Raspberry Pi Tutorial Series: 1-Wire DS18B20 Sensor

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DS18B20 is a common temperature sensor which communicates over a 1-Wire bus that by definition requires only one data line. Usually, a certain MCU reads data from DS18B20 in strict accordance with Timing, but now we are going to control DS18B20 using a Raspberry and with the Raspbian OS. You will find that everything is file in the Linux.

Enable 1-Wire

Enable 1-Wire interface with the raspi-config tool.

sudo raspi-config

Select Advanced Option -> 1-Wire -> <Yes>

In fact this tool edits the /boot/config.txt and appends this line: dtoverlay=w1-gpio. With this line, a GPIO to drive an external pullup is disabled by default. It's inconvenience in certain condition so we often change "dtoverlay=w1-gpio" to "dtoverlay=w1-gpio-pullup". We also specify GPIO 4 for I/O, so we change the line to "dtoverlay=w1-gpio-pullup,gpiopin=4". Just for instance, because GPIO 4 is used for I/O by default so "gpiopin=4" is not usually required.

More details about "dtoverlay", please read the manual: /boot/overlays/README.

  • Quote from /boot/overlays/README:
Name:   w1-gpio
Info:   Configures the w1-gpio Onewire interface module.
        Use this overlay if you *don't* need a GPIO to drive an external pullup.
Load:   dtoverlay=w1-gpio,<param>=<val>
Params: gpiopin                 GPIO for I/O (default "4")

        pullup                  Non-zero, "on", or "y" to enable the parasitic
                                power (2-wire, power-on-data) feature


Name:   w1-gpio-pullup
Info:   Configures the w1-gpio Onewire interface module.
        Use this overlay if you *do* need a GPIO to drive an external pullup.
Load:   dtoverlay=w1-gpio-pullup,<param>=<val>
Params: gpiopin                 GPIO for I/O (default "4")

        pullup                  Non-zero, "on", or "y" to enable the parasitic
                                power (2-wire, power-on-data) feature

        extpullup               GPIO for external pullup (default "5")

Finally, we append this line to the config.txt file: "dtoverlay=w1-gpio-pullup,gpiopin=4" (no space in this line).