2020年11月 – ページ 2

測温抵抗体に続き今度は熱電対をMAX31856を使って試して見た。

MAX31856は様々なタイプの熱電対に対応し計測と同時にフォールト検出も行ってくれたりしてとても便利なチップだ。

実際に計測してみると測温抵抗体に比べ計測値の小数点以下第二位以下に不安定性さを感じてしまうが熱応答性が良いため目的に応じて使い分けするのが良さそうだ。

ちなみにチップ内部の冷接点補償温度センサーの測定値自体にパラツキがあるので外付けの冷接点補償温度センサーとの組み合わせでより安定した高精度な測定が出来きるのかもしれない。

Adafruit Universal Thermocouple Amplifier MAX31856 Breakout

【概要】

void cj_offset(int8_t temp)

1	void cj_offset(int8_t temp)

内蔵冷接点補償温度センサーのオフセット温度(x16)を設定する。設定範囲は、-8.00℃ から +7.96℃まで。

void cj_temperature(int16_t temp)

1	void cj_temperature(int16_t temp)

冷接点補償温度(x256)を設定する。設定範囲は、-64.000℃ から +128.008℃ まで。MAX31856_CJ_DISABLE時にのみ有効。

int16_t cj_temperature(void)

1	int16_t cj_temperature(void)

冷接点補償温度(x256)を取得する。取得範囲は、-64.000℃ から +128.008℃ まで。

void cj_threshold(int8_t low = -64, int8_t high = 127)

1	void cj_threshold(int8_t low = -64, int8_t high = 127)

冷接点補償温度の制限値(x1)を設定する。設定範囲は、-64℃ から +127℃まで。範囲外になるとフォールトが発生する。

void threshold(int16_t low = -32768, int16_t high = 32767)

1	void threshold(int16_t low = -32768, int16_t high = 32767)

熱電対センサーの温度制限値(x16)を設定する。設定範囲は、-2048℃ から +2047.96℃まで。範囲外になるとフォールトが発生する。

void fault_mask(MAX31856_MASK mask)

1	void fault_mask(MAX31856_MASK mask)

フォールト・ピン出力のマスクを設定する。※フォールト・ステータスには影響しない。

MAX31856_MASK fault_mask(void)

1	MAX31856_MASK fault_mask(void)

フォールト・ピン出力のマスクを取得する。

bool oneshot(void)

1	bool oneshot(void)

ワンショット変換を実行する。戻り値がtrueならtemperatute()で温度或いは電圧が取得でき、falseならstatus()でフォールトの原因を調べることが出来る。関数内部で変換完了待ちを行う。

void start(void)

1	void start(void)

連続変換モードを開始する。

void stop(void)

1	void stop(void)

連続変換モードを停止する。

int16_t temperature(void)

1	int16_t temperature(void)

対応する熱電対タイプでは計測した温度(x256)を返し、電圧測定モード(MAX31856_TCTYPE_x8 or MAX31856_TCTYPE_x32)では計測した電圧(x8 or x32)uVを返す。

MAX31856_SR status(void)

1	MAX31856_SR status(void)

フォールト・ステータスを取得する。

MAX31856_STATUS handle(void)

1	MAX31856_STATUS handle(void)

連続変換モードを処理する。戻り値は次の通り。
MAX31856_STATUS_IDLE … 停止中。
MAX31856_STATUS_BUSY … 計測中
MAX31856_STATUS_READY … 計測完了。temperature()で温度を取得できる。
MAX31856_STATUS_FAULT … フォールト発生。status()でフォールト・ステータスを取得できる。

【サンプル・スケッチ】

#include "max31856.h"
#include "spibus.h"

#define CS_PIN 10  // A10

#define SPIBUS SPIBUS<CS_PIN, MAX31856_SPI_CLOCK>

SPIBUS spi;
MAX31856<SPIBUS, spi, -1, MAX31856_TCTYPE_K, MAX31856_FILTER_60HZ, MAX31856_AVGSEL_1, MAX31856_OCFAULT_DISABLE> thc;

void setup()
{
  uint32_t t = millis();
  while((millis() - t < 5000) && !Serial)
    continue;
  spi.begin();
  thc.start();
}

void loop()
{
  MAX31856_SR fault;
  switch (thc.handle())
  {
    case MAX31856_STATUS_READY:
      Serial.print("temp = ");
      Serial.println(thc.temperature() / 256.0);
      delay(500);
      break;
    case MAX31856_STATUS_FAULT:
      fault = thc.status();
      Serial.print("fault = 0x");
      if (fault.reg < 10)
        Serial.print("0");
      Serial.println(fault.reg, HEX);
      delay(500);
      break;
    default:
      break;
  }
}

#include "max31856.h"

#include "spibus.h"

#define CS_PIN 10 // A10

#define SPIBUS SPIBUS<CS_PIN, MAX31856_SPI_CLOCK>

SPIBUS spi;

