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//! # max31855 //! //! Driver for [MAX31855 thermocouple converter](https://www.maximintegrated.com/en/products/sensors/MAX31855.html) using traits from `embedded-hal`. //! //! ## Features //! * Read thermocouple temperature //! * Read internal reference junction temperature //! * Read fault data (missing thermocouple, short to ground or short to vcc) //! * Supports 16-bit (thermocouple + fault only) or 32-bit (thermocouple, internal and full fault details) //! * Supports Celsius, Fahrenheit or Kelvin units //! * Supports returning raw (ADC count) readings //! //! ## Example: //! ``` //! let freq: Hertz = 4.mhz().into(); //! let mode = Mode { //! polarity: Polarity::IdleLow, //! phase: Phase::CaptureOnFirstTransition //! }; //! //! let mut spi = Spi::spi2( //! device.SPI2, //! (sck_pin, miso_pin, mosi_pin) //! mode, //! freq, //! clocks, //! &mut rcc.apb1 //! ); //! //! // Full 32-bit read, result contains both thermocouple and internal temperatures //! match spi.read_all(&mut cs_pin, Unit::Celsius) { //! Ok(v) => info!("Ok: {:?}", v), //! Err(e) => info!("Err: {:?}", e), //! } //! //! // Just thermocouple 16-bit read //! match spi.read_thermocouple(&mut cs_pin, Unit::Celsius) { //! Ok(v) => info!("Ok: {:?}", v), //! Err(e) => info!("Err: {:?}", e), //! } //! ``` #![no_std] #![deny(warnings, missing_docs)] use embedded_hal::{ blocking::spi::Transfer, digital::v2::OutputPin, }; use bit_field::BitField; use core::ops::RangeInclusive; /// The bits that represent the thermocouple value when reading the first u16 from the sensor const THERMOCOUPLE_BITS: RangeInclusive<usize> = 2..=15; /// The bit that indicates some kind of fault when reading the first u16 from the sensor const FAULT_BIT: usize = 0; /// The bits that represent the internal value when reading the second u16 from the sensor const INTERNAL_BITS: RangeInclusive<usize> = 4..=15; /// The bit that indicates a short-to-vcc fault when reading the second u16 from the sensor const FAULT_VCC_SHORT_BIT: usize = 2; /// The bit that indicates a short-to-gnd fault when reading the second u16 from the sensor const FAULT_GROUND_SHORT_BIT: usize = 1; /// The bit that indicates a missing thermocouple fault when reading the second u16 from the sensor const FAULT_NO_THERMOCOUPLE_BIT: usize = 0; /// Possible errors returned by this crate #[derive(Debug)] pub enum Error<SpiE, CsE> { /// An error returned by a call to Transfer::transfer SpiError(SpiE), /// An error returned by a call to OutputPin::{set_high, set_low} ChipSelectError(CsE), /// The fault bit (16) was set in the response from the MAX31855 Fault, /// The SCV fault bit (2) was set in the response from the MAX31855 VccShortFault, /// The SCG fault bit (1) was set in the response from the MAX31855 GroundShortFault, /// The OC fault bit (0) was set in the response from the MAX31855 MissingThermocoupleFault, } /// The temperature unit to use #[derive(Clone, Copy, Debug)] pub enum Unit { /// Degrees Celsius Celsius, /// Degrees Fahrenheit Fahrenheit, /// Degrees Kelvin Kelvin, } impl Unit { /// Converts degrees celsius into this unit pub fn convert(&self, celsius: f32) -> f32 { match self { Unit::Celsius => celsius, Unit::Fahrenheit => celsius * 1.8 + 32., Unit::Kelvin => celsius + 273.15, } } } /// Possible MAX31855 readings pub enum Reading { /// The attached thermocouple Thermocouple, /// The internal reference junction Internal, } impl Reading { /// Convert the raw ADC count into degrees celsius pub fn convert(self, count: i16) -> f32 { let count = count as f32; match self { Reading::Thermocouple => count * 0.25, Reading::Internal => count * 0.0625, } } } enum CsState { High, Low, } use CsState::*; fn set_cs<CS, SpiE, CsE>(cs: &mut CS, state: CsState) -> Result<(), Error<SpiE, CsE>> where CS: OutputPin<Error = CsE>, { let result = match state { CsState::High => cs.set_high(), CsState::Low => cs.set_low(), }; result.map_err(|e| Error::ChipSelectError(e)) } fn transfer<CS, SPI, SpiE, CsE>(spi: &mut SPI, chip_select: &mut CS, buffer: &mut [u8]) -> Result<(), Error<SpiE, CsE>> where CS: OutputPin<Error = CsE>, SPI: Transfer<u8, Error = SpiE>, { set_cs(chip_select, Low)?; spi.transfer(buffer).map_err(|e| Error::SpiError(e))?; set_cs(chip_select, High) } fn bits_to_i16(bits: u16, len: usize, divisor: i16, shift: usize) -> i16 { let negative = bits.get_bit(len - 1); if negative { (bits << shift) as i16 / divisor } else { bits as i16 } } /// Represents the data contained in a full 32-bit read from the MAX31855 as