might be able to get more detailed information.

Regards

/Peter

[TVan .8]

Thanks for your fast reply.

The microcontroller will be used for processing signals from a digital drum. So it only needs to be fast enough so there is no noticable lag for humans. This is in the order of milliseconds. It should be as fast as possible, because downstream processing of the signal will also add lag.

The NUCLEO-F303ZE looks promising. It seems to have 40 ADC channels and the slow channels give a conversion time of 0.21µs (is this with multiplexing?).

[Peter BENSCH]

Well, of course you must not only consider reading the inputs and downstreaming the output, but also the signal processing in between, which also takes time. Depending on the implemented filters and the resulting propagation delay, there can be clearly noticable audible lag, especially with slower microcontrollers such as the 72MHz STM32F303.

The 0.2µs are the minimum sampling time that you can realise with an ADC channel of an STM32F303 at an assigned input. Of course, multiplexing and the charge time of the internal capacitors caused by the source impedance must be added.

It may be helpful to look at RM0316, section 15 and at AN2834 so that the operation of the ADC becomes a little clearer?

Hope that helps.

Regards

/Peter

[TVan .8]

The source impedance should be very low, I'll be working with FSR and an opamp circuit.

So nucleo-f446ze would be a better option as it has a better processor speed. Only 24 input channels, but I can live with a few less inputs if it eliminates lag.

[S.Ma]

I would advise to check out the STM32G4 series as it is an STM32F3 successor

[TVan .8]

thx, this seems like the best option indeed