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