110 lines
2.9 KiB
C++
110 lines
2.9 KiB
C++
/*
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MAX6675.cpp - Library for reading temperature from a MAX6675.
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This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.
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http://creativecommons.org/licenses/by-sa/3.0/
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*/
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#include <MAX6675.h>
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MAX6675::MAX6675(uint8_t CS_pin, uint8_t SO_pin, uint8_t SCK_pin, uint8_t units)
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{
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pinMode(CS_pin, OUTPUT);
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pinMode(SO_pin, INPUT);
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pinMode(SCK_pin, OUTPUT);
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digitalWrite(CS_pin, HIGH);
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_CS_pin = CS_pin;
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_SO_pin = SO_pin;
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_SCK_pin = SCK_pin;
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_units = units;
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}
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float MAX6675::read_temp()
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{
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uint16_t value = 0;
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uint8_t error_tc = 0;
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float temp = 0.0;
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/*
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Initiate a temperature conversion. According to MAX's tech notes FAQ's
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for the chip, Line going high initiates a conversion, which means, we
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need to clock the chip low to high to initiate the conversion, then wait
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for the conversion to be complete before trying to read the data from
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the chip.
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*/
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digitalWrite(_CS_pin,LOW);
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delay(2);
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digitalWrite(_CS_pin,HIGH);
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delay(220);
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/* Read the chip and return the raw temperature value */
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/*
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Bring CS pin low to allow us to read the data from
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the conversion process
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*/
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digitalWrite(_CS_pin,LOW);
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/* Cycle the clock for dummy bit 15 */
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digitalWrite(_SCK_pin,HIGH);
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delay(1);
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digitalWrite(_SCK_pin,LOW);
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/*
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Read bits 14-3 from MAX6675 for the Temp. Loop for each bit reading
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the value and storing the final value in 'temp'
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*/
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for (int i=11; i>=0; i--) {
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digitalWrite(_SCK_pin,HIGH);
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value += digitalRead(_SO_pin) << i;
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digitalWrite(_SCK_pin,LOW);
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}
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/* Read the TC Input inp to check for TC Errors */
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digitalWrite(_SCK_pin,HIGH);
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error_tc = digitalRead(_SO_pin);
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digitalWrite(_SCK_pin,LOW);
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/*
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Read the last two bits from the chip, faliure to do so will result
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in erratic readings from the chip.
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*/
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for (int i=1; i>=0; i--) {
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digitalWrite(_SCK_pin,HIGH);
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delay(1);
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digitalWrite(_SCK_pin,LOW);
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}
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// Disable Device
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digitalWrite(_CS_pin, HIGH);
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/*
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Keep in mind that the temp that was just read is on the digital scale
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from 0˚C to 1023.75˚C at a resolution of 2^12. We now need to convert
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to an actual readable temperature (this drove me nuts until I figured
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this out!). Now multiply by 0.25. I tried to avoid float math but
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it is tough to do a good conversion to ˚F. THe final value is converted
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to an int and returned at x10 power.
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2 = temp in deg F
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1 = temp in deg C
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0 = raw chip value 0-4095
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*/
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if(_units == 2) {
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temp = (value*0.25) * 9.0/5.0 + 32.0;
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} else if(_units == 1) {
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temp = (value*0.25);
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} else {
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temp = value;
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}
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/* Output negative of CS_pin if there is a TC error, otherwise return 'temp' */
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if(error_tc != 0) {
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return -_CS_pin;
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} else {
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return temp;
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}
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}
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