Class: MAX31856

Inherits:
Object
  • Object
show all
Defined in:
lib/max31856.rb,
lib/max31856/version.rb

Overview

MAX31856

Constant Summary collapse

TC_RES =

Thermocouple Temperature Data Resolution

0.0078125
CJ_RES =

Cold-Junction Temperature Data Resolution

0.015625
REG_CJ =

Fault status register

0x08
REG_TC =

Fault status register

0x0c
REG_FAULT =

Fault status register

0x0F
REG_1 =

Config Register 1

bit 7: Conversion Mode -> 0 (Normally Off Mode) bit 6: 1-shot -> 1 (ON) bit 5: open-circuit fault detection -> 0 (off) bit 4: open-circuit fault detection -> 0 (off) bit 3: Cold-junction temerature sensor enabled -> 0 (default) bit 2: Fault Mode -> 0 (default) bit 1: fault status clear -> 1 (clear any fault) bit 0: 50/60 Hz filter select -> 0 (60Hz)

[0x00, 0b01000010].freeze
REG_2 =

Config Register 2

bit 7: Reserved -> 0 bit 6: Averaging Mode 1 Sample -> 0 (default) bit 5: Averaging Mode 1 Sample -> 0 (default) bit 4: Averaging Mode 1 Sample -> 0 (default) bit 3: Thermocouple Type -> K Type (default) -> 0 (default) bit 2: Thermocouple Type -> K Type (default) -> 0 (default) bit 1: Thermocouple Type -> K Type (default) -> 1 (default) bit 0: Thermocouple Type -> K Type (default) -> 1 (default)

0x01
TYPES = 
{
  b: 0x00,
  e: 0x01,
  j: 0x02,
  k: 0x03,
  n: 0x04,
  r: 0x05,
  s: 0x06,
  t: 0x07
}.freeze
CHIPS = 
{
  0 => PiPiper::Spi::CHIP_SELECT_0,
  1 => PiPiper::Spi::CHIP_SELECT_1,
  2 => PiPiper::Spi::CHIP_SELECT_BOTH,
  3 => PiPiper::Spi::CHIP_SELECT_NONE
}.freeze
FAULTS = 
{
  0x80 => 'Cold Junction Out-of-Range',
  0x40 => 'Thermocouple Out-of-Range',
  0x20 => 'Cold-Junction High Fault',
  0x10 => 'Cold-Junction Low Fault',
  0x08 => 'Thermocouple Temperature High Fault',
  0x04 => 'Thermocouple Temperature Low Fault',
  0x02 => 'Overvoltage or Undervoltage Input Fault',
  0x01 => 'Thermocouple Open-Circuit Fault'
}.freeze
VERSION = 
'0.1.0'.freeze

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(type = :k, chip = 0, clock = 2_000_000) ⇒ MAX31856

Returns a new instance of MAX31856.



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# File 'lib/max31856.rb', line 76

def initialize(type = :k, chip = 0, clock = 2_000_000)
  @type = TYPES[type]
  @chip = CHIPS[chip]
  @clock = clock
end

Instance Attribute Details

#chip ⇒ Object

Returns the value of attribute chip.



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# File 'lib/max31856.rb', line 8

def chip
  @chip
end

#clock ⇒ Object

Returns the value of attribute clock.



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# File 'lib/max31856.rb', line 8

def clock
  @clock
end

#type ⇒ Object

Returns the value of attribute type.



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# File 'lib/max31856.rb', line 8

def type
  @type
end

Instance Method Details

#config ⇒ Object 



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# File 'lib/max31856.rb', line 102

def config
  spi_work do |spi|
    spi.write(REG_2, type)
    spi.write(REG_1)
  end
  sleep(0.2) # give it 200ms for conversion
end

#read ⇒ Object 



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# File 'lib/max31856.rb', line 110

def read
  tc = cj = 0
  spi_work do |spi|
    cj = read_cj(spi.write(Array.new(4, 0xff).unshift(REG_CJ)))
    sleep 0.2
    tc = read_tc(spi.write(Array.new(4, 0xff).unshift(REG_TC)))
  end
  [tc, cj]
end

#read_cj(raw) ⇒ Object 



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# File 'lib/max31856.rb', line 120

def read_cj(raw)
  lb, mb, _offset = raw.reverse # Offset already on sum
  # MSB << 8 | LSB and remove last 2
  temp = ((mb << 8) | lb) >> 2

  # Handle negative
  temp -= 0x4000 unless (mb & 0x80).zero?

  # Convert to Celsius
  temp * CJ_RES
end

#read_fault ⇒ Object

Read register faults



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# File 'lib/max31856.rb', line 148

def read_fault
  spi_work do |spi|
    fault = spi.write(REG_FAULT, 0xff)
    p [fault, fault.last.to_s(2).rjust(8, '0')]
  end
end

#read_tc(raw) ⇒ Object 



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# File 'lib/max31856.rb', line 132

def read_tc(raw)
  fault, lb, mb, hb = raw.reverse
  FAULTS.each do |f, txt|
    raise txt if fault & f == 1
  end
  # MSB << 8 | LSB and remove last 5
  temp = ((hb << 16) | (mb << 8) | lb) >> 5

  # Handle negative
  temp -= 0x80000 unless (hb & 0x80).zero?

  # Convert to Celsius
  temp * TC_RES
end

#spi_work ⇒ Object 



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# File 'lib/max31856.rb', line 82

def spi_work
  PiPiper::Spi.begin do |spi|
    # Set cpol, cpha
    PiPiper::Spi.set_mode(0, 1)

    # Setup the chip select behavior
    spi.chip_select_active_low(true)

    # Set the bit order to MSB
    spi.bit_order PiPiper::Spi::MSBFIRST

    # Set the clock divider to get a clock speed of 2MHz
    spi.clock clock

    spi.chip_select(chip) do
      yield spi
    end
  end
end