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SOFTWARE TECHNIQUES FOR COMPENSATING ST7 ADC ERRORS

2 SOFTWARE TECHNIQUES

2.1 AVERAGING TECHNIQUE

Averaging is a simple technique where you sample an analog input several times and take the

average of the results. This technique is helpful in eliminating the effect of noise on the analog

input or wrong conversion.

As we take the average of several readings, these readings must correspond to the same an-

alog input voltage. You should take care that the analog input remains at the same voltage

during the time period when the conversions are done. Otherwise you will add digital values

corresponding to different analog inputs and introduce errors.

In other words the analog input should not change in-between the different readings consid-

ered for the averaging.

It is better to collect the samples in multiples of 2. This makes it more efficient to compute the

average because you can do the division by right-shifting the sum of the converted values.

This saves CPU time and code memory needed to execute a division algorithm.

For example take 8,16, 32 samples etc., and then take the average.

Figure 1. Graphical representation of Averaging technique

Practical measurement

To obtain the results, this averaging technique is used to measure the voltage on one of the

microcontroller’s analog input pins. A total of 16 conversions is taken and the average is cal-

culated. This is done in a loop in the firmware.

Digital

Output

Number of Conversions

Average

Value

AN1711 Datasheet(PDF) 8 Page - STMicroelectronics