2020年10月 – ページ 2

MAX31865と言えば互換(パクリ？)モジュールも沢山でているAdafruitが有名だ。

Adafruit PT100 RTD Temperature Sensor Amplifier – MAX31865

有名すぎてほぼ一択みたいな感じになってる感もあるが、肝心のソフトウェアがイマイチである。他にも公開されてる物がそれなりにあるが、どれもこれもなんとなくスッキリしない。

個人の感想でしかないので全否定するつもりもないし設計通りには動作するのだろうが．．．何がイマイチなのかは次の通り。

・無駄な処理が多すぎる。⇒恐らく実行時間の半分は無駄な時間。
・デバイスの機能をそのままライブラリ化してるだけ。⇒使いやすいとは言えない。
・浮動小数点演算を多用している。⇒非力なMPUに適さない。
・温度を取得する度に合計75msものdelay()を実行している。⇒他の処理と並行できない。
・連続変換モードに対応できていない。⇒なぜ？

Adafruitのライブラリはとりあえず動作検証はできまっせ的なレベルのものが多いように感じる。恐らく組み込み系の経験があまりないＰＣ系メインの外注さんに作らせているのかな。組み込み系のエンジニアならああいう感じのコードは書かないと思う。という私もＰＣ系のほうが長くて組み込み系なんて数年？程度の経験しかないのであまり人のことは言えませんが．．．(-_-;)

とはいえ、何もないよりはましなので感謝は忘れずに。ですね。

【仕様】
・温度センサー … PT100専用
・温度計測範囲 … 約-30～300℃

※温度計測時にフォールト検出も行う。フォールト中は温度計測は行われず、温度計測中にフォールトになった場合はフォールト解除後に温度計測が再開される。

※本ライブラリはSPIBUSライブラリ経由で動作する。Arduino標準のSPIライブラリ用に実装してある。仕様の異なる他のSPIライブラリを使いたい場合は、SPIBUSライブラリを書き換えれば良い。

購入したのはこれ⇒PT100〜PT1000 MAX31865 RTD プラチナ抵抗温度検出器熱電対センサーアンプモジュール

【概要】

void threshold(int16_t low, int16_t high)

1	void threshold(int16_t low, int16_t high)

最低温度と最大温度を16倍された温度(小数部含む)で設定する。範囲外になるとフォールトが発生する。

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(bool vbias = false)

1	void stop(bool vbias = false)

連続変換モードを停止する。vbiasにfalseを指定するとほんの気持ちだけ省電力化(約0.5mA程度)できる。

int16_t temperature(void)

1	int16_t temperature(void)

計測した温度を取得する。温度は16倍されていることに注意すべし。

MAX31865_FAULT_STATUS status(void)

1	MAX31865_FAULT_STATUS status(void)

検出したフォールト・ステータスを取得する。

MAX31865_STATUS handle(void)

1	MAX31865_STATUS handle(void)

連続変換モードを処理する。戻り値は次の通り。
MAX31865_STATUS_IDLE … 停止中。
MAX31865_STATUS_BUSY … 計測中
MAX31865_STATUS_READY … 計測完了。temperature()で温度を取得できる。
MAX31865_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 "max31865.h"
#include "spibus.h"

#define CS_PIN 10  // A10

#define SPIBUS SPIBUS<CS_PIN, MAX31865_SPI_CLOCK>

SPIBUS spi;
MAX31865<SPIBUS, spi, -1, MAX31865_RTD_3WIRE, MAX31865_FILTER_60HZ> rtd;

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

void loop()
{
  MAX31865_FAULT_STATUS fault;
  switch (rtd.handle())
  {
    case MAX31865_STATUS_READY:
      Serial.print("temp = ");
      Serial.println(rtd.temperature() / 16.0);
      delay(500);
      break;
    case MAX31865_STATUS_FAULT:
      fault = rtd.status();
      Serial.print("fault = 0x");
      if (fault.reg < 10)
        Serial.print("0");
      Serial.println(fault.reg, HEX);
      delay(500);
      break;
    default:
      break;
  }
}

