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Exercise 9: Analogue to Digital (ADC) and Digital to Analogue (DAC) conversionIntroduction | ||||||||
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Checking linearityIf we connect the DAC output to the input of an ADC channel and we slowly ramp up the DAC value from 0 to its maximum and we read back the signal level with the ADC, then we expect a perfectly linear curve. This is true under the condition that both, the DAC and the ADC are perfectly linear. | ||||||||
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As we can see, the curve becomes very non-linear for values above 200 (3.3V * 200 / 256 ~ 2.6 V). Unfortunately we do not know if the ADC or the DAC is responsible for this non-linearity. We need an external ADC to check. We also see that the line does not pass though 0,0 as it should.
Verifying linearity with an external ADS1115 | ||||||||
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Here is a graph when fitting a polynomial of grade 5 | ||||||||
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