Merge pull request #12 from RobTillaart/develop

fix #8 support hardware SPI + example

MAX31855.cpp

@@ -1,13 +1,14 @@
 //
 //    FILE: MAX31855.cpp
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.2.2
+// VERSION: 0.2.3
 // PURPOSE: Arduino library for MAX31855 chip for K type thermocouple
 //    DATE: 2014-01-01
 //     URL: https://github.com/RobTillaart/MAX31855_RT
 //
 // HISTORY:
 //
+// 0.2.3  2020-08-30 fix #8 support hardware SPI + example
 // 0.2.2  2020-08-30 fix#9 + fix failing examples + minor refactor
 // 0.2.1  2020-08-26 read rawData and STATUS_NO_COMMUNICATION recognition (thanks to FabioBrondo)
 // 0.2.0  2020-06-20 #pragma once; major refactor; removed pre 1.0 support; fix offset
@@ -28,11 +29,25 @@
 #include "MAX31855.h"
 
 
+MAX31855::MAX31855(const uint8_t cs)
+{
+  _cs = cs;
+  _hwSPI = true;
+
+  _offset = 0;
+  _SC = K_TC;
+  _status = STATUS_NOREAD;
+  _temperature = -999;
+  _internal = -999;
+}
+
 MAX31855::MAX31855(const uint8_t sclk, const uint8_t cs, const uint8_t miso)
 {
   _sclk = sclk;
   _cs = cs;
   _miso = miso;
+  _hwSPI = false;
+
   _offset = 0;
   _SC = K_TC;
   _status = STATUS_NOREAD;
@@ -44,9 +59,16 @@ void MAX31855::begin()
 {
   pinMode(_cs, OUTPUT);
   digitalWrite(_cs, HIGH);
-
-  pinMode(_sclk, OUTPUT);
-  pinMode(_miso, INPUT);
+  if (_hwSPI)
+  {
+    SPI.begin();
+    delay(1);
+  }
+  else
+  {
+    pinMode(_sclk, OUTPUT);
+    pinMode(_miso, INPUT);
+  }
 }
 
 
@@ -115,21 +137,30 @@ uint8_t MAX31855::read()
 uint32_t MAX31855::_read(void)
 {
   _rawData = 0;
-
   digitalWrite(_cs, LOW);
-
-  for (int8_t i = 31; i >= 0; i--)
+  if (_hwSPI)
   {
-    _rawData <<= 1;
-    digitalWrite(_sclk, LOW);
-    // delayMicroseconds(1);  // DUE
-    if ( digitalRead(_miso) ) _rawData++;
-    digitalWrite(_sclk, HIGH);
-    // delayMicroseconds(1);  // DUE
+    SPI.beginTransaction(SPISettings(16000000, MSBFIRST, SPI_MODE0));
+    for (uint8_t i = 0; i < 4; i++)
+    {
+      _rawData <<= 8;
+      _rawData += SPI.transfer(0);
+    }
+    SPI.endTransaction();
+  }
+  else
+  {
+    for (int8_t i = 31; i >= 0; i--)
+    {
+      _rawData <<= 1;
+      digitalWrite(_sclk, LOW);
+      // delayMicroseconds(1);  // DUE
+      if ( digitalRead(_miso) ) _rawData++;
+      digitalWrite(_sclk, HIGH);
+      // delayMicroseconds(1);  // DUE
+    }
   }
-
   digitalWrite(_cs, HIGH);
-
   return _rawData;
 }
 

MAX31855.h

@@ -2,7 +2,7 @@
 //
 //    FILE: MAX31855.h
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.2.2
+// VERSION: 0.2.3
 // PURPOSE: Arduino library for MAX31855 chip for K type thermocouple
 //    DATE: 2014-01-01
 //     URL: https://github.com/RobTillaart/MAX31855_RT
@@ -20,8 +20,9 @@
 //     +---------+
 
 #include "Arduino.h"
+#include "SPI.h"
 
-#define MAX31855_VERSION           "0.2.2"
+#define MAX31855_VERSION           "0.2.3"
 
