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ADC Noise : too much

Question asked by Werner Meier on Jan 3, 2012
Latest reply on Apr 30, 2013 by Acelec
ADC Tests with stm32value eval board.
PC4 as AD Input, conversion all 20msec, 20turn Pot with 22k u1 RC Filter to PC4.
Software looks for max and min adc values. I let it run for 30000 conversions:
I get errors up to 16count at Zero, up to +16 / -40cnt at about half scale, -52count at full scale.
Sometimes the values are stable for some hundred conversions, then extremes hit.
I did the same tests with an old Keil STM32 board about 3 years ago with same results (but different software). The conversion is initialised with the slowes ADC conversion to minimize input impedance effects.
Has anybody found a solution (except filtering/averaging) / has anybody found similair behaviour.
Regards Werner

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