AVR Freaks

Thanks so much!

The wires would be pretty long (like 3 metres each), so noise would be a big problem.

Can four DS18S20 be used to feed the digital input to the ATMega16 and display the results directly (without AD conversion?)

Good idea, sparrow, I'll try that in practical situations.

Thanks David for the informative reply. It seems I'm stuck with the pricey digital sensors. Oops. Because I intend to measure the temperature of a compressor motor, the condenser, the evaporator and room temperature. The compressor (0.5HP) would generate a lot of noise, right?

I can shorten the length of wires to 1 metre or somewhat less, by settling for inconvenience; still the money saved by avoiding expensive digital sensors is well worth it.

But the concern is, even if the wire were short, would the compressor interfere?

I just broke off a lead of the only LM35 I had, while desoldering it in a hurry. I'll need to wait for a day or two for another LM35 to arrive in the mail, and I'll check it practically by placing it near the compressor, by the Atmega16 thermometer we designed today.

Meanwhile, I'll read up more on the codes and datasheets. :)

EDIT: I have an ammeter monitoring the motor current.

Thank you, David. Fortunately, the evaporator remains at 15-20C positive. So it wouldn't be a problem, right? :)

I was searching and found a digital DS18B20 at a much cheaper price than expected. I guess we can use digital in this project. Should I order four of them?

Yup, I have an over current protection by a C type 5 Amps MCB. Though it's not that reliable.

I worry about the amount of Freon Charge and fluctuating room temps in the summer and its effect on the compressor. :)

That's a great information that a little capacitance in the wire would actually smoothen down the spikes. Didn't occur to me.

David, I'm kind of a cheapskate sometimes.    I'll buy properly shielded wires, though. But I guess I can skip the long, 3 metres of wire for the sake of less interference and accuracy. I'll mount the LCD and microcontroller IC near the cooling unit.

When I get another LM35 by mail, I'll test how the LM35 works with a metre or so of shielded cable with the compressor running.

In the meantime, I'm trying to figure out how to modify this code David has written for me, in order to accommodate 4 sensors polled in turns. My C proramming knowledge has rusted away after college.

/*
 * bagho.c
 *
 * Created: 23/04/2015 13:51:50
 *  Author: David Prentice
 */

#include <avr/io.h>             // special function registers
#include <stdio.h>              // sprintf()
#define F_CPU 4000000           // you are running on 4MHz RC
#include <util/delay.h>         // _delay_xx()
#include "lcd.h"                // Fleury LCD library

int main(void)
{
    char display[32], degree = 0xDF;         // special character for degree symbol
    int tempC, tempF;
    ADCSRA = (1<<ADEN)|(7 << ADPS0);        // Enable, div128
    ADMUX = (3 << REFS0)|(1<<ADLAR)|(0<<MUX0);  // VREF=2.56V, 8-bit, channel #0 is on PA0 pin

    lcd_init(LCD_DISP_ON);
    lcd_puts("Temperature is");       // only print this once
    while (1) {
        ADCSRA |= (1<<ADSC);          // Start Conversion
        while (ADCSRA & (1<<ADSC));   // wait for completion

        tempC = ADCH;                 // 10mV per C.  full-scale is 2.56V i.e. 256C
        tempF = (tempC * 9) / 5 + 32;

        sprintf(display, "%3d%cC %3d%cF", tempC, degree, tempF, degree);
        lcd_gotoxy(3, 1);             // 4th column, 2nd line
        lcd_puts(display);            // string is all printed in one go
        _delay_ms(500);
    }
}

I'm trying to multiplex two LM35 sensors at first.

 I know the code might be wrong in many ways, but am I going the right way? Please guide me.

#include <avr/io.h>             // special function registers
#include <stdio.h>              // sprintf()
#define F_CPU 16000000           // 16 MHz clock set
#include <util/delay.h>         // _delay_xx()
#include "lcd.h"                // Fleury LCD library

int main(void)
{
 char display[80], degree = 0xDF;         // special character for degree symbol
 int tempC
 ADCSRA = (1<<ADEN)|(7 << ADPS0);        // Enable, div128, ADC clock at 125 KHz
 ADMUX = (3 << REFS0)|(1<<ADLAR)|(0<<MUX0);  // VREF=2.56V, 8-bit, channel #0 is on PA0 pin

 lcd_init(LCD_DISP_ON);
 lcd_puts("Compressor");          // only print this once
 while (1) {
  ADCSRA |= (1<<ADSC);          // Start Conversion
  while (ADCSRA & (1<<ADSC));   // wait for completion

  tempC = ADCH;                 // 10mV per C.  full-scale is 2.56V i.e. 256C
  

  sprintf(display, "%3d%cC", tempC, degree);
  lcd_gotoxy(2, 1);             // 2nd column, 1st line
  lcd_puts(display);            // string is all printed in one go
  _delay_ms(500);
  
  ADCSRA|=(1<<ADIF);                // Clearing ADC.

   return(ADC);
 }
 
 void Wait()
{
   uint8_t i;
   for(i=0;i<100;i++)
      _delay_loop_2(0);
}

int tempD
 ADCSRA = (1<<ADEN)|(7 << ADPS0);        // Enable, div128, ADC clock at 125 KHz
 ADMUX = (3 << REFS0)|(1<<ADLAR)|(1<<MUX0);  // VREF=2.56V, 8-bit, channel #1 is on PA1 pin

 lcd_puts("Condenser");          
 while (1) {
  ADCSRA |= (1<<ADSC);          // Start Conversion
  while (ADCSRA & (1<<ADSC));   // wait for completion

  tempD = ADCH;                 // 10mV per C.  full-scale is 2.56V i.e. 256C
  

  sprintf(display, "%3d%cC", tempD, degree);
  lcd_gotoxy(2, 2);             // 2nd column, 2nd line
  lcd_puts(display);            // string is all printed in one go
  _delay_ms(500);
  
  ADCSRA|=(1<<ADIF);                // Clearing ADC.

   return(ADC);
 }
 
 void Wait()
{
   uint8_t i;
   for(i=0;i<100;i++)
      _delay_loop_2(0);
}
}

Wow! Wow and triple wow! You know what? You are a mark of true genius! Your program worked like a charm, right off the bat!
 

Now I do not know how to thank you enough for your efforts and help, and for tutoring me all the way. 

I'll buy a pencil today and write your programs in my diary, and go through them over and over again to know how stuff works, and then make a code that'd average the ADC in four successive measurements.

A few messages with a wise person is worth more than a few years of learning! Oui!

PS: You brought be a step closer to demolish my fears of building an AVR oscilloscope! (I'm a cheapskate, remember? 25,000 INR is too much for an industrial oscilloscope.)  

PC sound card!! Wow that's a cool idea!! Thanks a bunch!! :D

Shall try it today. Would 3V input be too much?