sensor_mlx90614: add library to read from MLX90614 IR-thermometer

lib/sensor_mlx90614.c

@@ -0,0 +1,86 @@
+/** library to communicate with MLX90614 infra-red thermometer
+ *  @file
+ *  @author King Kévin <kingkevin@cuvoodoo.info>
+ *  @copyright SPDX-License-Identifier: GPL-3.0-or-later
+ *  @date 2020
+ *  @note peripherals used: GPIO @ref sensor_mlx90614_gpio, I2C @ref i2c_master_i2c
+ *  @note this library only uses the I²C interface, not the PWM output
+ */
+/* standard libraries */
+#include <stdint.h> // standard integer types
+#include <stdbool.h> // boolean type
+#include <stdlib.h> // general utilities
+#include <math.h> // NaN definition
+
+/* STM32 (including CM3) libraries */
+#include <libopencm3/stm32/rcc.h> // real-time control clock library
+#include <libopencm3/stm32/gpio.h> // general purpose input output library
+#include <libopencm3/stm32/i2c.h> // I²C library
+
+/* own libraries */
+#include "global.h" // global utilities
+#include "sensor_mlx90614.h" // own definitions
+#include "smbus_master.h" // SMBus utilities
+
+/** @defgroup sensor_mlx90614_gpio GPIO pin used to control the MLX90614
+ *  @{
+ */
+#define SENSOR_MLX90614_SCL PA8 /**< GPIO pin for SMBus SCL, use to send request condition to switch mode from PWM to SMBus (must be the same as used for SMBus communication) */
+/** @} */
+
+/** MLX90614 I²C slave address */
+static uint8_t sensor_mlx90614_slave_addr = 0x5a;
+
+bool sensor_mlx90614_setup(uint8_t slave_addr)
+{
+	if (!smbus_master_check_signals()) { // check if there are pull-ups to operate I²C
+		return false;
+	}
+
+	// send request condition to switch to I²C mode
+	rcc_periph_clock_enable(GPIO_RCC(SENSOR_MLX90614_SCL)); // enable clock for GPIO port domain
+	gpio_mode_setup(GPIO_PORT(SENSOR_MLX90614_SCL), GPIO_MODE_OUTPUT, GPIO_PUPD_NONE, GPIO_PIN(SENSOR_MLX90614_SCL)); // set pin as output
+	gpio_set_output_options(GPIO_PORT(SENSOR_MLX90614_SCL), GPIO_OTYPE_OD, GPIO_OSPEED_2MHZ, GPIO_PIN(SENSOR_MLX90614_SCL)); // set pin output as open-drain (should be pulled up by external resistors required for I²C communication
+	gpio_clear(GPIO_PORT(SENSOR_MLX90614_SCL), GPIO_PIN(SENSOR_MLX90614_SCL)); // set low to send request condition
+	sleep_us(1024 + 500); // SMBus Request is min. 1.024 ms
+	gpio_set(GPIO_PORT(SENSOR_MLX90614_SCL), GPIO_PIN(SENSOR_MLX90614_SCL)); // set back high to end request condition
+
+	if (slave_addr < 0x80) { // only the least 7-bit are valid (use default address else)
+		sensor_mlx90614_slave_addr = slave_addr; // save I²C slave address of MLX90614
+	}
+	smbus_master_setup(100, true); // setup SMBus with PEC
+	uint8_t response[2]; // response is always 2 bytes
+	// test if the device is present
+	smbus_master_command_read(sensor_mlx90614_slave_addr, 0x20 | 0x0e, response, LENGTH(response)); // I don't know whey, but the PEC for the first transfer is erroneous, maybe because it has some old bits in the calculation buffer
+	const enum smbus_master_rc rc = smbus_master_command_read(sensor_mlx90614_slave_addr, 0x20 | 0x0e, response, LENGTH(response)); // read its own slave address
+	if (SMBUS_MASTER_RC_NONE != rc) { // read failed
+		return false; // could not read from SMBus device
+	}
+	
+	if (sensor_mlx90614_slave_addr != response[0]) { // the used slave address does not match the one in the ROM
+		return false; // this is probably not a MLX90614
+	}
+	return true;
+}
+
+float sensor_mlx90614_temperature_ambient(void)
+{
+	uint8_t response[2]; // response is always 2 bytes
+	const enum smbus_master_rc rc = smbus_master_command_read(sensor_mlx90614_slave_addr, 0x00 | 0x06, response, LENGTH(response)); // read Ta from RAM
+	if (SMBUS_MASTER_RC_NONE != rc) { // read failed
+		return NAN;
+	}
+	const uint16_t temp = response[0] + (response[1] << 8); // low byte is transferred first
+	return temp * 0.02 - 273.15; // calculated temperature according to specification 7.7.1
+}
+
+float sensor_mlx90614_temperature_object(void)
+{
+	uint8_t response[2]; // response is always 2 bytes
+	const enum smbus_master_rc rc = smbus_master_command_read(sensor_mlx90614_slave_addr, 0x00 | 0x07, response, LENGTH(response)); // read Tobj1 from RAM
+	if (SMBUS_MASTER_RC_NONE != rc) { // read failed
+		return NAN;
+	}
+	const uint16_t temp = response[0] + (response[1] << 8); // low byte is transferred first
+	return temp * 0.02 - 273.15; // calculated temperature according to specification 7.7.1
+}

lib/sensor_mlx90614.h

@@ -0,0 +1,27 @@
+/** library to communicate with MLX90614 infra-red thermometer
+ *  @file
+ *  @author King Kévin <kingkevin@cuvoodoo.info>
+ *  @copyright SPDX-License-Identifier: GPL-3.0-or-later
+ *  @date 2020
+ *  @note peripherals used: GPIO @ref sensor_mlx90614_gpio, I2C @ref i2c_master_i2c
+ *  @note this library only uses the I²C interface, not the PWM output
+ */
+#pragma once
+
+/** setup I²C bus to communicated with MLX90614 Infra-Red thermometer
+ *  @param[in] slave_addr I²C slave address of MLX90614 device (least significant 7-bit, 0xff for default)
+ *  @return if the display setup is successful, else the display is probably not on the I²C bus
+ *  @warning only one display on the I²C bus is currently supported
+ *  @note I²C frequency is 100 kHz
+ */
+bool sensor_mlx90614_setup(uint8_t slave_addr);
+/** get ambient temperature of sensor
+ *  @return ambient temperature in °C
+ *  @note uses internal thermistor
+ */
+float sensor_mlx90614_temperature_ambient(void);
+/** get measured object temperature
+ *  @return object temperature in °C
+ *  @note uses IR sensor
+ */
+float sensor_mlx90614_temperature_object(void);