Analog-digital converter

An analog-to-digital converter (ADC) is a hardware component that converts analog input signals into digital values. Usually the conversion is done with a certain accuracy, which is specified by the number of bits. The RP2040 is equipped with a 12-bit ADC by default, but with MicroPython the ADC is internally converted to 16 bits.

\[V_{digital} = V_{analog} \cdot \frac{V_{sys}}{Resolution ADC} = Value \cdot\frac{3.2V}{2^{16}} \label{eq:adc1}\]

To convert the digital values into analog quantities such as voltage or current, a conversion function is used. With a 16-bit conversion function, the input voltage is converted according to the equation \eqref{eq:adc1}, where $Value$ is the measured input value in volts.

Listing filter method

def getfilteredADC(self):
    '''Sample and filter adc data'''
    self.filtered[0] = self.filter1.calc()
    self.filtered[1] = self.filter2.calc()
    self.filtered[2] = self.filter3.calc()
    self.filtered[3] = self.filter4.calc()

The getfilteredADC() method in listing is a function in the MPPTController class that is used to sample the voltage and current data from the ADCs and smooth it through filtering. This involves filtering the raw data from the four ADC channels. The filtering is necessary to filter out measurement inaccuracies of the ADC. The method first calls the calc() method of the FilterAvg object for each ADC channel to get the filtered data. This filtered data is then written to the filtered array of the MPPTController class, which is later used by the calcADCData() method to calculate the voltage values.

Listing calculate adc data

def calcADCData(self):
    '''Calcuate raw adc data to voltages and currents'''
    self.voltage[0] = round( corr[0] * self.filtered[0] * adcScaleFac
                                                        * voltDiv, rounded)
    self.voltage[1] = round( corr[2] * self.filtered[2] * adcScaleFac
                                                        * voltDiv, rounded)
    self.current[0] = round( corr[1] * ((( self.filtered[1] * adcScaleFac)
                                                - zeroCurrentHall) / 
                                                currentSensivity), rounded)
    self.current[1] = round( corr[3] * ((( self.filtered[3] * adcScaleFac)
                                                - zeroCurrentHall) /
                                                currentSensivity), rounded)
    self.power[0] = round(self.voltage[0] * self.current[0], 2)
    self.power[1] = round(self.voltage[1] * self.current[1], 2)

The calcADCData() method from Listing in the MPPTController class is used to convert the raw ADC data into voltage and current values. For the voltage measurement, a voltage divider with resistors of 36 kOhm and 2.2 kOhm is used, where voltDiv specifies the divider factor from equation \eqref{eq:adc1}. The factor adcScaleFac gives the conversion factor. The converted voltage values are multiplied with correction factors corr and rounded. For the current measurement the transfer function from the last chapter is used.