Reading Temperature with AVR ADC
Revision as of 18:04, 25 March 2016 by Sandeep (Talk | contribs)

The Atmega32 comes with a 10-bit, 8 channel inbuilt Ananlog to Digital Convertor (ADC). We will set it up and read temperature from LM35 and light with a simple (light dependent Resistor)LDR. So let's get started!

Basics

The ACSRA register allows us to enable the adc and set the sampling rate. ADC Control and Status Register A (ACSRA):

7 6 5 4 3 2 1 0
ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0
1 0 0 0 0 0 0 1

We will first initialize the ADC with the following code

  1. Enable ADC by Setting ADEN bit of ADCSRA and set the sampling frequency to half of oscillator frequency (i.e 8 MHz)
  2. Select channel zero by default. 
void ADC_Init()
 {
   ADCSRA=(1<<ADEN) | (1<<ADPS0); /* Enable ADC , sampling freq=osc_freq/2 */
   ADMUX=0x00;                    /* Result right justified, select channel zero */
 }

Let us write another function to select the required channel and read the analog data as below .


ADC Multiplexer Select (ADMUX)

7 6 5 4 3 2 1 0
REFS1 REFS0 ADLAR MUX4 MUX3 MUX2 MUX1 MUX0
0 0 0 0 0 0 0 0

Hook up

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