#include "max31865.h"

#include "spibus.h"

#define CS_PIN 10 // A10

#define SPIBUS SPIBUS<CS_PIN, MAX31865_SPI_CLOCK>

SPIBUS spi;

MAX31865<SPIBUS, spi, -1, MAX31865_RTD_3WIRE, MAX31865_FILTER_60HZ> rtd;

void setup()

{

uint32_t t = millis();

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

continue;

spi.begin();

rtd.start();

}

void loop()

{

MAX31865_FAULT_STATUS fault;

switch (rtd.handle())

{

case MAX31865_STATUS_READY:

Serial.print("temp = ");

Serial.println(rtd.temperature() / 16.0);

delay(500);

break;

case MAX31865_STATUS_FAULT:

fault = rtd.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】
2020-11-15
記述ミスによりがコンパイルできなくなっていたため修正。

2020-11-12
DRDYピンを利用できるよう改良してみた。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．．．

【ライブラリ】

/*
  max31865.h - RTD Sensor Library for MAX31865

  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 __MAX31865_H
#define __MAX31865_H

#include <stdint.h>
#include <stdbool.h>
#include "pt100.h"

#define MAX31865_SPI_CLOCK 5000000

typedef enum : uint8_t
{
  MAX31865_REGISTER_CONFIGURATION,
  MAX31865_REGISTER_RTD_MSB,
  MAX31865_REGISTER_RTD_LSB,
  MAX31865_REGISTER_HIGH_FAULT_THERESHOLD_MSB,
  MAX31865_REGISTER_HIGH_FAULT_THERESHOLD_LSB,
  MAX31865_REGISTER_LOW_FAULT_THERESHOLD_MSB,
  MAX31865_REGISTER_LOW_FAULT_THERESHOLD_LSB,
  MAX31865_REGISTER_FAULT_STATUS,
} MAX31865_REGISTER;

#define MAX31865_REGISTER_W 0x80

typedef enum : uint8_t
{
  MAX31865_FILTER_60HZ,
  MAX31865_FILTER_50HZ,
} MAX31865_FILTER;

typedef enum : uint8_t
{
  MAX31865_RTD_2WIRE,
  MAX31865_RTD_3WIRE,
  MAX31865_RTD_4WIRE = MAX31865_RTD_2WIRE,
} MAX31865_RTD;

typedef enum : uint8_t
{
  MAX31865_FAULT_DETECT_NO_ACTION,
  MAX31865_FAULT_DETECT_AUTOMATIC,
  MAX31865_FAULT_DETECT_MANUAL,
  MAX31865_FAULT_DETECT_FINISH,
} MAX31865_FAULT_DETECT;

typedef union
{
  struct
  {
    uint8_t reserved:2;
    uint8_t over_under_voltage:1;
    uint8_t rtdin_lt_vbias:1; // FORCE open
    uint8_t refin_lt_vbias:1; // FORCE open
    uint8_t refin_gt_vbias:1;
    uint8_t rtd_low_threshold:1;
    uint8_t rtd_high_threshold:1;
  } bit;
  uint8_t reg;
} MAX31865_FAULT_STATUS;

typedef enum : uint8_t
{
  MAX31865_STATUS_IDLE,
  MAX31865_STATUS_BUSY,
  MAX31865_STATUS_READY,
  MAX31865_STATUS_FAULT,
} MAX31865_STATUS;