MAX31856<SPIBUS, spi, -1, MAX31856_TCTYPE_K, MAX31856_FILTER_60HZ, MAX31856_AVGSEL_1, MAX31856_OCFAULT_DISABLE> thc;

void setup()

{

uint32_t t = millis();

while((millis() - t < 5000) && !Serial)

continue;

spi.begin();

thc.start();

}

void loop()

{

MAX31856_SR fault;

switch (thc.handle())

{

case MAX31856_STATUS_READY:

Serial.print("temp = ");

Serial.println(thc.temperature() / 256.0);

delay(500);

break;

case MAX31856_STATUS_FAULT:

fault = thc.status();

Serial.print("fault = 0x");

if (fault.reg < 10)

Serial.print("0");

Serial.println(fault.reg, HEX);

delay(500);

break;

default:

break;

}

【更新情報】
2020-11-21
FAULT-MASKの仕様を勘違いしていた。FAULT-MASKを設定／取得する関数を追加。

2020-11-12
DRDYピンを利用できるよう改良してみた。フォールト検出を行う連続変換は１６回毎にフォールト検出が行われるが、そのタイミングを知ることができないため毎回フォールト検出時間を含めた時間を待つしかないが、DRDYピンを使うことで無駄な待ち時間を削除できる。と言ってもそこまで変換時間に拘る必要性があるかどうかは微妙な気もするが．．．

【ライブラリ】

/*
  max31856.h - Thermocouple Sensor Library for MAX31856

  Copyright (c) 2020 Sasapea's Lab. All right reserved.

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library 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
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General
  Public License along with this library; if not, write to the
  Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  Boston, MA  02111-1307  USA
*/
#ifndef __MAX31856_H
#define __MAX31856_H

#include <stdint.h>
#include <stdbool.h>

#define MAX31856_SPI_CLOCK 5000000

typedef enum : uint8_t
{
  MAX31856_REGISTER_CR0,
  MAX31856_REGISTER_CR1,
  MAX31856_REGISTER_MASK,
  MAX31856_REGISTER_CJHF,
  MAX31856_REGISTER_CJLF,
  MAX31856_REGISTER_LTHFTH,
  MAX31856_REGISTER_LTHFTL,
  MAX31856_REGISTER_LTLFTH,
  MAX31856_REGISTER_LTLFTL,
  MAX31856_REGISTER_CJTO,
  MAX31856_REGISTER_CJTH,
  MAX31856_REGISTER_CJTL,
  MAX31856_REGISTER_LTCBH,
  MAX31856_REGISTER_LTCBM,
  MAX31856_REGISTER_LTCBL,
  MAX31856_REGISTER_SR,
} MAX31856_REGISTER;

#define MAX31856_REGISTER_W 0x80

typedef enum : uint8_t
{
  MAX31856_FILTER_60HZ,
  MAX31856_FILTER_50HZ,
} MAX31856_FILTER;

typedef enum : uint8_t
{
  MAX31856_CJ_ENABLE,
  MAX31856_CJ_DISABLE,
} MAX31856_CJ;

typedef enum : uint8_t
{
  MAX31856_OCFAULT_DISABLE,  //  disable
  MAX31856_OCFAULT_LT_5K,    //  Rs < 5K
  MAX31856_OCFAULT_GT_5K_S,  //  40K > Rs > 5K (time constant < 2ms)
  MAX31856_OCFAULT_GT_5K_L,  //  40K > Rs > 5K (time constant > 2ms)
} MAX31856_OCFAULT;

typedef enum : uint8_t
{
  MAX31856_TCTYPE_B,   // B type
  MAX31856_TCTYPE_E,   // E type
  MAX31856_TCTYPE_J,   // J type
  MAX31856_TCTYPE_K,   // K type (default)
  MAX31856_TCTYPE_N,   // N type
  MAX31856_TCTYPE_R,   // R type
  MAX31856_TCTYPE_S,   // S type
  MAX31856_TCTYPE_T,   // T type
  MAX31856_TCTYPE_x8  = 0b1000, // voltage mode, amplifire  x8, code =  8 x 1.6 x 2e17 x VIN
  MAX31856_TCTYPE_x32 = 0b1100, // voltage mode, amplifire x32, code = 32 x 1.6 x 2e17 x VIN
} MAX31856_TCTYPE;

typedef enum : uint8_t
{
  MAX31856_AVGSEL_1,  //  1 sample (default)
  MAX31856_AVGSEL_2,  //  2 sample
  MAX31856_AVGSEL_4,  //  4 sample
  MAX31856_AVGSEL_8,  //  8 sample
  MAX31856_AVGSEL_16, // 16 sample
} MAX31856_AVGSEL;

