MAX6875 Temp Sensor example

libraries/MAX6675/MAX6675.cpp

@@ -0,0 +1,109 @@
+/*
+  MAX6675.cpp - Library for reading temperature from a MAX6675.
+
+  This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.
+  http://creativecommons.org/licenses/by-sa/3.0/
+*/
+
+#include <MAX6675.h>
+
+MAX6675::MAX6675(uint8_t CS_pin, uint8_t SO_pin, uint8_t SCK_pin, uint8_t units)
+{
+    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;
+}
+
+float MAX6675::read_temp()
+{
+    uint16_t value = 0;
+    uint8_t error_tc = 0;
+    float temp = 0.0;
+
+    /*
+      Initiate a temperature conversion. According to MAX's tech notes FAQ's
+      for the chip, Line going high initiates a conversion, which means, we
+      need to clock the chip low to high to initiate the conversion, then wait
+      for the conversion to be complete before trying to read the data from
+      the chip.
+    */
+    digitalWrite(_CS_pin,LOW);
+    delay(2);
+    digitalWrite(_CS_pin,HIGH);
+    delay(220);
+
+    /* Read the chip and return the raw temperature value */
+
+    /*
+      Bring CS pin low to allow us to read the data from
+      the conversion process
+    */
+    digitalWrite(_CS_pin,LOW);
+
+    /* Cycle the clock for dummy bit 15 */
+    digitalWrite(_SCK_pin,HIGH);
+    delay(1);
+    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);
+        value += digitalRead(_SO_pin) << i;
+        digitalWrite(_SCK_pin,LOW);
+    }
+
+    /* Read the TC Input inp to check for TC Errors */
+    digitalWrite(_SCK_pin,HIGH);
+    error_tc = digitalRead(_SO_pin);
+    digitalWrite(_SCK_pin,LOW);
+
+    /*
+      Read the last two bits from the chip, faliure to do so will result
+      in erratic readings from the chip.
+    */
+    for (int i=1; i>=0; i--) {
+        digitalWrite(_SCK_pin,HIGH);
+        delay(1);
+        digitalWrite(_SCK_pin,LOW);
+    }
+
+    // Disable Device
+    digitalWrite(_CS_pin, HIGH);
+
+    /*
+      Keep in mind that the temp that was just read is on the digital scale
+      from 0˚C to 1023.75˚C 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 ˚F.  THe final value is converted
+      to an int and returned at x10 power.
+
+      2 = temp in deg F
+      1 = temp in deg C
+      0 = raw chip value 0-4095
+    */
+    if(_units == 2) {
+        temp = (value*0.25) * 9.0/5.0 + 32.0;
+    } else if(_units == 1) {
+        temp = (value*0.25);
+    } else {
+        temp = value;
+    }
+
+    /* Output negative of CS_pin if there is a TC error, otherwise return 'temp' */
+    if(error_tc != 0) {
+        return -_CS_pin;
+    } else {
+        return temp;
+    }
+}