#define MAX31865_TCONV_SINGLE_50HZ     66000 // TYPE:62500 MAX:66000
#define MAX31865_TCONV_SINGLE_60HZ     55000 // TYPE:52000 MAX:55000
#define MAX31865_TCONV_CONTINUOUS_50HZ 21000 // TYPE:20000 MAX:21000
#define MAX31865_TCONV_CONTINUOUS_60HZ 17600 // TYPE:16700 MAX:17600
#define MAX31865_TCONV_SINGLE(f)       ((f) == MAX31865_FILTER_60HZ ? MAX31865_TCONV_SINGLE_60HZ : MAX31865_TCONV_SINGLE_50HZ)
#define MAX31865_TCONV_CONTINUOUS(f)   ((f) == MAX31865_FILTER_60HZ ? MAX31865_TCONV_CONTINUOUS_60HZ : MAX31865_TCONV_CONTINUOUS_50HZ)

typedef union
{
  struct
  {
    uint8_t filter:1;          // 1 = 50Hz, 0 = 60Hz
    uint8_t status_clear:1;    // 1 = Clear(auto-clear)
    uint8_t fault_detection:2; // 3 = Finish, 2 = Auto, 1= Manual, 0 = No Action
    uint8_t rtd:1;             // 1 = 3-wire RTD, 0 = 2-wire or 4-wire
    uint8_t one_shot:1;        // 1 = 1-shot(auto-clear)
    uint8_t conversion_mode:1; // 1 = Auto, 0 = Normally off
    uint8_t vbias:1;           // 1 = ON, 0 = OFF
  } bit;
  uint8_t reg;
} MAX31865_CONFIG;

/*
  RCTIME ... time constant (us) of RC filter (R ohm x C uF)

    exsample: 1000ohm x 0.01uF = 1000 x 0.01 = 10 us
*/
template
<
  typename SPIBUS_T,
  SPIBUS_T &SPIBUS,
  int DRDY = -1,
  MAX31865_RTD RTD = MAX31865_RTD_3WIRE,
  MAX31865_FILTER FILTER = MAX31865_FILTER_60HZ,
  uint16_t RCTIME = 0,
  uint16_t RREF = 430
>
class MAX31865
{
  private:

    MAX31865_CONFIG       _config;
    uint32_t              _start;
    uint32_t              _tconv;
    uint16_t              _temp;
    MAX31865_FAULT_STATUS _status;
    uint8_t               _ready;

    void write(MAX31865_REGISTER reg, uint8_t value)
    {
      uint8_t buf[] = {(uint8_t)(reg | MAX31865_REGISTER_W), value};
      SPIBUS.write(buf, sizeof(buf));
    }

    void write16(MAX31865_REGISTER reg, uint16_t value)
    {
      uint8_t buf[] = {(uint8_t)(reg | MAX31865_REGISTER_W), value >> 8, value & 0xFF};
      SPIBUS.write(buf, sizeof(buf));
    }

    uint8_t read(MAX31865_REGISTER reg)
    {
      uint8_t buf[] = {reg};
      SPIBUS.writeAndRead(buf, 1, buf, sizeof(buf));
      return buf[0];
    }

    uint16_t read16(MAX31865_REGISTER reg)
    {
      uint8_t buf[2] = {reg};
      SPIBUS.writeAndRead(buf, 1, buf, sizeof(buf));
      return ((uint16_t)buf[0] << 8) | buf[1];
    }

    void vbias(void)
    {
      if (_config.bit.vbias == 0)
      {
        _config.bit.vbias = 1;
        write(MAX31865_REGISTER_CONFIGURATION, _config.reg);
        delayMicroseconds(RCTIME * 10 + (RCTIME >> 1) + 1000);
      }
    }

    bool readRTD(void)
    {
      uint16_t rtd = read16(MAX31865_REGISTER_RTD_MSB);
      if (rtd & 1)
      {
        fault();
        _status.bit.reserved = 1; // fault dummy flag
        return false;
      }
      _temp = PT100::temperature(((uint32_t)(rtd >> 1) * RREF) >> (15 - PT100_DATA_SHIFT));
      return true;
    }

