/** * Copyright (c) 2020 Raspberry Pi (Trading) Ltd. * * SPDX-License-Identifier: BSD-3-Clause */ #include <stdio.h> #include <string.h> #include "pico/stdlib.h" #include "pico/binary_info.h" #include "hardware/i2c.h" /* Example code to talk to a MCP9808 ±0.5°C Digital temperature Sensor This reads and writes to registers on the board. Connections on Raspberry Pi Pico board, other boards may vary. GPIO PICO_DEFAULT_I2C_SDA_PIN (On Pico this is GP4 (physical pin 6)) -> SDA on MCP9808 board GPIO PICO_DEFAULT_I2C_SCK_PIN (On Pico this is GP5 (physical pin 7)) -> SCL on MCP9808 board Vsys (physical pin 39) -> VDD on MCP9808 board GND (physical pin 38) -> GND on MCP9808 board */ //The bus address is determined by the state of pins A0, A1 and A2 on the MCP9808 board static uint8_t ADDRESS = 0x18; //hardware registers const uint8_t REG_POINTER = 0x00; const uint8_t REG_CONFIG = 0x01; const uint8_t REG_TEMP_UPPER = 0x02; const uint8_t REG_TEMP_LOWER = 0x03; const uint8_t REG_TEMP_CRIT = 0x04; const uint8_t REG_TEMP_AMB = 0x05; const uint8_t REG_RESOLUTION = 0x08; void mcp9808_check_limits(uint8_t upper_byte) { // Check flags and raise alerts accordingly if ((upper_byte & 0x40) == 0x40) { //TA > TUPPER printf("Temperature is above the upper temperature limit.\n"); } if ((upper_byte & 0x20) == 0x20) { //TA < TLOWER printf("Temperature is below the lower temperature limit.\n"); } if ((upper_byte & 0x80) == 0x80) { //TA > TCRIT printf("Temperature is above the critical temperature limit.\n"); } } float mcp9808_convert_temp(uint8_t upper_byte, uint8_t lower_byte) { float temperature; //Check if TA <= 0°C and convert to denary accordingly if ((upper_byte & 0x10) == 0x10) { upper_byte = upper_byte & 0x0F; temperature = 256 - (((float) upper_byte * 16) + ((float) lower_byte / 16)); } else { temperature = (((float) upper_byte * 16) + ((float) lower_byte / 16)); } return temperature; } #ifdef i2c_default void mcp9808_set_limits() { //Set an upper limit of 30°C for the temperature uint8_t upper_temp_msb = 0x01; uint8_t upper_temp_lsb = 0xE0; //Set a lower limit of 20°C for the temperature uint8_t lower_temp_msb = 0x01; uint8_t lower_temp_lsb = 0x40; //Set a critical limit of 40°C for the temperature uint8_t crit_temp_msb = 0x02; uint8_t crit_temp_lsb = 0x80; uint8_t buf[3]; buf[0] = REG_TEMP_UPPER; buf[1] = upper_temp_msb; buf[2] = upper_temp_lsb; i2c_write_blocking(i2c_default, ADDRESS, buf, 3, false); buf[0] = REG_TEMP_LOWER; buf[1] = lower_temp_msb; buf[2] = lower_temp_lsb; i2c_write_blocking(i2c_default, ADDRESS, buf, 3, false); buf[0] = REG_TEMP_CRIT; buf[1] = crit_temp_msb; buf[2] = crit_temp_lsb;; i2c_write_blocking(i2c_default, ADDRESS, buf, 3, false); } #endif int main() { stdio_init_all(); #if !defined(i2c_default) || !defined(PICO_DEFAULT_I2C_SDA_PIN) || !defined(PICO_DEFAULT_I2C_SCL_PIN) #warning i2c/mcp9808_i2c example requires a board with I2C pins puts("Default I2C pins were not defined"); #else printf("Hello, MCP9808! Reading raw data from registers...\n"); // This example will use I2C0 on the default SDA and SCL pins (4, 5 on a Pico) i2c_init(i2c_default, 400 * 1000); gpio_set_function(PICO_DEFAULT_I2C_SDA_PIN, GPIO_FUNC_I2C); gpio_set_function(PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C); gpio_pull_up(PICO_DEFAULT_I2C_SDA_PIN); gpio_pull_up(PICO_DEFAULT_I2C_SCL_PIN); // Make the I2C pins available to picotool bi_decl(bi_2pins_with_func(PICO_DEFAULT_I2C_SDA_PIN, PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C)); mcp9808_set_limits(); uint8_t buf[2]; uint16_t upper_byte; uint16_t lower_byte; float temperature; while (1) { // Start reading ambient temperature register for 2 bytes i2c_write_blocking(i2c_default, ADDRESS, &REG_TEMP_AMB, 1, true); i2c_read_blocking(i2c_default, ADDRESS, buf, 2, false); upper_byte = buf[0]; lower_byte = buf[1]; //isolates limit flags in upper byte mcp9808_check_limits(upper_byte & 0xE0); //clears flag bits in upper byte temperature = mcp9808_convert_temp(upper_byte & 0x1F, lower_byte); printf("Ambient temperature: %.4f°C\n", temperature); sleep_ms(1000); } #endif }

This firmware image was imported from the pico-examples repository. 


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