otp538u: Initial implementation

This module was tested on the Grove non-contact IR Temperature
Sensor.  The tables included are only valid for a distance of 9cm.

Signed-off-by: Jon Trulson <jtrulson@ics.com>
Signed-off-by: Zion Orent <zorent@ics.com>
Signed-off-by: John Van Drasek <john.r.van.drasek@intel.com>

examples/CMakeLists.txt

@@ -85,6 +85,7 @@ add_executable (cjq4435-example cjq4435.cxx)
 add_executable (adxl335-example adxl335.cxx)
 add_executable (hmtrp-example hmtrp.cxx)
 add_executable (nunchuck-example nunchuck.cxx)
+add_executable (otp538u-example otp538u.cxx)
 
 include_directories (${PROJECT_SOURCE_DIR}/src/hmc5883l)
 include_directories (${PROJECT_SOURCE_DIR}/src/grove)
@@ -155,6 +156,7 @@ include_directories (${PROJECT_SOURCE_DIR}/src/cjq4435)
 include_directories (${PROJECT_SOURCE_DIR}/src/adxl335)
 include_directories (${PROJECT_SOURCE_DIR}/src/hmtrp)
 include_directories (${PROJECT_SOURCE_DIR}/src/nunchuck)
+include_directories (${PROJECT_SOURCE_DIR}/src/otp538u)
 
 target_link_libraries (hmc5883l-example hmc5883l ${CMAKE_THREAD_LIBS_INIT})
 target_link_libraries (groveled-example grove ${CMAKE_THREAD_LIBS_INIT})
@@ -243,3 +245,4 @@ target_link_libraries (cjq4435-example cjq4435 ${CMAKE_THREAD_LIBS_INIT})
 target_link_libraries (adxl335-example adxl335 ${CMAKE_THREAD_LIBS_INIT})
 target_link_libraries (hmtrp-example hmtrp ${CMAKE_THREAD_LIBS_INIT})
 target_link_libraries (nunchuck-example nunchuck ${CMAKE_THREAD_LIBS_INIT})
+target_link_libraries (otp538u-example otp538u ${CMAKE_THREAD_LIBS_INIT})

examples/javascript/otp538u.js

@@ -0,0 +1,64 @@
+/*jslint node:true, vars:true, bitwise:true, unparam:true */
+/*jshint unused:true */
+
+/*
+* Author: Zion Orent <zorent@ics.com>
+* Copyright (c) 2015 Intel Corporation.
+*
+* Permission is hereby granted, free of charge, to any person obtaining
+* a copy of this software and associated documentation files (the
+* "Software"), to deal in the Software without restriction, including
+* without limitation the rights to use, copy, modify, merge, publish,
+* distribute, sublicense, and/or sell copies of the Software, and to
+* permit persons to whom the Software is furnished to do so, subject to
+* the following conditions:
+*
+* The above copyright notice and this permission notice shall be
+* included in all copies or substantial portions of the Software.
+*
+* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+*/
+
+// analog voltage, usually 3.3 or 5.0
+var OTP538U_AREF = 5.0;
+
+var tempIRSensor_lib = require('jsupm_otp538u');
+
+// Instantiate a OTP538U on analog pins A0 and A1
+// A0 is used for the Ambient Temperature and A1 is used for the
+// Object temperature.
+var tempIRSensor_obj = new tempIRSensor_lib.OTP538U(0, 1, OTP538U_AREF);
+
+
+function checkTemp()
+{
+	var outputStr = "Ambient temp: " +
+		roundNum(tempIRSensor_obj.ambientTemperature(), 2) +
+		" C, Object temp: " +
+		roundNum(tempIRSensor_obj.objectTemperature(), 2) +
+		" C";
+	console.log(outputStr);
+}
+
+var myInterval = setInterval(checkTemp, 1000);
+
+function roundNum(num, decimalPlaces)
+{
+	var extraNum = (1 / (Math.pow(10, decimalPlaces) * 1000));
+	return (Math.round((num + extraNum) *
+		(Math.pow(10, decimalPlaces))) / Math.pow(10, decimalPlaces));
+}
+
+// When exiting: clear interval and print message
+process.on('SIGINT', function()
+{
+	clearInterval(myInterval);
+	console.log("Exiting...");
+	process.exit(0);
+});