    bool fault(void)
    {
      // save conversion mode
      uint8_t mode = _config.bit.conversion_mode;
      // clear fault status
      stop(false);
      // vbias on
      vbias();
      // fault detection
      if (RCTIME * 5 <= 100)
      {
        // auto detect
        _config.bit.fault_detection = MAX31865_FAULT_DETECT_AUTOMATIC;
        write(MAX31865_REGISTER_CONFIGURATION, _config.reg);
        delayMicroseconds(600);
      }
      else
      {
        // manual detect
        delayMicroseconds(RCTIME * 5 - 100);
        _config.bit.fault_detection = MAX31865_FAULT_DETECT_MANUAL;
        write(MAX31865_REGISTER_CONFIGURATION, _config.reg);
        delayMicroseconds(RCTIME * 5 - 100);
        _config.bit.fault_detection = MAX31865_FAULT_DETECT_FINISH;
        write(MAX31865_REGISTER_CONFIGURATION, _config.reg);
        delayMicroseconds(100);
      }
      _config.bit.fault_detection = MAX31865_FAULT_DETECT_NO_ACTION;
      // read fault status
      _status.reg = read(MAX31865_REGISTER_FAULT_STATUS);
      _status.bit.reserved = 0;
      // restore conversion mode
      _config.bit.conversion_mode = mode;
      return _status.reg != 0;
    }

    bool hasFault(bool restart)
    {
      if (status().reg != 0)
      {
        if (fault())
          return true;
        // restart continuous conversion
        if (restart)
          start();
      }
      return false;
    }

  public:

    MAX31865(void)
    : _start(0)
    , _tconv(0)
    , _temp(0)
    , _ready(0)
    {
      _status.reg = 0;
      _config.reg = 0;
      _config.bit.filter          = FILTER;
      _config.bit.fault_detection = MAX31865_FAULT_DETECT_NO_ACTION;
      _config.bit.rtd             = RTD;
    }

    virtual ~MAX31865(void)
    {
    }

    void threshold(int16_t low = PT100_TEMP_LOW - 1, int16_t high = PT100_TEMP_HIGH + 1)
    {
      if (low < PT100_TEMP_LOW)
        low = 0x0000;
      else if (low > PT100_TEMP_HIGH)
        low = 0xFFFF;
      else
        low = ((uint32_t)PT100::resistor(low) << (15 - PT100_DATA_SHIFT)) / RREF;
      if (high < PT100_TEMP_LOW)
        high = 0x0000;
      else if (high > PT100_TEMP_HIGH)
        high = 0xFFFF;
      else
        high = ((uint32_t)PT100::resistor(high) << (15 - PT100_DATA_SHIFT)) / RREF;
      write16(MAX31865_REGISTER_HIGH_FAULT_THERESHOLD_MSB, (uint16_t)high);
      write16(MAX31865_REGISTER_LOW_FAULT_THERESHOLD_MSB , (uint16_t)low );
    }

    bool oneshot(void)
    {
      if (hasFault(false))
        return false;
      // vbias on
      vbias();
      // start one short
      _config.bit.conversion_mode = 0;
      _config.bit.one_shot = 1;
      write(MAX31865_REGISTER_CONFIGURATION, _config.reg);
      _config.bit.one_shot = 0;
      _tconv = 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 < MAX31865_TCONV_SINGLE(FILTER));
      }
      else
      {
        delayMicroseconds(MAX31865_TCONV_SINGLE(FILTER));
      }
      return readRTD();
    }

    void start(void)
    {
      // vbias on
      vbias();
      // start auto mode
      _config.bit.conversion_mode = 1;
      write(MAX31865_REGISTER_CONFIGURATION, _config.reg);
      _start = micros();
      _tconv = MAX31865_TCONV_SINGLE(FILTER);
      if (DRDY >= 0)
        _ready  = digitalRead(DRDY);
    }

    void stop(bool vbias = false)
    {
      if (!vbias)
        _config.bit.vbias = 0;
      _config.bit.conversion_mode = 0;
      _config.bit.status_clear = 1;
      write(MAX31865_REGISTER_CONFIGURATION, _config.reg);
      _config.bit.status_clear = 0;
      _tconv = 0;
    }