typedef union
{
  struct
  {
    uint8_t TCTYPE:4;
    uint8_t AVGSEL:3;
    uint8_t RESERVED:1;
    uint8_t FILTER:1;
    uint8_t FAULTCLR:1;
    uint8_t FAULT:1;
    uint8_t CJ:1;
    uint8_t OCFAULT:2;
    uint8_t ONESHOT:1;
    uint8_t CMODE:1;
  } bit;
  uint16_t reg;
} MAX31856_CR;

typedef union
{
  struct
  {
    uint8_t OPEN:1;
    uint8_t OVUV:1;
    uint8_t TCLOW:1;
    uint8_t TCHIGH:1;
    uint8_t CJLOW:1;
    uint8_t CJHIGH:1;
    uint8_t RESERVED:2;
  } bit;
  uint8_t reg;
} MAX31856_MASK;

typedef union
{
  struct
  {
    uint8_t OPEN:1;
    uint8_t OVUV:1;
    uint8_t TCLOW:1;
    uint8_t TCHIGH:1;
    uint8_t CJLOW:1;
    uint8_t CJHIGH:1;
    uint8_t TCRANGE:1;
    uint8_t CJRANGE:1;
  } bit;
  uint8_t reg;
} MAX31856_SR;

typedef enum : uint8_t
{
  MAX31856_STATUS_IDLE,
  MAX31856_STATUS_BUSY,
  MAX31856_STATUS_READY,
  MAX31856_STATUS_FAULT,
} MAX31856_STATUS;

// conversion time
#define MAX31856_TCONV_SINGLE_50HZ             185000UL // TYP: 16900 MAX:185000
#define MAX31856_TCONV_SINGLE_60HZ             155000UL // TYP: 14300 MAX:155000
#define MAX31856_TCONV_CONTINUOUS_50HZ         110000UL // TYP: 98000 MAX:110000
#define MAX31856_TCONV_CONTINUOUS_60HZ          90000UL // TYP: 82000 MAX: 90000
#define MAX31856_TCONV_CJ(c)                   ((c) ? 25000UL : 0UL)
#define MAX31856_TCONV_SINGLE_AVGSEL(f, n) \
  ((f) == MAX31856_FILTER_60HZ ? (33333UL * ((1 << (n)) - 1)) : (40000UL * ((1 << (n)) - 1)))
#define MAX31856_TCONV_CONTINUOUS_AVGSEL(f, n) \
  ((f) == MAX31856_FILTER_60HZ ? (16666UL * ((1 << (n)) - 1)) : (20000UL * ((1 << (n)) - 1)))
#define MAX31856_TCONV_SINGLE(f, n, c) \
  (((f) == MAX31856_FILTER_60HZ ? MAX31856_TCONV_SINGLE_60HZ : MAX31856_TCONV_SINGLE_50HZ) \
  - MAX31856_TCONV_CJ(c) + MAX31856_TCONV_SINGLE_AVGSEL(f, n))
#define MAX31856_TCONV_CONTINUOUS(f, n, c) \
  (((f) == MAX31856_FILTER_60HZ ? MAX31856_TCONV_CONTINUOUS_60HZ : MAX31856_TCONV_CONTINUOUS_50HZ) \
  - MAX31856_TCONV_CJ(c) + MAX31856_TCONV_CONTINUOUS_AVGSEL(f, n))

// fault test time
#define MAX31856_TTEST_OCFAULT_CJ_ENABLE_1      15000UL // TYP: 13300 MAX: 15000
#define MAX31856_TTEST_OCFAULT_CJ_ENABLE_2      37000UL // TYP: 33400 MAX: 37000
#define MAX31856_TTEST_OCFAULT_CJ_ENABLE_3     125000UL // TYP:113400 MAX:125000
#define MAX31856_TTEST_OCFAULT_CJ_ENABLE(o) \
  ((o) == MAX31856_OCFAULT_LT_5K   ? MAX31856_TTEST_OCFAULT_CJ_ENABLE_1 : \
  ((o) == MAX31856_OCFAULT_GT_5K_S ? MAX31856_TTEST_OCFAULT_CJ_ENABLE_2 : \
  ((o) == MAX31856_OCFAULT_GT_5K_L ? MAX31856_TTEST_OCFAULT_CJ_ENABLE_3 : \
  0UL)))
#define MAX31856_TTEST_OCFAULT_CJ_DISABLE_1     44000UL // TYP: 40000 MAX: 44000
#define MAX31856_TTEST_OCFAULT_CJ_DISABLE_2     66000UL // TYP: 60000 MAX: 66000
#define MAX31856_TTEST_OCFAULT_CJ_DISABLE_3    154000UL // TYP:140000 MAX:154000
#define MAX31856_TTEST_OCFAULT_CJ_DISABLE(o) \
  ((o) == MAX31856_OCFAULT_LT_5K   ? MAX31856_TTEST_OCFAULT_CJ_DISABLE_1 : \
  ((o) == MAX31856_OCFAULT_GT_5K_S ? MAX31856_TTEST_OCFAULT_CJ_DISABLE_2 : \
  ((o) == MAX31856_OCFAULT_GT_5K_L ? MAX31856_TTEST_OCFAULT_CJ_DISABLE_3 : \
  0UL)))
#define MAX31856_TTEST_OCFAULT(c, o) \
  ((c) ? MAX31856_TTEST_OCFAULT_CJ_DISABLE(o) : MAX31856_TTEST_OCFAULT_CJ_ENABLE(o))