examples/otp538u.cxx

@@ -0,0 +1,71 @@
+/*
+ * Author: Jon Trulson <jtrulson@ics.com>
+ * Copyright (c) 2014 Intel Corporation.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <unistd.h>
+#include <iostream>
+#include <iomanip>
+#include <signal.h>
+#include "otp538u.h"
+
+using namespace std;
+
+bool shouldRun = true;
+
+// analog voltage, usually 3.3 or 5.0
+#define OTP538U_AREF   5.0
+
+void sig_handler(int signo)
+{
+  if (signo == SIGINT)
+    shouldRun = false;
+}
+
+int main()
+{
+  signal(SIGINT, sig_handler);
+
+//! [Interesting]
+
+  // Instantiate a OTP538U on analog pins A0 and A1
+  // A0 is used for the Ambient Temperature and A1 is used for the
+  // Object tempewrature.
+  upm::OTP538U *temps = new upm::OTP538U(0, 1, OTP538U_AREF);
+  
+  // Output ambient and object temperatures
+  while (shouldRun)
+    {
+      cout << "Ambient temp: " << std::fixed << setprecision(2) 
+           << temps->ambientTemperature() 
+           << " C, Object temp: " << temps->objectTemperature() 
+           << " C" << endl;
+      
+      sleep(1);
+    }
+//! [Interesting]
+
+  cout << "Exiting" << endl;
+
+  delete temps;
+  return 0;
+}

src/otp538u/CMakeLists.txt

@@ -0,0 +1,5 @@
+set (libname "otp538u")
+set (libdescription "upm otp538u IR temperature sensor")
+set (module_src ${libname}.cxx)
+set (module_h ${libname}.h)
+upm_module_init()

src/otp538u/jsupm_otp538u.i

@@ -0,0 +1,8 @@
+%module jsupm_otp538u
+%include "../upm.i"
+
+%{
+    #include "otp538u.h"
+%}
+
+%include "otp538u.h"

src/otp538u/otp538u.cxx

@@ -0,0 +1,189 @@
+/*
+ * Author: Jon Trulson <jtrulson@ics.com>
+ * Copyright (c) 2015 Intel Corporation.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <iostream>
+
+#include "otp538u.h"
+
+#include "thermopile_vt_table.h"
+#include "thermister_rt_table.h"
+
+using namespace upm;
+using namespace std;
+
+OTP538U::OTP538U(int pinA, int pinO, float aref)
+{
+  // this is the internal voltage reference on the Grove IR temp
+  // sensor module
+  m_vref = 2.5;
+
+  // analog reference in use
+  m_aref = aref;
+
+  // This is the value of the output resistor of the Grove IR
+  // temp sensor's SIG2 output (ambient)
+  m_vResistance = 2000000;      // 2M ohms
+
+  // This was the default offset voltage in the seeedstudio code.  You
+  // can adjust as neccessary depending on your calibration.
+  m_offsetVoltage = 0.014;
+
+  // We need around 1mV resolution, so use 12 bit resolution (4096)
+  // with a default aref of 5.0.
+  m_adcResolution = 4096;
+
+  if ( !(m_aioA = mraa_aio_init(pinA)) )
+    {
+      cerr << __FUNCTION__ << ": mraa_aio_init() failed" << endl;
+      return;
+    }
+
+  // enable 12 bit resolution
+  mraa_aio_set_bit(m_aioA, 12);
+
+  if ( !(m_aioO = mraa_aio_init(pinO)) )
+    {
+      cerr << __FUNCTION__ << ": mraa_aio_init() failed" << endl;
+      return;
+    }
+
+  // enable 12 bit resolution
+  mraa_aio_set_bit(m_aioO, 12);
+}
+
+OTP538U::~OTP538U()
+{
+  mraa_aio_close(m_aioA);
+  mraa_aio_close(m_aioO);