    int16_t temperature(void)
    {
      return _temp;
    }

    MAX31865_FAULT_STATUS status(void)
    {
      return _status;
    }

    MAX31865_STATUS handle(void)
    {
      if (hasFault(_config.bit.conversion_mode))
        return MAX31865_STATUS_FAULT;
      if (_tconv == 0)
        return MAX31865_STATUS_IDLE;
      if (micros() - _start >= _tconv)
        _start += _tconv;
      else
      {
        if (DRDY < 0)
          return MAX31865_STATUS_BUSY;
        // detect falling edge
        if (_ready == digitalRead(DRDY))
          return MAX31865_STATUS_BUSY;
        _ready = !_ready;
        if (_ready)
          return MAX31865_STATUS_BUSY;
        _start = micros();
      }
      _tconv = MAX31865_TCONV_CONTINUOUS(FILTER);
      return readRTD() ? MAX31865_STATUS_READY : MAX31865_STATUS_FAULT;
    }
};

#endif

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max31865.h - RTD Sensor Library for MAX31865

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 __MAX31865_H

#define __MAX31865_H

#include <stdint.h>

#include <stdbool.h>

#include "pt100.h"

#define MAX31865_SPI_CLOCK 5000000

typedef enum : uint8_t

{

MAX31865_REGISTER_CONFIGURATION,

MAX31865_REGISTER_RTD_MSB,

MAX31865_REGISTER_RTD_LSB,

MAX31865_REGISTER_HIGH_FAULT_THERESHOLD_MSB,

MAX31865_REGISTER_HIGH_FAULT_THERESHOLD_LSB,

MAX31865_REGISTER_LOW_FAULT_THERESHOLD_MSB,

MAX31865_REGISTER_LOW_FAULT_THERESHOLD_LSB,

MAX31865_REGISTER_FAULT_STATUS,

} MAX31865_REGISTER;

#define MAX31865_REGISTER_W 0x80

typedef enum : uint8_t

{

MAX31865_FILTER_60HZ,

MAX31865_FILTER_50HZ,

} MAX31865_FILTER;

typedef enum : uint8_t

{

MAX31865_RTD_2WIRE,

MAX31865_RTD_3WIRE,

MAX31865_RTD_4WIRE = MAX31865_RTD_2WIRE,

} MAX31865_RTD;

typedef enum : uint8_t

{

MAX31865_FAULT_DETECT_NO_ACTION,

MAX31865_FAULT_DETECT_AUTOMATIC,

MAX31865_FAULT_DETECT_MANUAL,

MAX31865_FAULT_DETECT_FINISH,

} MAX31865_FAULT_DETECT;

typedef union

{

struct

{

uint8_t reserved:2;

uint8_t over_under_voltage:1;

uint8_t rtdin_lt_vbias:1; // FORCE open

uint8_t refin_lt_vbias:1; // FORCE open

uint8_t refin_gt_vbias:1;

uint8_t rtd_low_threshold:1;

uint8_t rtd_high_threshold:1;

} bit;

uint8_t reg;

} MAX31865_FAULT_STATUS;

typedef enum : uint8_t

{

MAX31865_STATUS_IDLE,

MAX31865_STATUS_BUSY,

MAX31865_STATUS_READY,

MAX31865_STATUS_FAULT,

} MAX31865_STATUS;

#define MAX31865_TCONV_SINGLE_50HZ 66000 // TYPE:62500 MAX:66000

#define MAX31865_TCONV_SINGLE_60HZ 55000 // TYPE:52000 MAX:55000

#define MAX31865_TCONV_CONTINUOUS_50HZ 21000 // TYPE:20000 MAX:21000

#define MAX31865_TCONV_CONTINUOUS_60HZ 17600 // TYPE:16700 MAX:17600

#define MAX31865_TCONV_SINGLE(f) ((f) == MAX31865_FILTER_60HZ ? MAX31865_TCONV_SINGLE_60HZ : MAX31865_TCONV_SINGLE_50HZ)

