Tasmota/tasmota/xsns_39_max31855.ino

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/*
xsns_39_max31855.ino - MAX31855 thermocouple sensor support for Tasmota
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Copyright (C) 2020 Markus Past
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifdef USE_MAX31855
#define XSNS_39 39
bool initialized = false;
struct MAX31855_ResultStruct{
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uint8_t ErrorCode; // Error Codes: 0 = No Error / 1 = TC open circuit / 2 = TC short to GND / 4 = TC short to VCC
float ProbeTemperature; // Measured temperature of the 'hot' TC junction (probe temp)
float ReferenceTemperature; // Measured temperature of the 'cold' TC junction (reference temp)
} MAX31855_Result;
void MAX31855_Init(void){
if(initialized)
return;
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// Set GPIO modes for SW-SPI
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pinMode(Pin(GPIO_MAX31855CS), OUTPUT);
pinMode(Pin(GPIO_MAX31855CLK), OUTPUT);
pinMode(Pin(GPIO_MAX31855DO), INPUT);
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// Chip not selected / Clock low
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digitalWrite(Pin(GPIO_MAX31855CS), HIGH);
digitalWrite(Pin(GPIO_MAX31855CLK), LOW);
initialized = true;
}
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/*
* MAX31855_GetResult(void)
* Acquires the raw data via SPI, checks for MAX31855 errors and fills result structure
*/
void MAX31855_GetResult(void){
int32_t RawData = MAX31855_ShiftIn(32);
uint8_t probeerror = RawData & 0x7;
MAX31855_Result.ErrorCode = probeerror;
MAX31855_Result.ReferenceTemperature = MAX31855_GetReferenceTemperature(RawData);
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if(probeerror)
MAX31855_Result.ProbeTemperature = NAN; // Return NaN if MAX31855 reports an error
else
MAX31855_Result.ProbeTemperature = MAX31855_GetProbeTemperature(RawData);
}
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/*
* MAX31855_GetProbeTemperature(int32_t RawData)
* Decodes and returns the temperature of TCs 'hot' junction from RawData
*/
float MAX31855_GetProbeTemperature(int32_t RawData){
if(RawData & 0x80000000)
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RawData = (RawData >> 18) | 0xFFFFC000; // Negative value - Drop lower 18 bits and extend to negative number
else
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RawData >>= 18; // Positiv value - Drop lower 18 bits
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float result = (RawData * 0.25); // MAX31855 LSB resolution is 0.25°C for probe temperature
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return ConvertTemp(result); // Check if we have to convert to Fahrenheit
}
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/*
* MAX31855_GetReferenceTemperature(int32_t RawData)
* Decodes and returns the temperature of TCs 'cold' junction from RawData
*/
float MAX31855_GetReferenceTemperature(int32_t RawData){
if(RawData & 0x8000)
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RawData = (RawData >> 4) | 0xFFFFF000; // Negative value - Drop lower 4 bits and extend to negative number
else
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RawData = (RawData >> 4) & 0x00000FFF; // Positiv value - Drop lower 4 bits and mask out remaining bits (probe temp, error bit, etc.)
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float result = (RawData * 0.0625); // MAX31855 LSB resolution is 0.0625°C for reference temperature
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return ConvertTemp(result); // Check if we have to convert to Fahrenheit
}
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/*
* MAX31855_ShiftIn(uint8_t Length)
* Communicates with MAX31855 via SW-SPI and returns the raw data read from the chip
*/
int32_t MAX31855_ShiftIn(uint8_t Length){
int32_t dataIn = 0;
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digitalWrite(Pin(GPIO_MAX31855CS), LOW); // CS = LOW -> Start SPI communication
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delayMicroseconds(1); // CS fall to output enable = max. 100ns
for (uint32_t i = 0; i < Length; i++)
{
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digitalWrite(Pin(GPIO_MAX31855CLK), LOW);
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delayMicroseconds(1); // CLK pulse width low = min. 100ns / CLK fall to output valid = max. 40ns
dataIn <<= 1;
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if(digitalRead(Pin(GPIO_MAX31855DO)))
dataIn |= 1;
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digitalWrite(Pin(GPIO_MAX31855CLK), HIGH);
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delayMicroseconds(1); // CLK pulse width high = min. 100ns
}
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digitalWrite(Pin(GPIO_MAX31855CS), HIGH); // CS = HIGH -> End SPI communication
digitalWrite(Pin(GPIO_MAX31855CLK), LOW);
return dataIn;
}
void MAX31855_Show(bool Json){
char probetemp[33];
char referencetemp[33];
dtostrfd(MAX31855_Result.ProbeTemperature, Settings.flag2.temperature_resolution, probetemp);
dtostrfd(MAX31855_Result.ReferenceTemperature, Settings.flag2.temperature_resolution, referencetemp);
if(Json){
ResponseAppend_P(PSTR(",\"MAX31855\":{\"" D_JSON_PROBETEMPERATURE "\":%s,\"" D_JSON_REFERENCETEMPERATURE "\":%s,\"" D_JSON_ERROR "\":%d}"), \
probetemp, referencetemp, MAX31855_Result.ErrorCode);
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#ifdef USE_DOMOTICZ
if (0 == tele_period) {
DomoticzSensor(DZ_TEMP, probetemp);
}
#endif // USE_DOMOTICZ
#ifdef USE_KNX
if (0 == tele_period) {
KnxSensor(KNX_TEMPERATURE, MAX31855_Result.ProbeTemperature);
}
#endif // USE_KNX
} else {
#ifdef USE_WEBSERVER
WSContentSend_PD(HTTP_SNS_TEMP, "MAX31855", probetemp, TempUnit());
#endif // USE_WEBSERVER
}
}
/*********************************************************************************************\
* Interface
\*********************************************************************************************/
bool Xsns39(uint8_t function)
{
bool result = false;
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if(PinUsed(GPIO_MAX31855CS) && PinUsed(GPIO_MAX31855CLK) && PinUsed(GPIO_MAX31855DO)){
switch (function) {
case FUNC_INIT:
MAX31855_Init();
break;
case FUNC_EVERY_SECOND:
MAX31855_GetResult();
break;
case FUNC_JSON_APPEND:
MAX31855_Show(true);
break;
#ifdef USE_WEBSERVER
case FUNC_WEB_SENSOR:
MAX31855_Show(false);
break;
#endif // USE_WEBSERVER
}
}
return result;
}
#endif // USE_MAX31855