diff --git a/src/shared/sensors/MAX31855/MAX31855.h b/src/shared/sensors/MAX31855/MAX31855.h
index 2c5fb8067b12eec4bf015539d34927ffd6fa8a45..62be42ab10eabb7c66a507c9d67449cbc92eec01 100644
--- a/src/shared/sensors/MAX31855/MAX31855.h
+++ b/src/shared/sensors/MAX31855/MAX31855.h
@@ -29,6 +29,17 @@
namespace Boardcore
{
+/**
+ * @brief MAX31855 thermocouple sensor driver.
+ *
+ * The MAX31855 performs cold-junction compensation and digitizes the signal
+ * from a K, J, N, T, S, R, or E type thermocouple depending on the selected
+ * product variant. The data is output in a signed 14-bit, SPI-compatible,
+ * read-only format. This converter resolves temperatures to 0.25°C, allows
+ * readings as high as +1800°C and as low as -270°C, and exhibits thermocouple
+ * accuracy of ±2°C for temperatures ranging from -200°C to +700°C for K-type
+ * thermocouples.
+ */
class MAX31855 : public Sensor<TemperatureData>
{
public:
diff --git a/src/shared/sensors/MAX31856/MAX31856.cpp b/src/shared/sensors/MAX31856/MAX31856.cpp
index 325e1ac8aaad44ce19d95db2c63db613fc5e8d80..ad1d5475980f62eea2eb31e4df99e49778081b53 100644
--- a/src/shared/sensors/MAX31856/MAX31856.cpp
+++ b/src/shared/sensors/MAX31856/MAX31856.cpp
@@ -49,6 +49,9 @@ bool MAX31856::init()
// Set thermocouple type
setThermocoupleType(type);
+ // Reset the cold junction offset
+ setColdJunctionOffset(0);
+
// Enable continuous conversion mode
spi.writeRegister(CR0, CR0_CMODE);
@@ -81,46 +84,44 @@ void MAX31856::setThermocoupleType(ThermocoupleType type)
spi.writeRegister(CR1, static_cast<uint8_t>(type));
}
-TemperatureData MAX31856::sampleImpl()
+void MAX31856::setColdJunctionOffset(float offset)
{
- int32_t sample;
+ SPITransaction spi{slave};
+ spi.writeRegister(CJTO,
+ static_cast<int8_t>(offset * 1 / CJ_TEMP_LSB_VALUE));
+}
- {
- SPITransaction spi{slave};
- sample = spi.readRegister24(LTCBH);
- }
+MAX31856Data MAX31856::sampleImpl()
+{
+ SPITransaction spi{slave};
+ int16_t cjRaw = spi.readRegister16(CJTH);
+ int32_t tcRaw = spi.readRegister24(LTCBH);
- TemperatureData result{};
+ MAX31856Data result;
result.temperatureTimestamp = TimestampTimer::getTimestamp();
- // Sign extension
- sample = sample << 8;
- sample = sample >> (8 + 5);
-
- // Convert the integer and decimal part separately
- result.temperature = static_cast<float>(sample) * 0.007812;
+ // The register has:
+ // - A leading sign bit (which is actually two's complement)
+ // - The other 18 bits
+ // - 5 unused trailing bits
- return result;
-}
-
-TemperatureData MAX31856::readInternalTemperature()
-{
- uint16_t sample[2];
-
- {
- SPITransaction spi{slave};
- spi.read16(sample, sizeof(sample));
- }
+ // Since the 24 bit registers value is stored into a 32 bit variable, first
+ // we make a left shift to move the sign bit in the 31st bit, and then a
+ // right shift to remove the unused bits.
+ // This automatically extends the sign
+ tcRaw = tcRaw << 8;
+ tcRaw = tcRaw >> (8 + 5);
- TemperatureData result{};
- result.temperatureTimestamp = TimestampTimer::getTimestamp();
+ // Here we just make a right shift as the sign bit is already in the 15th
+ // bit. This will also perform the sign extension like in sampleImpl()
+ cjRaw = cjRaw >> 4;
- // Extract data bits
- sample[1] = sample[1] >> 4;
+ // Convert the raw value into temperature
+ result.temperature = static_cast<float>(tcRaw) * TC_TEMP_LSB_VALUE;
- // Convert the integer and decimal part separately
- result.temperature = static_cast<float>(sample[1] >> 4);
- result.temperature += static_cast<float>(sample[1] & 0xF) * 0.0625;
+ // Convert the raw value into temperature
+ result.coldJunctionTemperature =
+ static_cast<float>(cjRaw) * CJ_TEMP_LSB_VALUE;
return result;
}
diff --git a/src/shared/sensors/MAX31856/MAX31856.h b/src/shared/sensors/MAX31856/MAX31856.h
index 97fbd817e8eb3e13766eaea09c847c644a836c4a..7e04e481a5b820ccc2fb37597419cea2b341394a 100644
--- a/src/shared/sensors/MAX31856/MAX31856.h
+++ b/src/shared/sensors/MAX31856/MAX31856.h
@@ -26,10 +26,25 @@
#include <drivers/spi/SPIDriver.h>
#include <sensors/Sensor.h>
+#include "MAX31856Data.h"
+
namespace Boardcore
{
-class MAX31856 : public Sensor<TemperatureData>
+/**
+ * @brief MAX31855 thermocouple sensor driver.