template
<
  typename SPIBUS_T,
  SPIBUS_T &SPIBUS,
  int DRDY = -1,
  MAX31856_TCTYPE  TCTYPE  = MAX31856_TCTYPE_K,
  MAX31856_FILTER  FILTER  = MAX31856_FILTER_60HZ,
  MAX31856_AVGSEL  AVGSEL  = MAX31856_AVGSEL_1,
  MAX31856_OCFAULT OCFAULT = MAX31856_OCFAULT_LT_5K,
  MAX31856_CJ      CJ      = MAX31856_CJ_ENABLE
>
class MAX31856
{
  private:

    MAX31856_CR   _cr;
    MAX31856_SR   _sr;
    MAX31856_MASK _mask;
    int32_t       _temp;
    uint32_t      _start;
    uint32_t      _tconv;
    uint8_t       _ready;

    void write(MAX31856_REGISTER reg, uint8_t value)
    {
      uint8_t buf[] = {(uint8_t)(reg | MAX31856_REGISTER_W), value};
      SPIBUS.write(buf, sizeof(buf));
    }

    void write16(MAX31856_REGISTER reg, uint16_t value)
    {
      uint8_t buf[] = {(uint8_t)(reg | MAX31856_REGISTER_W), (uint8_t)(value >> 8), (uint8_t)value};
      SPIBUS.write(buf, sizeof(buf));
    }

    void write32(MAX31856_REGISTER reg, uint32_t value)
    {
      uint8_t buf[] = {(uint8_t)(reg | MAX31856_REGISTER_W), (uint8_t)(value >> 24), (uint8_t)(value >> 16), (uint8_t)(value >> 8), (uint8_t)value};
      SPIBUS.write(buf, sizeof(buf));
    }

    uint8_t read(MAX31856_REGISTER reg)
    {
      uint8_t buf[] = {reg};
      SPIBUS.writeAndRead(buf, 1, buf, sizeof(buf));
      return buf[0];
    }

    uint16_t read16(MAX31856_REGISTER reg)
    {
      uint8_t buf[2] = {reg};
      SPIBUS.writeAndRead(buf, 1, buf, sizeof(buf));
      return ((uint16_t)buf[0] << 8) | buf[1];
    }

    uint32_t read32(MAX31856_REGISTER reg)
    {
      uint8_t buf[4] = {reg};
      SPIBUS.writeAndRead(buf, 1, buf, sizeof(buf));
      return ((uint32_t)buf[0] << 24) | ((uint32_t)buf[1] << 16) | ((uint16_t)buf[2] << 8) | buf[3];
    }

    void clear(void)
    {
      _cr.bit.FAULTCLR = 1;
      write16(MAX31856_REGISTER_CR0, _cr.reg);
      _cr.bit.FAULTCLR = 0;
    }

    bool readLT(void)
    {
      int32_t lt = (int32_t)read32(MAX31856_REGISTER_LTCBH);
      _sr.reg = (uint8_t)lt;
      if (TCTYPE & MAX31856_TCTYPE_x8)
        _sr.bit.TCRANGE = 0;
      if (_sr.reg)
      {
        clear();
        return false;
      }
      if (TCTYPE & MAX31856_TCTYPE_x8)
        _temp = ((int64_t)(lt >> 13) * 10000000) >> (4 + 17); // code = 1.6 x 2e17 x VIN
      else
        _temp = (lt >> 12) & ~1;
      return true;
    }

  public:

    MAX31856(void)
    : _temp(0)
    , _start(0)
    , _tconv(0)
    , _ready(0)
    {
      _sr.reg = 0;
      _cr.reg = 0;
      _cr.bit.FILTER  = FILTER;
      _cr.bit.FAULT   = 1; // interrupt mode
      _cr.bit.CJ      = CJ;
      _cr.bit.OCFAULT = OCFAULT;
      _cr.bit.TCTYPE  = TCTYPE;
      _cr.bit.AVGSEL  = AVGSEL;
      _mask.reg = 0xFF;
    }

    virtual ~MAX31856(void)
    {
    }

    void cj_offset(int8_t temp)
    {
      write(MAX31856_REGISTER_CJTO, (uint8_t)temp);
    }

    void cj_temperature(int16_t temp)
    {
      if (temp < (-64 << 8))
        temp = (-64 << 8);
      write16(MAX31856_REGISTER_CJTH, (uint16_t)temp);
    }

    int16_t cj_temperature(void)
    {
      return (int16_t)read16(MAX31856_REGISTER_CJTH);
    }

    void cj_threshold(int8_t low = -64, int8_t high = 127)
    {
      if (low < -64)
        low = -64;
      if (high < -64)
        high = -64;
      write16(MAX31856_REGISTER_CJHF, ((uint16_t)high << 8) | low);
    }

    void threshold(int16_t low = -32768, int16_t high = 32767)
    {
      write32(MAX31856_REGISTER_LTHFTH, ((uint32_t)high << 16) | low);
    }

    void fault_mask(MAX31856_MASK mask)
    {
      write(MAX31856_REGISTER_MASK, _mask = mask);
    }