+}
+
+float OTP538U::ambientTemperature()
+{
+  const int samples = 5;
+  int val = 0;
+  float temp = 0;
+  float res;
+
+  for (int i=0; i<samples; i++)
+    {
+      val = mraa_aio_read(m_aioA);
+      temp += val;
+      usleep(10000);
+    }
+
+  temp = temp / samples;
+  temp = temp * m_aref / m_adcResolution;
+
+  // compute the resistance of the thermistor
+  res = m_vResistance * temp / (m_vref - temp);
+
+  // look it up in the thermistor (RT) resistence/temperature table
+  int rawslot;
+  int j;
+  for (j=0; j<otp538u_rt_table_max; j++)
+    if (otp538u_rt_table[j] < res)
+      {
+        rawslot = j;
+        break;
+      }
+
+  if (j >= otp538u_rt_table_max)
+    { 
+      cerr << __FUNCTION__ << ": ambient temperature out of range." << endl;
+      return 0;
+    }
+
+  // we need to compensate for the fact that we are supporting
+  // temperature values less than 0 (-20C), so adjust correspondingly
+  // so that we obtain the correct temperature 'slot'.  This will be
+  // our base temperature.
+  int slot = rawslot - 20;
+  
+  // too cold
+  if (slot < 0)
+    {
+      cerr << __FUNCTION__ << ": ambient temperature out of range." << endl;
+      return 0;
+    }
+
+  // now compute the ambient temperature
+  float ambientTemp = slot - 1 +
+    (otp538u_rt_table[rawslot - 1]-res) / (otp538u_rt_table[rawslot - 1] - 
+                                           otp538u_rt_table[rawslot]);
+  
+  return ambientTemp;
+}
+
+float OTP538U::objectTemperature()
+{
+  const int samples = 5;
+  const float reference_vol= 0.5; // what is this value? (from seeedstudio)
+  const float tempIncrement=10;
+  int val = 0;
+  float temp = 0;
+  float ambTemp = ambientTemperature();
+  
+  for (int i=0; i<samples; i++)
+    {
+      val = mraa_aio_read(m_aioO);
+      temp += val;
+      usleep(10000);
+    }
+
+  temp = temp / samples;
+
+  float temp1 = temp * m_aref / m_adcResolution;
+  float sensorVolts = temp1 - (reference_vol + m_offsetVoltage);
+  // cout << "Sensor Voltage: " << sensorVolts << endl;
+
+  // search the VT (voltage/temperature) table to find the object
+  // temperature.
+  int slot;
+  // add +2 to compensate for the -20C and -10C slots below zero
+  int voltOffset = int(ambTemp / 10) + 1 + 2;
+  float voltage = sensorVolts * 10.0;
+  for (slot=0; slot<otp538u_vt_table_max; slot++)		
+    {
+      if ( (voltage > otp538u_vt_table[slot][voltOffset]) &&
+           (voltage < otp538u_vt_table[slot+1][voltOffset]) )
+        {
+          break;
+        }
+    }
+
+  if (slot >= (otp538u_vt_table_max - 1))
+    {
+      cerr << __FUNCTION__ << ": object temperature out of range." << endl;
+      return 0;
+    }
+
+  float objTemp = (float(tempIncrement) * voltage) /
+    ( otp538u_vt_table[slot + 1][voltOffset] - 
+      otp538u_vt_table[slot][voltOffset] );    
+
+  //  cout << "TABLE VALUE [" << slot << "][" <<
+  //    voltOffset << "] = " << otp538u_vt_table[slot][voltOffset] << endl;
+
+  return (ambTemp + objTemp);
+}