 
 // STATE constants returnd by read()
@@ -58,7 +59,9 @@
 class MAX31855
 {
 public:
-
+  // HW SPI
+  MAX31855(uint8_t CS);
+  // SW SPI
   MAX31855(uint8_t SCLK, uint8_t CS, uint8_t MISO);
   void begin();
 
@@ -97,6 +100,7 @@ class MAX31855
   float    _SC;
   uint32_t _lastRead;
   uint32_t _rawData;
+  bool     _hwSPI;
 
   uint8_t  _sclk;
   uint8_t  _miso;

README.md

@@ -28,6 +28,28 @@ Library tested with breakout board
 
 ```
 
+## Hardware SPI vs software SPI
+
+Default pin connections (ESP32 has more options)
+
+ | HW SPI   |  UNO  |  ESP32  |
+ |:---------|:-----:|:-------:|
+ | CLOCKPIN |   13  |   18    |
+ | MISO     |   12  |   19    |
+ | MOSI     |   11  |   23    |
+
+Performance read() function, timing in us.
+
+| mode | clock | timng UNO |
+|:----|----:|----:|
+| HWSPI | 16000000 | ~68  |
+| HWSPI |  4000000 | ~72  |
+| HWSPI |  1000000 | ~100 |
+| HWSPI |   500000 | ~128 |
+| SWSPI | bitbang  | ~500 |
+
+
+
 ## Interface
 
 To make a temperature reading call **tc.read()**.

examples/max31855_hwSPI/max31855_hwSPI.ino

@@ -0,0 +1,68 @@
+//
+//    FILE: max31855_hw_SPI.ino
+//  AUTHOR: Rob Tillaart
+// VERSION: 0.1.0
+// PURPOSE: thermocouple lib demo application
+//    DATE: 2020-08-30
+//     URL: https://github.com/RobTillaart/MAX31855_RT
+//
+
+#include "MAX31855.h"
+
+//
+// | HW SPI   |  UNO  |  ESP32  |
+// |:---------|:-----:|:-------:|
+// | CLOCKPIN |   13  |   18    |
+// | MISO     |   12  |   19    |
+// | MOSI     |   11  |   23    |
+
+// read()            timing UNO 
+// HWSPI  16000000   ~68  us
+// HWSPI   4000000   ~72  us
+// HWSPI   1000000   ~100 us
+// HWSPI    500000   ~128 us
+// SWSPI  bitbang    ~500 us
+
+const int csPin = 6;
+
+uint32_t start, stop;
+
+MAX31855 tc(csPin);
+// MAX31855 tc(13, 6, 12);  // sw SPI
+
+void setup()
+{
+  Serial.begin(115200);
+  Serial.print("Start max31855_demo0: ");
+  Serial.println(MAX31855_VERSION);
+  Serial.println();
+
+  tc.begin();
+}
+
+void loop()
+{
+  start = micros();
+  int status = tc.read();
+  stop = micros();
+
+  Serial.println();
+  Serial.print("time:\t\t");
+  Serial.println(stop - start);
+
+  Serial.print("stat:\t\t");
+  Serial.println(status);
+
+  uint32_t raw = tc.getRawData();
+  Serial.print("raw:\t\t");
+  Serial.println(raw, BIN);
+
+  float internal = tc.getInternal();
+  Serial.print("internal:\t");
+  Serial.println(internal);
+
+  float temp = tc.getTemperature();
+  Serial.print("temperature:\t");
+  Serial.println(temp);
+  delay(1000);
+}

library.json

@@ -15,7 +15,7 @@
     "type": "git",
     "url": "https://github.com/RobTillaart/MAX31855_RT"
   },
-  "version":"0.2.2",
+  "version":"0.2.3",
   "frameworks": "arduino",
   "platforms": "*"
 }

library.properties

@@ -1,5 +1,5 @@
 name=MAX31855_RT
-version=0.2.2
+version=0.2.3
 author=Rob Tillaart <[email protected]>
 maintainer=Rob Tillaart <[email protected]>
 sentence=Arduino library for MAX31855 chip for K type thermocouple.