    MAX31856_MASK fault_mask(void)
    {
      return _mask;
    }

    bool oneshot(void)
    {
      // start one short
      _tconv = 0;
      _cr.bit.CMODE   = 0;
      _cr.bit.ONESHOT = 1;
      write16(MAX31856_REGISTER_CR0, _cr.reg);
      _cr.bit.ONESHOT = 0;
      if (DRDY >= 0)
      {
        uint32_t t = micros();
        uint8_t  d = digitalRead(DRDY);
        do
        {
          // detect falling edge
          if (d != digitalRead(DRDY))
          {
            d = !d;
            if (!d)
              break;
          }
          yield();
        }
        while (micros() - t < MAX31856_TCONV_SINGLE(FILTER, AVGSEL, CJ) + MAX31856_TTEST_OCFAULT(CJ, OCFAULT));
      }
      else
      {
#if defined(__GNUC__)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Woverflow"
#endif
        delayMicroseconds(MAX31856_TCONV_SINGLE(FILTER, AVGSEL, CJ) + MAX31856_TTEST_OCFAULT(CJ, OCFAULT));
#if defined(__GNUC__)
#pragma GCC diagnostic pop
#endif
      }
      return readLT();
    }

    void start(void)
    {
      // start continuous mode
      _ready = 0;
      _tconv = MAX31856_TCONV_SINGLE(FILTER, AVGSEL, CJ) + MAX31856_TTEST_OCFAULT(CJ, OCFAULT);
      _cr.bit.CMODE = 1;
      write16(MAX31856_REGISTER_CR0, _cr.reg);
      _start = micros();
      if (DRDY >= 0)
        _ready = digitalRead(DRDY);
    }

    void stop(void)
    {
      _tconv = 0;
      _cr.bit.CMODE = 0;
      write16(MAX31856_REGISTER_CR0, _cr.reg);
    }

    int32_t temperature(void)
    {
      return _temp;
    }

    MAX31856_SR status(void)
    {
      return _sr;
    }

    MAX31856_STATUS handle(void)
    {
      if (_tconv == 0)
        return MAX31856_STATUS_IDLE;
      if (micros() - _start >= _tconv)
        _start += _tconv;
      else
      {
        if (DRDY < 0)
          return MAX31856_STATUS_BUSY;
        // detect falling edge
        if (_ready == digitalRead(DRDY))
          return MAX31856_STATUS_BUSY;
        _ready = !_ready;
        if (_ready)
          return MAX31856_STATUS_BUSY;
        _start = micros();
      }
      _tconv = MAX31856_TCONV_CONTINUOUS(FILTER, AVGSEL, CJ) + MAX31856_TTEST_OCFAULT(CJ, OCFAULT);
      return readLT() ? MAX31856_STATUS_READY : MAX31856_STATUS_FAULT;
    }
};

#endif

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max31856.h - Thermocouple Sensor Library for MAX31856

This library is free software; you can redistribute it and/or

modify it under the terms of the GNU Lesser General Public

License as published by the Free Software Foundation; either

version 2.1 of the License, or (at your option) any later version.

This library 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

Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General

Public License along with this library; if not, write to the

Free Software Foundation, Inc., 59 Temple Place, Suite 330,

Boston, MA 02111-1307 USA

#ifndef __MAX31856_H

#define __MAX31856_H

#include <stdint.h>

#include <stdbool.h>

#define MAX31856_SPI_CLOCK 5000000

typedef enum : uint8_t

{

MAX31856_REGISTER_CR0,

MAX31856_REGISTER_CR1,

MAX31856_REGISTER_MASK,

MAX31856_REGISTER_CJHF,

MAX31856_REGISTER_CJLF,

MAX31856_REGISTER_LTHFTH,

MAX31856_REGISTER_LTHFTL,

MAX31856_REGISTER_LTLFTH,

MAX31856_REGISTER_LTLFTL,

MAX31856_REGISTER_CJTO,

MAX31856_REGISTER_CJTH,

MAX31856_REGISTER_CJTL,

MAX31856_REGISTER_LTCBH,

MAX31856_REGISTER_LTCBM,

MAX31856_REGISTER_LTCBL,

MAX31856_REGISTER_SR,

} MAX31856_REGISTER;

