AVR®: Using and Testing the ADC

 In this video:

  • Provide a block diagram overview of the AVR® MCU's 10-bit Successive Approximation ADC.
  • Input voltage reference options and input channels.
  • Discuss prescale and conversion timing requirements, keeping the ADC clock between 50 & 200 kHz, setting a prescalar of 64, since we have a F_CPU = 8 MHz.
  • Set the range of the ADC by setting the voltage reference (to AVcc).
  • Open a new project and setting writing ADC_init ( ), using the datasheet as a coding reference.
  • Choose ADC1 as ADC input channel, connected to port C1 on the ATmega328P Xplained mini.
  • Configure the options in the ADC status and control register & ADC Auto Trigger Enable (ADATE).
  • Toggle an LED in the ADC ISR, so that we have a line of code to set a breakpoint on.
  • Connect a potentiometer to vary the voltage on the ADC pin.
  • Debug to verify the register configuration.
  • Example reading on the ADC result register: 0x156, or 342.
  • Vin = ADC * Vref / 1024 = 342 * 3.297 = 1.1011 measured by ADC, 1.104 measured by voltmeter, so 2.9 mV error or 1 LSB.
  • AVR120: Characterization and Calibration of the ADC on the AVR MCU.
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