Como fazer interface serial ADC0831 com microcontrolador AVR (ATmega16) – (Parte 27/46)

How to make ADC0831 serial interface with AVR microcontroller (ATmega16) – (Part 27/46)

June 9, 2024 Roberto Magalhães

ADC is an electronic device that converts analog signals into digital numbers proportional to the magnitude of the voltage. ADC chips like ADC0804, ADC0809 etc. provide 8-bit digital output. The controller device needs eight pins to receive the 8-bit data (for more details about the ADC, see Using the AVR's Built-in ADC). Some applications need higher resolution ADCs (10-bit or greater digital data output) for data accuracy.

The use of parallel ADCs is an option for such applications. However, using parallel ADC will increase the hardware size as a 10-bit parallel ADC will have 10 output lines. Additionally, you may need to use a controller with a higher number of pins. The other option is to use a serial ADC, which requires fewer pins. Since data is transmitted serially, the data transfer rate of serial ADC is low compared to parallel ADC. They can serve as a very good alternative in applications where data transfer speed is not a critical point. This article explores the interface of the ADC0831 serial with ATmega16.

The ADC0831 is an 8-pin single-channel serial ADC that provides 8-bit data output. The input can be single-ended or differential type. Using the differential input option, A/D conversion can be performed for two different voltage levels. The function of each pin is described in the following table:

Fig. 2: Pin name and functions of serialADC0831

1. (Chip selection) – To start the conversion, a value from high to low is provided .

2. V _in (+) (Positive Analog Input ) – Positive voltage is applied to this pin. The input range for this is 0 to 5votls.

3. V _in (-) (Negative analog input) – Negative voltage is applied to this pin.

4. GND (Ground) – This pin is connected to the circuit ground.

5. V _reference (Reference voltage) – This pin is used to define the input voltage range of the ADC.

6. CLK (clock) – The clock pulse is supplied at the CLK pin for synchronization.

7. DO (data output) – This pin is an output pin of ADC, serial output data is available on this pin.

8. Vcc (power supply) – This is connected to the +5 volt power supply.

How serial ADC works:

Diagrama de blocos do ADC serial trabalhando com AVR

Fig. 3: Block diagram of serial ADC working with AVR

The above diagram shows a system in which the ADC device receives analog data from the transducer. The controller is used to control the ADC IC and process the converted digital data. The analog signal is given at the V pin _at (+). In differential mode, voltage at pin V _in (+) must be greater than V _in (-) otherwise the output data will not be generated by the ADC. Data conversion is initiated by giving a high to low pulse on the CS pin. In the first clock cycle, the ADC sends the '0' bit to the controller which shows that the following bits are the data bits. The MSB of the converted data is sent first. The timing diagram of the ADC0831 is shown below.

Diagrama de temporização do ADC0831 para comunicação serial em AVR

Fig. 4: ADC0831 timing diagram for serial communication on the AVR

Purpose: Convert the analog output voltage of the variable resistor into digital signals using ADC0831 and display it on the LCD.

Circuit Description:

Connection of ADC0831 with ATmega16 is shown in the circuit diagram. The variable resistor output is connected to V _in (+) and V _in (-) pin is grounded. The CS, CLK and DO pins of the ADC are connected to the microcontroller.

Programming steps:

1. Send a high-low pulse to the CS pin to initialize the conversion.

2. Monitor the status of the D0 bit until it goes low.

3. Send a clock pulse.

4. Receive data bits from DO pin of ADC 0831.

5. Store the data bits into a variable using bitwise operation.

6. When the data byte is received from the serial ADC, display it on the LCD.

Project source code

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// Program for ADC 0831 serial interface with AVR microcontroller (ATMEGA 16)

#include #include #include #define DO PD2 #define CLK PD1 #define CS PD0 #define lcdport PORT #define lol PB0 #define rw PB1 #define in PB2 empty lcd_init(empty); void lcdcmd(unsigned character); void lcddata(unsigned character); void adc_conversion(unsigned character); empty twi_init; unsigned character adc_read ; main int { unsigned character data (12) = "ADC OUTPUT:"; int i=0; unsigned character bits = 0; DDRA=0xFF; DDRB=0x07; DDRD=~_BV(DO); //The DO pin is the input pin and the rest of the pins are the output pins DDRC=0xFF; PORTD=0x07; lcd_init; while(data(i)!='�') { lcd data(data(i)); _delay_ms(5); I++; } while(1) { PORTD =(1< // high to low pulse is supplied to CS pin _delay_ms(1); PORTD&=~(1< _delay_ms(1); while(PIND & _BV(DO)) // waits until bit 0 is received { PORTD =(1< _delay_ms(1); PORTD&=~(1< _delay_ms(1); } PORTD =(1< // a clock pulse is supplied _delay_ms(1); PORTD&=~(1< _delay_ms(1); for(l=0;l<8;l++) { PORTD =(1< // data received when pulse is high _delay_ms(1); bits=bits<<1; //"bits" is a variable to store data. The shift left operation is performed to make room for the next bit if(bit_is_set(PIND,DO)) // if 1 is received bits =1; // bits are incremented by 1 PORTD&=~(1< //low pulse _delay_ms(1); } adc_conversion(bits); // } } /* this function is written to convert integer values to their corresponding ASCII value*/ void adc_conversion(unsigned character adc_out) { unsigned int adc_out1; int i=0; character position=0xC2; for(i=0;i<=2;i++) { adc_out1=adc_out%10; adc_out=adc_out/10; lcdcmd(position); lcddata(48+adc_out1); position--; } } empty lcd_init // function for initializing the LCD { lcdcmd(0x38); lcdcmd(0x0C); lcdcmd(0x01); lcdcmd(0x06); lcdcmd(0x80); } void lcdcmd(char unsigned cmdout) { lcdport=cmdout; PORTAB=(0< _delay_ms(10); PORTAB=(0< } void lcddata (output unsigned character data) { lcdport=dataout; PORTAB=(1< _delay_ms(10); PORTAB=(1< }

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