Difference between revisions of "Reading Temperature with AVR ADC"
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We will first initialize the ADC with the following code | We will first initialize the ADC with the following code | ||
# Enable ADC by Setting ADEN bit of ADCSRA and set the sampling frequency to half of oscillator frequency (i.e 8 MHz) | # Enable ADC by Setting ADEN bit of ADCSRA and set the sampling frequency to half of oscillator frequency (i.e 8 MHz) | ||
| − | # Select channel zero by default | + | # Select channel zero by default using the ADMUX register shown below. |
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'''ADC Multiplexer Select (ADMUX)''' <br/> | '''ADC Multiplexer Select (ADMUX)''' <br/> | ||
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|0||0||0||0||0||0||0||0 | |0||0||0||0||0||0||0||0 | ||
|} | |} | ||
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| + | <syntaxhighlight> | ||
| + | void ADC_Init() | ||
| + | { | ||
| + | ADCSRA=(1<<ADEN) | (1<<ADPS0); /* Enable ADC , sampling freq=osc_freq/2 */ | ||
| + | ADMUX=0x00; /* Result right justified, select channel zero */ | ||
| + | } | ||
| + | </syntaxhighlight> | ||
| + | Let us write another function to select the required channel and read the analog data as below : | ||
| + | # Select the required channel passed as input to the function | ||
| + | # Start the ADC conversion by setting ADSC bit in ADCSRA | ||
| + | # Wait till the conversion is over by checking the ADIF bit in ADCSRA | ||
| + | # Read the ADCW register and return the result of conversion | ||
| + | <syntaxhighlight> | ||
| + | uint16_t ADC_GetAdcValue(uint8_t v_adcChannel_u8) | ||
| + | { | ||
| + | |||
| + | ADMUX = v_adcChannel_u8; /* Select the required channel */ | ||
| + | DELAY_us(10); /* Wait for some time for the channel to get selected */ | ||
| + | util_BitSet(ADCSRA,ADSC); /* Start the ADC conversion by setting ADSC bit */ | ||
| + | |||
| + | while(util_IsBitCleared(ADCSRA,ADIF)); /* Wait till the conversion is over */ | ||
| + | /* ADIF will be set once ADC conversion is complete */ | ||
| + | return(ADCW); /* Return the 10-bit result */ | ||
| + | } | ||
| + | </syntaxhighlight> | ||
=Hook up= | =Hook up= | ||
Revision as of 18:13, 25 March 2016
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
- Enable ADC by Setting ADEN bit of ADCSRA and set the sampling frequency to half of oscillator frequency (i.e 8 MHz)
- Select channel zero by default using the ADMUX register shown 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 |
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 :
- Select the required channel passed as input to the function
- Start the ADC conversion by setting ADSC bit in ADCSRA
- Wait till the conversion is over by checking the ADIF bit in ADCSRA
- Read the ADCW register and return the result of conversion
uint16_t ADC_GetAdcValue(uint8_t v_adcChannel_u8) { ADMUX = v_adcChannel_u8; /* Select the required channel */ DELAY_us(10); /* Wait for some time for the channel to get selected */ util_BitSet(ADCSRA,ADSC); /* Start the ADC conversion by setting ADSC bit */ while(util_IsBitCleared(ADCSRA,ADIF)); /* Wait till the conversion is over */ /* ADIF will be set once ADC conversion is complete */ return(ADCW); /* Return the 10-bit result */ }