src/otp538u/otp538u.h

@@ -0,0 +1,141 @@
+/*
+ * Author: Jon Trulson <jtrulson@ics.com>
+ * Copyright (c) 2015 Intel Corporation.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+#pragma once
+
+#include <string>
+#include <mraa/aio.h>
+
+namespace upm {
+
+  /**
+   * @brief C++ API for the OTP538U IR Temperature Sensor
+   *
+   * UPM module for the OTP538U IR Temperature Sensor
+   *
+   * This module was tested with the Grove IR non-contact temperature
+   * sensor.
+   *
+   * The sensor provides 2 analog outputs - one for the thermistor
+   * that measures ambient temperature, and another for the thermopile
+   * that measures object temperature.
+   *
+   * Much of the code depends on analyzing the SeeedStudio examples
+   * and circuit design.  As a result, there are several 'magic'
+   * numbers that were derived from their circuit design.  By default,
+   * these values will be used.
+   *
+   * The tables used came from the datasheets "538U VT
+   * Table__20_200(v1.3).pdf" and "538RT_table.pdf".
+   *
+   * These tables assume the object to be measured is 9cm (3.54
+   * inches) from the sensor.
+   *
+   * @ingroup grove analog
+   * @defgroup otp538u libupm-otp538u
+   * @snippet otp538u.cxx Interesting
+   */
+  class OTP538U {
+  public:
+    /**
+     * OTP538U sensor constructor
+     *
+     * @param pinA analog pin to use for Ambient temperature
+     * @param pinO analog pin to use for Object temperature
+     * @param aref analog reference voltage, default 5.0
+     */
+    OTP538U(int pinA, int pinO, float aref = 5.0);
+
+    /**
+     * OTP538U Destructor
+     */
+    ~OTP538U();
+
+    /**
+     * Get the ambient temperature in C
+     *
+     * @return the ambient temperature
+     */
+    float ambientTemperature();
+
+    /**
+     * Get the object temperature in C
+     *
+     * @return the object's temperature
+     */
+    float objectTemperature();
+
+    /**
+     * Set the offset voltage
+     *
+     * The Seeedstudio wiki gives an example on calibrating the sensor
+     * and calculating the offset voltage to apply.  Currently, the
+     * default value is set, but you can use the function to set one
+     * of your own.
+     *
+     * @param vOffset the desired offset voltage
+     */
+    void setVoltageOffset(float vOffset) { m_offsetVoltage = vOffset; };
+
+    /**
+     * Set the output resistance value
+     *
+     * The Seeedstudio wiki example uses a value, 2000000 in one of
+     * the equations used to calculate a voltage.  The value is the
+     * resistance of a resistor they use in the output stage of their
+     * SIG2 output.  This was 'decoded' by looking at the eagle files
+     * containing their schematics for this device.
+     *
+     * @param outResistance value of output resistor, default 2M Ohm.
+     */
+    void setOutputResistence(int outResistance) { 
+      m_vResistance = outResistance; };
+
+    /**
+     * Set the voltage reference of the internal seedstudio voltage
+     * regulator on the sensor board.
+     *
+     * The Seeedstudio wiki example uses a value, 2.5 in one of the
+     * equations used to calculate the resistance of the ambient
+     * thermistor.  The value is the voltage of an internal voltage
+     * regulator used in the sensor board.  This was 'decoded' by
+     * looking at the eagle files containing their schematics for this
+     * device.
+     *
+     * @param vref internal sensor voltage reference, default 2.5
+     */
+    void setVRef(float vref) { m_vref = vref; };
+
+
+  private:
+    float m_vref;
+    float m_aref;
+    int m_vResistance;
+    float m_offsetVoltage;
+    int m_adcResolution;
+    mraa_aio_context m_aioA;
+    mraa_aio_context m_aioO;
+  };
+}
+
+

src/otp538u/pyupm_otp538u.i

@@ -0,0 +1,9 @@
+%module pyupm_otp538u
+%include "../upm.i"
+
+%feature("autodoc", "3");
+
+%include "otp538u.h"
+%{
+    #include "otp538u.h"
+%}

src/otp538u/thermister_rt_table.h

@@ -0,0 +1,46 @@
+/*
+ * Author: Jon Trulson <jtrulson@ics.com>
+ * Copyright (c) 2015 Intel Corporation.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+// This table was taken from the 538RT_table.pdf datasheet. It maps
+// resistance values to ambient temperatures starting at -20C and
+// going to 200C in increments of 1C
+
+static const int otp538u_rt_table_max = 121;
+
+static int otp538u_rt_table[otp538u_rt_table_max] = {
+  919730, 869299, 821942, 777454, 735644, 696336, 659365, 624578, 591834,
+  561002, 531958, 504588, 478788, 454457, 431504, 409843, 389394, 370082,
+  351839, 334598, 318300, 302903, 288329, 274533, 261471, 249100, 237381,
+  226276, 215750, 205768, 196300, 187316, 178788, 170691, 163002, 155700,
+  148766, 142183, 135936, 130012, 124400, 119038, 113928, 109059, 104420,
+  100000, 95788, 91775, 87950, 84305, 80830, 77517, 74357, 71342, 68466,
+  65720, 63098, 60595, 58202, 55916, 53730, 51645, 49652, 47746, 45924,
+  44180, 42511, 40912, 39380, 37910, 36500, 35155, 33866, 32631, 31446,
+  30311, 29222, 28177, 27175, 26213, 25290, 24403, 23554, 22738, 21955,
+  21202, 20479, 19783, 19115, 18472, 17854, 17260, 16688, 16138, 15608,
+  15098, 14608, 14135, 13680, 13242, 12819, 12412, 12020, 11642, 11278,
+  10926, 10587, 10260, 9945, 9641, 9347, 9063, 8789, 8525, 8270, 8023,
+  7785, 7555, 7333, 7118, 6911 
+};
+ 

