STM CircleOS forum / ADC speed setup

M_E · 2009-12-04 11:56:47

Hi

Has anybody some experiance when it comes to ADC frequency and sample time setup. Is it safe to run the ADC-clock in 32MHz, i.e. ADCPRE set to PLCK2 devided by 2. Will this speed generate accurate samples? How do you know what individual sample time to use for every channel, i.e. 1,5cycles, 55,5cycles...

I really need all the speed I can get for sampling and digital filtering.

Thanks

/M

Francis · 2009-12-09 16:32:07

Just a warning: we experienced problems when connecting several inputs on a single ADC, because of the internal capacitor. if you dont have to commute the input, it should work as fast as described in the datasheet.

brhans · 2010-03-04 14:10:35

I'd guess that the problems you saw when sampling different inputs is probably due to the fact that your analog inputs are connected to high-impedance sources - for example the 1M resistors in the Vbat voltage divider on analog channel 9.

This high resistance only allows a very small current to flow in or out of the pin, so correspondingly takes a relatively long time to charge the ADC's internal sampling capactitor.
If you sample faster than the time it takes to charge/discharge the cap when switching between channels then your readings will be incorrect.

If you construct a circuit to connect to the expansion connector and drive the CX_ADC1 and CX_ADC2 pins with a good low-impedance source (like an opamp), then you should have no trouble sampling these two analog channels (14 & 15) at a high rate.

Last edited by brhans (2010-03-04 14:11:17)

# 1 2009-12-04 11:56:47 ADC speed setup

ADC speed setup

# 2 2009-12-09 16:32:07 ADC speed setup

Re: ADC speed setup

# 3 2010-03-04 14:10:35 ADC speed setup

Re: ADC speed setup

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