raw ADC counts #[derive(Debug)] pub struct FullResultRaw { /// The temperature of the thermocouple as raw ADC counts pub thermocouple: i16, /// The temperature of the MAX31855 reference junction as raw ADC counts pub internal: i16, } impl FullResultRaw { /// Convert the raw ADC counts into degrees in the provided Unit pub fn convert(self, unit: Unit) -> FullResult { let thermocouple = unit.convert(Reading::Thermocouple.convert(self.thermocouple)); let internal = unit.convert(Reading::Internal.convert(self.internal)); FullResult { thermocouple, internal, unit, } } } /// Represents the data contained in a full 32-bit read from the MAX31855 as degrees in the included Unit #[derive(Debug)] pub struct FullResult { /// The temperature of the thermocouple pub thermocouple: f32, /// The temperature of the MAX31855 reference junction pub internal: f32, /// The unit that the temperatures are in pub unit: Unit, } /// Trait enabling using the MAX31855 pub trait Max31855<SpiE, CsE, CS> { /// Reads the thermocouple temperature and leave it as a raw ADC count. Checks if there is a fault but doesn't detect what kind of fault it is fn read_thermocouple_raw(&mut self, chip_select: &mut CS) -> Result<i16, Error<SpiE, CsE>>; /// Reads the thermocouple temperature and converts it into degrees in the provided unit. Checks if there is a fault but doesn't detect what kind of fault it is fn read_thermocouple(&mut self, chip_select: &mut CS, unit: Unit) -> Result<f32, Error<SpiE, CsE>>; /// Reads both the thermocouple and the internal temperatures, leaving them as raw ADC counts and resolves faults to one of vcc short, ground short or missing thermocouple fn read_all_raw(&mut self, chip_select: &mut CS) -> Result<FullResultRaw, Error<SpiE, CsE>>; /// Reads both the thermocouple and the internal temperatures, converts them into degrees in the provided unit and resolves faults to one of vcc short, ground short or missing thermocouple fn read_all(&mut self, chip_select: &mut CS, unit: Unit) -> Result<FullResult, Error<SpiE, CsE>>; } impl<CS, SPI, SpiE, CsE> Max31855<SpiE, CsE, CS> for SPI where CS: OutputPin<Error = CsE>, SPI: Transfer<u8, Error = SpiE>, { /// Reads the thermocouple temperature and leave it as a raw ADC count. Checks if there is a fault but doesn't detect what kind of fault it is fn read_thermocouple_raw(&mut self, chip_select: &mut CS) -> Result<i16, Error<SpiE, CsE>> { let mut buffer = [0; 2]; transfer(self, chip_select, &mut buffer)?; if buffer[1].get_bit(FAULT_BIT) { Err(Error::Fault)? } let raw = (buffer[0] as u16) << 8 | (buffer[1] as u16) << 0; let thermocouple = bits_to_i16(raw.get_bits(THERMOCOUPLE_BITS), 14, 4, 2); Ok(thermocouple) } /// Reads the thermocouple temperature and converts it into degrees in the provided unit. Checks if there is a fault but doesn't detect what kind of fault it is fn read_thermocouple(&mut self, chip_select: &mut CS, unit: Unit) -> Result<f32, Error<SpiE, CsE>> { self .read_thermocouple_raw(chip_select) .map(|r| unit.convert(Reading::Thermocouple.convert(r))) } /// Reads both the thermocouple and the internal temperatures, leaving them as raw ADC counts and resolves faults to one of vcc short, ground short or missing thermocouple fn read_all_raw(&mut self, chip_select: &mut CS) -> Result<FullResultRaw, Error<SpiE, CsE>> { let mut buffer = [0; 4]; transfer(self, chip_select, &mut buffer)?; let fault = buffer[1].get_bit(0); if fault { let raw = (buffer[2] as u16) << 8 | (buffer[3] as u16) << 0; if raw.get_bit(FAULT_NO_THERMOCOUPLE_BIT) { Err(Error::MissingThermocoupleFault)? } else if raw.get_bit(FAULT_GROUND_SHORT_BIT) { Err(Error::GroundShortFault)? } else if raw.get_bit(FAULT_VCC_SHORT_BIT) { Err(Error::VccShortFault)? } else { // This should impossible, one of the other fields should be set as well // but handled here just-in-case Err(Error::Fault)? } } let first_u16 = (buffer[0] as u16) << 8 | (buffer[1] as u16) << 0; let second_u16 = (buffer[2] as u16) << 8 | (buffer[3] as u16) << 0; let thermocouple = bits_to_i16(first_u16.get_bits(THERMOCOUPLE_BITS), 14, 4, 2); let internal = bits_to_i16(second_u16.get_bits(INTERNAL_BITS), 12, 16, 4); Ok(FullResultRaw { thermocouple, internal, }) } /// Reads both the thermocouple and the internal temperatures, converts them into degrees in the provided unit and resolves faults to one of vcc short, ground short or missing thermocouple fn read_all(&mut self, chip_select: &mut CS, unit: Unit) -> Result<FullResult, Error<SpiE, CsE>> { self .read_all_raw(chip_select) .map(|r| r.convert(unit)) } }