[SOLVED] PIC16F877a temperature control program using CCS C [if statement not executed]

[mnqobilozo]

i am designing a UPS for a school project using a PIC16F877A as a controller to monitor the temperature by displaying temperature on a 2X16 LCD and run a motor if a temperature of 70 degrees is reached and stops when the temperature drops to 50 degrees. i also inserted a voltage detector to detect an output on the inverter and send a 5 volts signal to PIN_B2 of the pic if voltage is present, so that if there is no voltage, the pic should switch a relay through PIN_B4 to supply the load from the mains supply bypassing the UPS.
i have succeeded on the other tasks but i fail to switch the relay accordingly.

here is my program written in C language using CCS compiler.

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Code C - [expand]
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/* 
PIC16F877A and LM35 Based Temperature Monitor 
 
MACHI M.C 
STD.no 20403715
*/ 
 
#include <16f877a.h> 
#device adc=10    // Set ADC resolution to 10Bit
#fuses XT,NOLVP,NOWDT,NOPROTECT 
#use delay(crystal=4000000)
#use rs232(baud=960,xmit=PIN_C6,rcv=PIN_C7,ERRORS)
#include <lcd.c>
 
#define  LOAD  PIN_B7
#define  THRES 70.0     // load switching threshold in Celsius
#define  OFF 50.0  // fan stops when temparature reaches value in degrees
#define ADC_OFF 0   // ADC off
#define  RELAY PIN_B4
#define  R2    PIN_B2
#define  R1    PIN_B1
#include <stdlib.h>
int16 digital_reading;  // ADC resolution is 10Bit, an 8Bit integer is not enough to hold the reading
float temp;
 
 
 
void main()
{
  
   /* ADC Initialization */
   setup_adc(ADC_CLOCK_INTERNAL); // initialize ADC with a sampling rate of Crystal/4 MHz
   setup_adc_ports(RA0_ANALOG);   // set PIN_A0 as analog input channel
   set_adc_channel(0);            // point ADC to channel 0 for ADC reading
   delay_ms(1);                   // ADC module is slow, needs some time to adjust.
  
   disable_interrupts(GLOBAL);   // DISABE ALL INTERRUPTS.
   SET_TRIS_B(0X0F);             //set RB0,RB1,RB2 & RB3 as inputs, RB4,RB5,RB6 & RB7 as output.
 output_low(RELAY);            // relay initialy off
   if (input(PIN_B2)==0)
   {
   output_high(PIN_B4);
   }
   else if (input(PIN_B2)==1)
   {
   output_low(RELAY);
   }
   
   /* Peripherals Configurations */
   lcd_init();                   // Turn LCD ON, along with other initialization commands
   output_low(LOAD);             // the load is initially OFF
   lcd_gotoxy(1,1);              // point LCD cursor to col1 row1
   lcd_putc("Temperature is:");  // print on LCD
   {
   while(1) // infinite loop
   {
      digital_reading = read_adc();    // capture current temperature reading
      delay_us(100);                   // 0.1ms delay for ADC stabilization
      temp = digital_reading * 0.4883; // convert reading to Celsius
      lcd_gotoxy(1,2);                 // point LCD cursor to col1 row2
      printf(lcd_putc,"%2.1f C",temp); // print value on LCD
 
      if(temp>=THRES)
       Do 
       {
         output_high(LOAD);   // Control Load
       }
      while (temp>=OFF);
      else  output_low(LOAD);
      delay_ms(1000);   // 1 second delay between readings
   }
   }
}

---

 

[milan.rajik]

Do you have a transistor driving the relay? PIC cannot supply current needed by a relay if connected directly to PIC.

 

[mnqobilozo]

Do you have a transistor driving the relay? PIC cannot supply current needed by a relay if connected directly to PIC.

yes i do. for the statement:

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Code C - [expand]
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if (input(PIN_B2)==0)
   {
   output_high(PIN_B4);
   }
   else if (input(PIN_B2)==1)
   {
   output_low(RELAY);
   }

---

the pic executes output_high(PIN_B4) not accounting the statement if (input(PIN_B2)==0).

 

[hemnath]

Split the code into several parts to debug the code.

Post your schematic.

In your code, you are checking the PIN_B2 once. Did you measure the voltage on PIN_B2 is high or low with a multimeter.

Do a blink LED test, it will solve 90% of your problem.

Best wishes

 

[betwixt]

I'm only using a mobile phone to read the message so I can't check easily but it looks like the ADC conversion is returning a number which you then convert to volts by multiplying by 0.4883. That is correct for volts but the LM35 returns 10mV/C so unless you are amplifying the voltage it may not be reaching the threshold you expect.

Brian.

 

[mnqobilozo]

Thank you all for your replies guys. my problem is solved. the program expected the conditions to be true in order to proceed to the next statement. i solved it.