Library for MAX31855/MAX6675 from Maxim Integrated for STM32
As I needed to measure higher temperature and especially negative ones, I decided to use MAX31855 instead of MAX6675 in my new project. I updated the repo and added the library for MAX31855 too. Also, I uploaded a breakout board for MAX31855 and an example code in stm32cubeIDE.
For sensing a temperature in my hot air gun nozzle, I had to use an amplifier circuit to amplify output signal of a thermocouple. As you probably know, MAX6675 is an all-in-one Integrated circuit that provides a digital output from thermocouple input. As a result, you can save some components and space on your PCB. According to ‘Datasheet’, The MAX6675 performs cold-junction compensation and digitizes the signal from a type-K thermocouple. The data is output in a 12-bit resolution, SPI compatible, read-only format. I wrote a simple library that you can use to get the temperature from MAX6675. I used STM32F030F4P6. However, you can port it to other microcontrollers. I also provided a complete project in STM32CubeIDE that you can use as a reference. You can run code and see data in STMStudio.
1- Activate SPI from STM32CubeMX. As I mentioned before, this chip is read-only, so that you can configure your microcontroller as a receive-only master. Also, the length of data is 16bit and MSB First. Use one of the GPIO’s as a Slave Select(SS). I used first pin from GPIOB (GPIOB_PIN_1).
2-Add my library to your compiler and in MAX6675.h set the SS port and pin that you activated in STM32cubeMX. The output of Max6675_Read_Temp is the temperature in centigrade
#define SSPORT GPIOB // GPIO Port of Chip Select(Slave Select)
#define SSPIN GPIO_PIN_1 // GPIO PIN of Chip Select(Slave Select)You can see the test results of this chip. I put thermocouple in the ice to plot the temperature change. TS is connection flag. If you disconnect thermocouple from the chip, it goes high.
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