src/otp538u/thermopile_vt_table.h

@@ -0,0 +1,104 @@
+/*
+ * Author: Jon Trulson <jtrulson@ics.com>
+ * Copyright (c) 2015 Intel Corporation.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+// This table was taken from the 538U VT Table__20_200(v1.3).pdf
+// datasheet, but the 25C column has been removed for consistency.
+
+static const int otp538u_vt_table_max = 23;
+
+// Thermister temperature (C)
+// { -20 -10 0 10 20 30 40 50 60 70 80 90 100 }
+
+static float otp538u_vt_table[otp538u_vt_table_max][13] = {
+                                                  // object temp (C)  
+  {0.000, -0.246, -0.523, -0.832, -1.177, -1.559, // -20C 
+   -1.981, -2.446, -2.957, -3.516, -4.126, -4.791, -5.513},
+  
+  {0.243, 0.000, -0.274, -0.580, -0.922, -1.301, // -10
+   -1.721, -2.183, -2.691, -3.247, -3.854, -4.516, -5.236},
+  
+  {0.511, 0.271, 0.000, -0.303, -0.642, -1.018, // 0
+   -1.434, -1.894, -2.398, -2.951, -3.556, -4.215, -4.931},
+  
+  {0.804, 0.567, 0.300, 0.000, -0.335, -0.708, // 10
+   -1.121, -1.577, -2.078, -2.628, -3.229, -3.884, -4.597},
+  
+  {1.125, 0.891, 0.628, 0.331, 0.000, -0.369, // 20
+   -0.778, -1.230, -1.728, -2.274, -2.871, -3.523, -4.232},
+  
+  {1.474, 1.244, 0.985, 0.692, 0.365, 0.000, // 30
+   -0.405, -0.853, -1.347, -1.889, -2.482, -3.130, -3.835},
+  
+  {1.852, 1.628, 1.372, 1.084, 0.761, 0.401, // 40
+   0.000, -0.444, -0.933, -1.470, -2.059, -2.702, -3.403},
+  
+  {2.263, 2.043, 1.792, 1.509, 1.191, 0.835, // 50
+   0.439, 0.000, -0.484, -1.017, -1.601, -2.240, -2.936},
+  
+  {2.706, 2.491, 2.246, 1.968, 1.655, 1.304, // 60
+   0.913, 0.479, 0.000, -0.528, -1.107, -1.740, -2.431},
+  
+  {3.184, 2.975, 2.735, 2.462, 2.155, 1.809, // 70
+   1.424, 0.996, 0.522, 0.000, -0.573, -1.201, -1.887},
+  
+  {3.698, 3.495, 3.261, 2.994, 2.692, 2.353, // 80
+   1.974, 1.552, 1.084, 0.568, 0.000, -0.622, -1.301},
+  
+  {4.250, 4.053, 3.825, 3.565, 3.270, 2.937, // 90
+   2.564, 2.148, 1.687, 1.177, 0.616, 0.000, -0.673},
+  
+  {4.841, 4.651, 4.430, 4.177, 3.888, 3.562, // 100
+   3.196, 2.787, 2.332, 1.829, 1.275, 0.666, 0.000},
+  
+  {5.473, 5.290, 5.076, 4.830, 4.549, 4.231, // 110
+   3.872, 3.470, 3.023, 2.527, 1.980, 1.379, 0.720},
+  
+  {6.147, 5.972, 5.767, 5.528, 5.255, 4.944, // 120
+   4.593, 4.199, 3.760, 3.272, 2.733, 2.139, 1.488},
+  
+  {6.866, 6.699, 6.502, 6.272, 6.007, 5.705, // 130
+   5.362, 4.976, 4.545, 4.066, 3.535, 2.950, 2.307},
+  
+  {7.631, 7.473, 7.285, 7.064, 6.808, 6.514, // 140
+   6.180, 5.803, 5.381, 4.910, 4.388, 3.812, 3.178},
+  
+  {8.444, 8.295, 8.116, 7.905, 7.658, 7.373, // 150
+   7.049, 6.682, 6.269, 5.807, 5.295, 4.728, 4.103},
+  
+  {9.306, 9.167, 8.998, 8.796, 8.560, 8.285, // 160
+   7.971, 7.613, 7.211, 6.759, 6.257, 5.700, 5.085},
+  
+  {10.219, 10.091, 9.933, 9.741, 9.515, 9.251, // 170
+   8.947, 8.601, 8.208, 7.768, 7.276, 6.729, 6.125},
+  
+  {11.185, 11.068, 10.921, 10.741, 10.526, 10.274, // 180
+   9.981, 9.645, 9.264, 8.835, 8.354, 7.818, 7.226},
+  
+  {12.206, 12.101, 11.966, 11.798, 11.595, 11.354, // 190
+   11.073, 10.749, 10.380, 9.962, 9.493, 8.969, 8.388},
+  
+  {13.284, 13.191, 13.068, 12.913, 12.722, 12.494, // 200
+   12.225, 11.914, 11.557, 11.152, 10.695, 10.184, 9.616}
+};
+