#define MAX31856_REGISTER_W 0x80

typedef enum : uint8_t

{

MAX31856_FILTER_60HZ,

MAX31856_FILTER_50HZ,

} MAX31856_FILTER;

typedef enum : uint8_t

{

MAX31856_CJ_ENABLE,

MAX31856_CJ_DISABLE,

} MAX31856_CJ;

typedef enum : uint8_t

{

MAX31856_OCFAULT_DISABLE, // disable

MAX31856_OCFAULT_LT_5K, // Rs < 5K

MAX31856_OCFAULT_GT_5K_S, // 40K > Rs > 5K (time constant < 2ms)

MAX31856_OCFAULT_GT_5K_L, // 40K > Rs > 5K (time constant > 2ms)

} MAX31856_OCFAULT;

typedef enum : uint8_t

{

MAX31856_TCTYPE_B, // B type

MAX31856_TCTYPE_E, // E type

MAX31856_TCTYPE_J, // J type

MAX31856_TCTYPE_K, // K type (default)

MAX31856_TCTYPE_N, // N type

MAX31856_TCTYPE_R, // R type

MAX31856_TCTYPE_S, // S type

MAX31856_TCTYPE_T, // T type

MAX31856_TCTYPE_x8 = 0b1000, // voltage mode, amplifire x8, code = 8 x 1.6 x 2e17 x VIN

MAX31856_TCTYPE_x32 = 0b1100, // voltage mode, amplifire x32, code = 32 x 1.6 x 2e17 x VIN

} MAX31856_TCTYPE;

typedef enum : uint8_t

{

MAX31856_AVGSEL_1, // 1 sample (default)

MAX31856_AVGSEL_2, // 2 sample

MAX31856_AVGSEL_4, // 4 sample

MAX31856_AVGSEL_8, // 8 sample

MAX31856_AVGSEL_16, // 16 sample

} MAX31856_AVGSEL;

typedef union

{

struct

{

uint8_t TCTYPE:4;

uint8_t AVGSEL:3;

uint8_t RESERVED:1;

uint8_t FILTER:1;

uint8_t FAULTCLR:1;

uint8_t FAULT:1;

uint8_t CJ:1;

uint8_t OCFAULT:2;

uint8_t ONESHOT:1;

uint8_t CMODE:1;

} bit;

uint16_t reg;

} MAX31856_CR;

typedef union

{

struct

{

uint8_t OPEN:1;

uint8_t OVUV:1;

uint8_t TCLOW:1;

uint8_t TCHIGH:1;

uint8_t CJLOW:1;

uint8_t CJHIGH:1;

uint8_t RESERVED:2;

} bit;

uint8_t reg;

} MAX31856_MASK;

typedef union

{

struct

{

uint8_t OPEN:1;

uint8_t OVUV:1;

uint8_t TCLOW:1;

uint8_t TCHIGH:1;

uint8_t CJLOW:1;

uint8_t CJHIGH:1;

uint8_t TCRANGE:1;

uint8_t CJRANGE:1;

} bit;

uint8_t reg;

} MAX31856_SR;

typedef enum : uint8_t

{

MAX31856_STATUS_IDLE,

MAX31856_STATUS_BUSY,

MAX31856_STATUS_READY,

MAX31856_STATUS_FAULT,

} MAX31856_STATUS;

// conversion time

#define MAX31856_TCONV_SINGLE_50HZ 185000UL // TYP: 16900 MAX:185000

#define MAX31856_TCONV_SINGLE_60HZ 155000UL // TYP: 14300 MAX:155000

#define MAX31856_TCONV_CONTINUOUS_50HZ 110000UL // TYP: 98000 MAX:110000

#define MAX31856_TCONV_CONTINUOUS_60HZ 90000UL // TYP: 82000 MAX: 90000

#define MAX31856_TCONV_CJ(c) ((c) ? 25000UL : 0UL)

#define MAX31856_TCONV_SINGLE_AVGSEL(f, n) \

((f) == MAX31856_FILTER_60HZ ? (33333UL * ((1 << (n)) - 1)) : (40000UL * ((1 << (n)) - 1)))

#define MAX31856_TCONV_CONTINUOUS_AVGSEL(f, n) \

((f) == MAX31856_FILTER_60HZ ? (16666UL * ((1 << (n)) - 1)) : (20000UL * ((1 << (n)) - 1)))

#define MAX31856_TCONV_SINGLE(f, n, c) \

(((f) == MAX31856_FILTER_60HZ ? MAX31856_TCONV_SINGLE_60HZ : MAX31856_TCONV_SINGLE_50HZ) \

- MAX31856_TCONV_CJ(c) + MAX31856_TCONV_SINGLE_AVGSEL(f, n))

#define MAX31856_TCONV_CONTINUOUS(f, n, c) \

(((f) == MAX31856_FILTER_60HZ ? MAX31856_TCONV_CONTINUOUS_60HZ : MAX31856_TCONV_CONTINUOUS_50HZ) \

- MAX31856_TCONV_CJ(c) + MAX31856_TCONV_CONTINUOUS_AVGSEL(f, n))

