pico-ds18b20

Raspberry Pi Pico C++ library for the ds18b20 temperature sensor

How to connect

Note: Does not support parasite power mode

You first need to determine whether your ds18b20 has a built-in pull-up resistor or not. ds18b20's with built-in pull-up resistors usually have a small component connected across all three wires (ex. Keystudio ds18b20).

Without built-in pull-up resistor

With built-in pull-up resistor

In case your ds18b20 doesn't have a built-in pull-up resistor, you need to connect one $4.7k\Omega$ resistor across VDD and DQ yourself.

Connect:

• VDD: to 5V (ex. VBUS pin) or 3.3V (ex. 3V3 pin)
• GND: to ground (any GND pin)
• DQ: to any GPIO pin

For example:

Without built-in pull-up resistor

With built-in pull-up resistor

How to run

• Download the Embedded Temple Library (ETL) and copy the include folder to the root of this project
• Compile

  ninja -C /home/panagiotis/pico_projects/pico-ds18b20/build

• Set the Raspberry Pi Pico in bootloader mode by connecting it through USB while pressing its button
• Load build/ds18b20.elf to Raspberry Pi Pico

How to use

See the examples folder for complete programs

Find all the ds18b20 devices connected to GPIO 0

#include "one_wire.hpp"
#include "ds18b20.hpp"

OneWire one_wire(0);

// Find all devices at pin 0
etl::vector<Ds18b20, 10> devices = Ds18b20::find_devices(one_wire);

// Check if they are successfully initialized
for (int i = 0; i < devices.size(); i++) {
    if (!devices[i].is_successfully_initialized()) {
        printf("Could not initialize device index %d. Do not use!\n", i);
    }
}

// Select device index i
Ds18b20& device = devices[i];
// ...

Measure and print the temperature of a device

std::optional<float> result = device.measure_temperature();
if (result.has_value()) {
    float temperature = result.value();
    printf("%f\n", temperature);
} else {
    printf("Could not calculate temperature\n");
}

Set resolution

bool success = device.set_resolution(Resolution::VeryHigh, true);
if (!success) {
    printf("Could not set resolution\n");
}

Set the low/high alarm temperature range values

bool success0 = device.set_temperature_low_limit(-20, true);
bool success1 = device.set_temperature_high_limit(80, true);
if (!success0 || !success1) {
    printf("Could not set temperature limits\n");
}

Detect temperature alarms after temperature measurements

std::optional<float> result = device.measure_temperature();
if (result.has_value()) {
    if (device.is_alarm_active()) {
        printf("ALARM!!!\n");
    } else {
        printf("All safe!\n");
    }
}

Check if a device is operational

// ...

bool is_operational = device.ping();
if (is_operational) {
    printf("Fully operational!\n");
} else {
    printf("Device not operating correctly\n");
}

Features

• Measure temperature
  • ±0.5°C from -10°C to +85°C
  • ±1°C from -30°C to +100°C
  • ±2°C from -55°C to +125°C
• Set resolution (temperature discrete step size)
  • Low: 0.0625°C steps
  • Medium: 0.125°C steps
  • High: 0.25°C steps
  • Very High: 0.5°C steps
• Detect alarm when temperature goes out of bounds
• Set the low and high bounds of the temperature alarm range
  • The range is [-128, 127] as integers
• Check if a device is operational
• Fetch the power mode of the device (external or parasite)

Resources

• ds18b20 Analog datasheet
• Book of iButton® Standards
• Application Note 187 | 1-Wire Search Algorithm