#define MAX31865_TCONV_CONTINUOUS(f) ((f) == MAX31865_FILTER_60HZ ? MAX31865_TCONV_CONTINUOUS_60HZ : MAX31865_TCONV_CONTINUOUS_50HZ)

typedef union

{

struct

{

uint8_t filter:1; // 1 = 50Hz, 0 = 60Hz

uint8_t status_clear:1; // 1 = Clear(auto-clear)

uint8_t fault_detection:2; // 3 = Finish, 2 = Auto, 1= Manual, 0 = No Action

uint8_t rtd:1; // 1 = 3-wire RTD, 0 = 2-wire or 4-wire

uint8_t one_shot:1; // 1 = 1-shot(auto-clear)

uint8_t conversion_mode:1; // 1 = Auto, 0 = Normally off

uint8_t vbias:1; // 1 = ON, 0 = OFF

} bit;

uint8_t reg;

} MAX31865_CONFIG;

RCTIME ... time constant (us) of RC filter (R ohm x C uF)

exsample: 1000ohm x 0.01uF = 1000 x 0.01 = 10 us

template

typename SPIBUS_T,

SPIBUS_T &SPIBUS,

int DRDY = -1,

MAX31865_RTD RTD = MAX31865_RTD_3WIRE,

MAX31865_FILTER FILTER = MAX31865_FILTER_60HZ,

uint16_t RCTIME = 0,

uint16_t RREF = 430

class MAX31865

{

private:

MAX31865_CONFIG _config;

uint32_t _start;

uint32_t _tconv;

uint16_t _temp;

MAX31865_FAULT_STATUS _status;

uint8_t _ready;

void write(MAX31865_REGISTER reg, uint8_t value)

{

uint8_t buf[] = {(uint8_t)(reg | MAX31865_REGISTER_W), value};

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

}

void write16(MAX31865_REGISTER reg, uint16_t value)

{

uint8_t buf[] = {(uint8_t)(reg | MAX31865_REGISTER_W), value >> 8, value & 0xFF};

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

}

uint8_t read(MAX31865_REGISTER reg)

{

uint8_t buf[] = {reg};

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

return buf[0];

}

uint16_t read16(MAX31865_REGISTER reg)

{

uint8_t buf[2] = {reg};

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

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

}

void vbias(void)

{

if (_config.bit.vbias == 0)

{

_config.bit.vbias = 1;

write(MAX31865_REGISTER_CONFIGURATION, _config.reg);

delayMicroseconds(RCTIME * 10 + (RCTIME >> 1) + 1000);

}

bool readRTD(void)

{

uint16_t rtd = read16(MAX31865_REGISTER_RTD_MSB);

if (rtd & 1)

{

fault();

_status.bit.reserved = 1; // fault dummy flag

return false;

}

_temp = PT100::temperature(((uint32_t)(rtd >> 1) * RREF) >> (15 - PT100_DATA_SHIFT));

return true;

}

bool fault(void)

{

// save conversion mode

uint8_t mode = _config.bit.conversion_mode;

// clear fault status

stop(false);

// vbias on

vbias();

// fault detection

if (RCTIME * 5 <= 100)

{

// auto detect

_config.bit.fault_detection = MAX31865_FAULT_DETECT_AUTOMATIC;

write(MAX31865_REGISTER_CONFIGURATION, _config.reg);

delayMicroseconds(600);

}

else

{

// manual detect

delayMicroseconds(RCTIME * 5 - 100);

_config.bit.fault_detection = MAX31865_FAULT_DETECT_MANUAL;

write(MAX31865_REGISTER_CONFIGURATION, _config.reg);

delayMicroseconds(RCTIME * 5 - 100);

_config.bit.fault_detection = MAX31865_FAULT_DETECT_FINISH;

write(MAX31865_REGISTER_CONFIGURATION, _config.reg);

delayMicroseconds(100);

}

_config.bit.fault_detection = MAX31865_FAULT_DETECT_NO_ACTION;