// fault test time

#define MAX31856_TTEST_OCFAULT_CJ_ENABLE_1 15000UL // TYP: 13300 MAX: 15000

#define MAX31856_TTEST_OCFAULT_CJ_ENABLE_2 37000UL // TYP: 33400 MAX: 37000

#define MAX31856_TTEST_OCFAULT_CJ_ENABLE_3 125000UL // TYP:113400 MAX:125000

#define MAX31856_TTEST_OCFAULT_CJ_ENABLE(o) \

((o) == MAX31856_OCFAULT_LT_5K ? MAX31856_TTEST_OCFAULT_CJ_ENABLE_1 : \

((o) == MAX31856_OCFAULT_GT_5K_S ? MAX31856_TTEST_OCFAULT_CJ_ENABLE_2 : \

((o) == MAX31856_OCFAULT_GT_5K_L ? MAX31856_TTEST_OCFAULT_CJ_ENABLE_3 : \

0UL)))

#define MAX31856_TTEST_OCFAULT_CJ_DISABLE_1 44000UL // TYP: 40000 MAX: 44000

#define MAX31856_TTEST_OCFAULT_CJ_DISABLE_2 66000UL // TYP: 60000 MAX: 66000

#define MAX31856_TTEST_OCFAULT_CJ_DISABLE_3 154000UL // TYP:140000 MAX:154000

#define MAX31856_TTEST_OCFAULT_CJ_DISABLE(o) \

((o) == MAX31856_OCFAULT_LT_5K ? MAX31856_TTEST_OCFAULT_CJ_DISABLE_1 : \

((o) == MAX31856_OCFAULT_GT_5K_S ? MAX31856_TTEST_OCFAULT_CJ_DISABLE_2 : \

((o) == MAX31856_OCFAULT_GT_5K_L ? MAX31856_TTEST_OCFAULT_CJ_DISABLE_3 : \

0UL)))

#define MAX31856_TTEST_OCFAULT(c, o) \

((c) ? MAX31856_TTEST_OCFAULT_CJ_DISABLE(o) : MAX31856_TTEST_OCFAULT_CJ_ENABLE(o))

template

typename SPIBUS_T,

SPIBUS_T &SPIBUS,

int DRDY = -1,

MAX31856_TCTYPE TCTYPE = MAX31856_TCTYPE_K,

MAX31856_FILTER FILTER = MAX31856_FILTER_60HZ,

MAX31856_AVGSEL AVGSEL = MAX31856_AVGSEL_1,

MAX31856_OCFAULT OCFAULT = MAX31856_OCFAULT_LT_5K,

MAX31856_CJ CJ = MAX31856_CJ_ENABLE

class MAX31856

{

private:

MAX31856_CR _cr;

MAX31856_SR _sr;

MAX31856_MASK _mask;

int32_t _temp;

uint32_t _start;

uint32_t _tconv;

uint8_t _ready;

void write(MAX31856_REGISTER reg, uint8_t value)

{

uint8_t buf[] = {(uint8_t)(reg | MAX31856_REGISTER_W), value};

SPIBUS.write(buf, sizeof(buf));

}

void write16(MAX31856_REGISTER reg, uint16_t value)

{

uint8_t buf[] = {(uint8_t)(reg | MAX31856_REGISTER_W), (uint8_t)(value >> 8), (uint8_t)value};

SPIBUS.write(buf, sizeof(buf));

}

void write32(MAX31856_REGISTER reg, uint32_t value)

{

uint8_t buf[] = {(uint8_t)(reg | MAX31856_REGISTER_W), (uint8_t)(value >> 24), (uint8_t)(value >> 16), (uint8_t)(value >> 8), (uint8_t)value};

SPIBUS.write(buf, sizeof(buf));

}

uint8_t read(MAX31856_REGISTER reg)

{

uint8_t buf[] = {reg};

SPIBUS.writeAndRead(buf, 1, buf, sizeof(buf));

return buf[0];

}

uint16_t read16(MAX31856_REGISTER reg)

{

uint8_t buf[2] = {reg};

SPIBUS.writeAndRead(buf, 1, buf, sizeof(buf));

return ((uint16_t)buf[0] << 8) | buf[1];

}

uint32_t read32(MAX31856_REGISTER reg)

{

uint8_t buf[4] = {reg};

SPIBUS.writeAndRead(buf, 1, buf, sizeof(buf));

return ((uint32_t)buf[0] << 24) | ((uint32_t)buf[1] << 16) | ((uint16_t)buf[2] << 8) | buf[3];

}

void clear(void)

{

_cr.bit.FAULTCLR = 1;

write16(MAX31856_REGISTER_CR0, _cr.reg);

_cr.bit.FAULTCLR = 0;

}

bool readLT(void)

{

int32_t lt = (int32_t)read32(MAX31856_REGISTER_LTCBH);

