Question

(a) Find the resolution for a microcontroller anadlog to digital controller (ADC), if the accuracy is 54.6mV and the ADC is powered using 7 volts [5 marks] (b) If the ATmega16 microcontroller is using a clock frequency of 3 MHz, what are the fastest and slowest frequencies for the ADC unit? (5 marks] (c) A microcontroller is interfaced with an analog sensor at pin 2. Using figure Q4c() and Tables Q4c(i) and Q4c(ii),write a C code that will correctly configure the microcontroller based on the following specifications The maximum voltage output of the sensor is 5 volts Right adjustment of the output result. . The clock of the microcontroller is 4MHz, and the ADC will need a clock frequency of 31.25 kHz. . Disable interrupt .A gain factor of 10. Disable auto-trigger. [10 marks

Answer 1

Hello

Here are the answers

a)

If you need to resolve 54.6mV on a 0-7V input range, that gives use a adc resolution of 7/0.0546 = 128 counts . The resolution for this would be 7 bits since 2^7 = 128.

b)

We know that

ADC clock frequency = XTAL frequency / Prescaler

In the microcontroller we’re discussing, prescaler values of 2, 4, 8, 16, 32, 64 & 128 are provided.

Hence

Slowest Frequency= 3 Mhz / 128 = 23.4 Khz

Fastest Frequency= 3 Mhz/2 = 1.5 Mhz

c)

Here i have assumed an AVR microcontroller.

#include <avr/io.h>

void ADC_Init() {

DDRA=0x0; /* Make ADC port as input */

ADCSRA = 0x87; /* ADC Enable and prescaler=128 since 4Mhz/31.25 Khz = 128 */

ADCSRA |= (0<<ADIE); /* disable interrupts */

ADMUX = (1<<REFS0)| (1<<MUX3)) /* Vref: Avcc, ADC channel: 0 and gain factor of 10x by setting MUX 4:0 bits to 01000 through the reference table*/

ADCSRA |= (0 << ADSATE); /* ADC Auto Triggering disable */

}

Hope this helps. Thumbs up to help back.