// read fault status

_status.reg = read(MAX31865_REGISTER_FAULT_STATUS);

_status.bit.reserved = 0;

// restore conversion mode

_config.bit.conversion_mode = mode;

return _status.reg != 0;

}

bool hasFault(bool restart)

{

if (status().reg != 0)

{

if (fault())

return true;

// restart continuous conversion

if (restart)

start();

}

return false;

}

public:

MAX31865(void)

: _start(0)

, _tconv(0)

, _temp(0)

, _ready(0)

{

_status.reg = 0;

_config.reg = 0;

_config.bit.filter = FILTER;

_config.bit.fault_detection = MAX31865_FAULT_DETECT_NO_ACTION;

_config.bit.rtd = RTD;

}

virtual ~MAX31865(void)

{

}

void threshold(int16_t low = PT100_TEMP_LOW - 1, int16_t high = PT100_TEMP_HIGH + 1)

{

if (low < PT100_TEMP_LOW)

low = 0x0000;

else if (low > PT100_TEMP_HIGH)

low = 0xFFFF;

else

low = ((uint32_t)PT100::resistor(low) << (15 - PT100_DATA_SHIFT)) / RREF;

if (high < PT100_TEMP_LOW)

high = 0x0000;

else if (high > PT100_TEMP_HIGH)

high = 0xFFFF;

else

high = ((uint32_t)PT100::resistor(high) << (15 - PT100_DATA_SHIFT)) / RREF;

write16(MAX31865_REGISTER_HIGH_FAULT_THERESHOLD_MSB, (uint16_t)high);

write16(MAX31865_REGISTER_LOW_FAULT_THERESHOLD_MSB , (uint16_t)low );

}

bool oneshot(void)

{

if (hasFault(false))

return false;

// vbias on

vbias();

// start one short

_config.bit.conversion_mode = 0;

_config.bit.one_shot = 1;

write(MAX31865_REGISTER_CONFIGURATION, _config.reg);

_config.bit.one_shot = 0;

_tconv = 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 < MAX31865_TCONV_SINGLE(FILTER));

}

else

{

delayMicroseconds(MAX31865_TCONV_SINGLE(FILTER));

}

return readRTD();

}

void start(void)

{

// vbias on

vbias();

// start auto mode

_config.bit.conversion_mode = 1;

write(MAX31865_REGISTER_CONFIGURATION, _config.reg);

_start = micros();

_tconv = MAX31865_TCONV_SINGLE(FILTER);

if (DRDY >= 0)

_ready = digitalRead(DRDY);

}

void stop(bool vbias = false)

{

if (!vbias)

_config.bit.vbias = 0;

_config.bit.conversion_mode = 0;

_config.bit.status_clear = 1;

write(MAX31865_REGISTER_CONFIGURATION, _config.reg);

_config.bit.status_clear = 0;

_tconv = 0;

}

int16_t temperature(void)

{

return _temp;

}

MAX31865_FAULT_STATUS status(void)

{

return _status;

}

MAX31865_STATUS handle(void)

{

if (hasFault(_config.bit.conversion_mode))

return MAX31865_STATUS_FAULT;

if (_tconv == 0)

return MAX31865_STATUS_IDLE;

if (micros() - _start >= _tconv)

_start += _tconv;

else

{

if (DRDY < 0)

return MAX31865_STATUS_BUSY;

// detect falling edge

if (_ready == digitalRead(DRDY))

return MAX31865_STATUS_BUSY;

_ready = !_ready;

if (_ready)

return MAX31865_STATUS_BUSY;

_start = micros();

}

_tconv = MAX31865_TCONV_CONTINUOUS(FILTER);

return readRTD() ? MAX31865_STATUS_READY : MAX31865_STATUS_FAULT;

}

};

#endif

【参照ライブラリ】
PT100(白金ＲＴＤ)の抵抗値から温度へ変換するライブラリ
 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10月

MAX31865(PT100)ライブラリを作ってみた。