_sr.reg = (uint8_t)lt;

if (TCTYPE & MAX31856_TCTYPE_x8)

_sr.bit.TCRANGE = 0;

if (_sr.reg)

{

clear();

return false;

}

if (TCTYPE & MAX31856_TCTYPE_x8)

_temp = ((int64_t)(lt >> 13) * 10000000) >> (4 + 17); // code = 1.6 x 2e17 x VIN

else

_temp = (lt >> 12) & ~1;

return true;

}

public:

MAX31856(void)

: _temp(0)

, _start(0)

, _tconv(0)

, _ready(0)

{

_sr.reg = 0;

_cr.reg = 0;

_cr.bit.FILTER = FILTER;

_cr.bit.FAULT = 1; // interrupt mode

_cr.bit.CJ = CJ;

_cr.bit.OCFAULT = OCFAULT;

_cr.bit.TCTYPE = TCTYPE;

_cr.bit.AVGSEL = AVGSEL;

_mask.reg = 0xFF;

}

virtual ~MAX31856(void)

{

}

void cj_offset(int8_t temp)

{

write(MAX31856_REGISTER_CJTO, (uint8_t)temp);

}

void cj_temperature(int16_t temp)

{

if (temp < (-64 << 8))

temp = (-64 << 8);

write16(MAX31856_REGISTER_CJTH, (uint16_t)temp);

}

int16_t cj_temperature(void)

{

return (int16_t)read16(MAX31856_REGISTER_CJTH);

}

void cj_threshold(int8_t low = -64, int8_t high = 127)

{

if (low < -64)

low = -64;

if (high < -64)

high = -64;

write16(MAX31856_REGISTER_CJHF, ((uint16_t)high << 8) | low);

}

void threshold(int16_t low = -32768, int16_t high = 32767)

{

write32(MAX31856_REGISTER_LTHFTH, ((uint32_t)high << 16) | low);

}

void fault_mask(MAX31856_MASK mask)

{

write(MAX31856_REGISTER_MASK, _mask = mask);

}

MAX31856_MASK fault_mask(void)

{

return _mask;

}

bool oneshot(void)

{

// start one short

_tconv = 0;

_cr.bit.CMODE = 0;

_cr.bit.ONESHOT = 1;

write16(MAX31856_REGISTER_CR0, _cr.reg);

_cr.bit.ONESHOT = 0;

if (DRDY >= 0)

{

uint32_t t = micros();

uint8_t d = digitalRead(DRDY);

{

// detect falling edge

if (d != digitalRead(DRDY))

{

d = !d;

if (!d)

break;

}

yield();

}

while (micros() - t < MAX31856_TCONV_SINGLE(FILTER, AVGSEL, CJ) + MAX31856_TTEST_OCFAULT(CJ, OCFAULT));

}

else

{

#if defined(__GNUC__)

#pragma GCC diagnostic push

#pragma GCC diagnostic ignored "-Woverflow"

#endif

delayMicroseconds(MAX31856_TCONV_SINGLE(FILTER, AVGSEL, CJ) + MAX31856_TTEST_OCFAULT(CJ, OCFAULT));

#if defined(__GNUC__)

#pragma GCC diagnostic pop

#endif

}

return readLT();

}

void start(void)

{

// start continuous mode

_ready = 0;

_tconv = MAX31856_TCONV_SINGLE(FILTER, AVGSEL, CJ) + MAX31856_TTEST_OCFAULT(CJ, OCFAULT);

_cr.bit.CMODE = 1;

write16(MAX31856_REGISTER_CR0, _cr.reg);

_start = micros();

if (DRDY >= 0)

_ready = digitalRead(DRDY);

}

void stop(void)

{

_tconv = 0;

_cr.bit.CMODE = 0;

write16(MAX31856_REGISTER_CR0, _cr.reg);

}

int32_t temperature(void)

{

return _temp;

}

MAX31856_SR status(void)

{

return _sr;

}

MAX31856_STATUS handle(void)

{

if (_tconv == 0)

return MAX31856_STATUS_IDLE;

if (micros() - _start >= _tconv)

_start += _tconv;

else

{

if (DRDY < 0)

return MAX31856_STATUS_BUSY;

// detect falling edge

if (_ready == digitalRead(DRDY))

return MAX31856_STATUS_BUSY;

_ready = !_ready;

if (_ready)

return MAX31856_STATUS_BUSY;

_start = micros();

}

_tconv = MAX31856_TCONV_CONTINUOUS(FILTER, AVGSEL, CJ) + MAX31856_TTEST_OCFAULT(CJ, OCFAULT);

return readLT() ? MAX31856_STATUS_READY : MAX31856_STATUS_FAULT;

}

};

#endif

【参照ライブラリ】
Arduino用のSPI/TWI共通インターフェース・クラスを作ってみた。

月: 2020年11月

MAX31856(熱電対)ライブラリを作ってみた。