+ *
+ * The MAX31856 performs cold-junction compensation and digitizes the signal
+ * from any type of thermocouple. This converter resolves temperatures to
+ * 0.0078125°C, allows readings as high as +1800°C and as low as -210°C
+ * (depending on thermocouple type), and exhibits thermocouple voltage
+ * measurement accuracy of ±0.15%. The thermocouple inputs are protected against
+ * over voltage conditions up to ±45V. A lookup table (LUT) stores linearity
+ * correction data for several types of thermocouples (K, J, N, R, S, T, E, and
+ * B). Line frequency filtering of 50Hz and 60Hz is included, as is thermocouple
+ * fault detection
+ */
+class MAX31856 : public Sensor<MAX31856Data>
{
public:
enum class ThermocoupleType : uint8_t
@@ -63,13 +78,10 @@ public:
void setThermocoupleType(ThermocoupleType type);
- /**
- * @brief Read the device internal temperature (cold junction).
- */
- TemperatureData readInternalTemperature();
+ void setColdJunctionOffset(float offset);
private:
- TemperatureData sampleImpl() override;
+ MAX31856Data sampleImpl() override;
SPISlave slave;
ThermocoupleType type;
@@ -99,6 +111,9 @@ private:
static constexpr uint8_t CR0_CMODE = 0x1 << 7;
static constexpr uint8_t CR0_OCFAULT_0 = 0x1 << 4;
static constexpr uint8_t SR_OPEN = 0x1 << 0;
+
+ static constexpr float TC_TEMP_LSB_VALUE = 0.007812; // [°C]
+ static constexpr float CJ_TEMP_LSB_VALUE = 0.0625; // [°C]
};
} // namespace Boardcore
diff --git a/src/shared/sensors/MAX31856/MAX31856Data.h b/src/shared/sensors/MAX31856/MAX31856Data.h
new file mode 100644
index 0000000000000000000000000000000000000000..ebd5742eb02c1a6d117ec4e061d08187b4141a0f
--- /dev/null
+++ b/src/shared/sensors/MAX31856/MAX31856Data.h
@@ -0,0 +1,65 @@
+/* Copyright (c) 2023 Skyward Experimental Rocketry
+ * Author: Alberto Nidasio
+ *
+ * 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 <utils/Debug.h>
+
+#include <cstdio>
+#include <map>
+
+#include "sensors/SensorData.h"
+
+namespace Boardcore
+{
+
+struct MAX31856Data : public TemperatureData
+{
+ float coldJunctionTemperature;
+
+ MAX31856Data() : MAX31856Data{0, 0.0, 0.0} {}
+
+ MAX31856Data(uint64_t temperatureTimestamp, float temperature)
+ : MAX31856Data(temperatureTimestamp, temperature, 0)
+ {
+ }
+
+ MAX31856Data(uint64_t temperatureTimestamp, float temperature,
+ float coldJunctionTemperature)
+ : TemperatureData{temperatureTimestamp, temperature},
+ coldJunctionTemperature(coldJunctionTemperature)
+ {
+ }
+
+ static std::string header()
+ {
+ return "temperatureTimestamp,temperature,coldJunctionTemperature\n";
+ }
+
+ void print(std::ostream& os) const
+ {
+ os << temperatureTimestamp << "," << temperature << ","
+ << coldJunctionTemperature << "\n";
+ }
+};
+
+} // namespace Boardcore
\ No newline at end of file
diff --git a/src/tests/sensors/test-max31856.cpp b/src/tests/sensors/test-max31856.cpp
index 8cf44008d1929c29f87cdfbb14ca5f131fc5fb58..6d4a3edd655e93480c365ce5f258f72d7be9fa82 100644
--- a/src/tests/sensors/test-max31856.cpp
+++ b/src/tests/sensors/test-max31856.cpp
@@ -60,13 +60,23 @@ int main()
printf("The thermocouple is connected\n");
}
+ // Wait for one sample to be made
+ Thread::sleep(100);
+
+ // Set cold junction offset
+ // This should set the cold junction temperature to 25°
+ sensor.sample();
+ auto sample = sensor.getLastSample();
+ sensor.setColdJunctionOffset(sample.coldJunctionTemperature - 25);
+ printf("Offset: %f\n", sample.coldJunctionTemperature - 25);
+
while (true)
{
sensor.sample();
- TemperatureData sample = sensor.getLastSample();
+ sample = sensor.getLastSample();
- printf("\r\e[0K[%.2f] %.2f", sample.temperatureTimestamp / 1e6,
- sample.temperature);
+ printf("[%.2f] %f %f\n", sample.temperatureTimestamp / 1e6,
+ sample.temperature, sample.coldJunctionTemperature);
Thread::sleep(100);
}