/*
MAX6675.cpp - Library for reading temperature from a MAX6675.
Created by Ryan McLaughlin <ryanjmclaughlin@gmail.com>
*/
#include <Arduino.h>
#include <MAX6675.h>
MAX6675::MAX6675(int CS_pin, int SO_pin, int SCK_pin, int units, float error)
{
pinMode(CS_pin, OUTPUT);
pinMode(SO_pin, INPUT);
pinMode(SCK_pin, OUTPUT);
digitalWrite(CS_pin, HIGH);
_CS_pin = CS_pin;
_SO_pin = SO_pin;
_SCK_pin = SCK_pin;
_units = units;
_error = error;
}
float MAX6675::read_temp(int samples)
{
int value = 0;
int error_tc = 0;
float temp = 0;
for (int i=samples; i>0; i--){
digitalWrite(_CS_pin,LOW); // Enable device
/* Cycle the clock for dummy bit 15 */
digitalWrite(_SCK_pin,HIGH);
digitalWrite(_SCK_pin,LOW);
/* Read bits 14-3 from MAX6675 for the Temp
Loop for each bit reading the value and
storing the final value in 'temp'
*/
for (int i=11; i>=0; i--){
digitalWrite(_SCK_pin,HIGH); // Set Clock to HIGH
value += digitalRead(_SO_pin) << i; // Read data and add it to our variable
digitalWrite(_SCK_pin,LOW); // Set Clock to LOW
}
/* Read the TC Input inp to check for TC Errors */
digitalWrite(_SCK_pin,HIGH); // Set Clock to HIGH
error_tc = digitalRead(_SO_pin); // Read data
digitalWrite(_SCK_pin,LOW); // Set Clock to LOW
digitalWrite(_CS_pin, HIGH); //Disable Device
}
value = value/samples; // Divide the value by the number of samples to get the average
/*
Keep in mind that the temp that was just read is on the digital scale
from 0ËšC to 1023.75ËšC at a resolution of 2^12. We now need to convert
to an actual readable temperature (this drove me nuts until I figured
this out!). Now multiply by 0.25. I tried to avoid float math but
it is tough to do a good conversion to ËšF. THe final value is converted
to an int and returned at x10 power.
*/
value = value + _error; // Insert the calibration error value
if(_units == 0) { // Request temp in ËšF
temp = ((value*0.25) * (9.0/5.0)) + 32.0; // Convert value to ËšF (ensure proper floats!)
} else if(_units == 1) { // Request temp in ËšC
temp = (value*0.25); // Multiply the value by 0.25 to get temp in ËšC
}
/* Output -1 if there is a TC error, otherwise return 'temp' */
if(error_tc != 0) {
return -1;
} else {
return temp;
}
}
thanks for your helps...
...
tags added.
