Difference between revisions of "Reading Temperature with AVR ADC"
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$$Temperature = ADCValue/2 $$ | $$Temperature = ADCValue/2 $$ | ||
| − | == | + | ==Hookup LM35== |
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==Code to Read Temperature== | ==Code to Read Temperature== | ||
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<script src="https://gist.github.com/Xplorer001/b5324c706391fa1e4a77.js"></script> | <script src="https://gist.github.com/Xplorer001/b5324c706391fa1e4a77.js"></script> | ||
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Revision as of 19:00, 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!
Contents
[hide]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 */
- }
Raw Data
Let's put all of the above together to read raw data from the ADC. We will connect a Potentiometer(Pot) to channel 0, vary it and read the raw voltage.
Hookup Pot
| #include "adc.h" | |
| #include "uart.h" | |
| int main() | |
| { | |
| int adcValue; | |
| float volt; | |
| ADC_Init(); /* Initialize the ADC module */ | |
| UART_Init(9600); /* Initialize UART at 9600 baud rate */ | |
| while(1) | |
| { | |
| adcValue = ADC_GetAdcValue(0); // Read the ADC value of channel zero | |
| volt = (adcValue*5.00)/1023; //10bit resolution, 5vReference | |
| UART_Printf("ADC0 Value:%4d Equivalent Voltage:%f\n\r",adcValue,volt); // Send the value on UART | |
| } | |
| return (0); | |
| } |
Temperature
Let's connect the LM35 temperature sensor to channel zero of the ADC and read the temperature. Resolution with 5V reference can be calculated as: $$ResolutionOfADC = (5v/1023)=4.887mv = 5mv$$ For every degree celcius the Lm35 provides 10mv voltage change, therefore $$Temperature = ADCValue/2 $$
Hookup LM35
Code to Read Temperature
| #include "adc.h" | |
| #include "uart.h" | |
| int main() | |
| { | |
| int adcValue; | |
| int temp; | |
| ADC_Init(); /* Initialize the ADC module */ | |
| UART_Init(9600); /* Initialize UART at 9600 baud rate */ | |
| while(1) | |
| { | |
| adcValue = ADC_GetAdcValue(0); // Read the ADC value of channel zero where the temperature sensor(LM35) is connected | |
| /* Convert the raw ADC value to equivalent temperature with 5v as ADC reference | |
| Step size of AdC= (5v/1023)=4.887mv = 5mv. | |
| for every degree celcius the Lm35 provides 10mv voltage change. | |
| 1 step of ADC=5mv=0.5'c, hence the Raw ADC value can be divided by 2 to get equivalent temp*/ | |
| temp = adcValue/2.0; // Divide by 2 to get the temp value. | |
| UART_Printf("ADC0 Value:%4d Equivalent Temperature:%dC\n\r",adcValue,temp); // Send the value on UART | |
| } | |
| return (0); | |
| } |