The LM75 sensor Figure 1 used for this project is only available as an S08 8-pin package with short pins. The BH digital light sensor can be used to provide information to the Raspberry Pi about ambient light levels. The temperature sensor in this project Figure 2 acts as a regulator for a fan. Board Setup and Configuration. With a few Arduino sensors and a little programming, you can take the guesswork out of watering your plants. The microcontroller would then send another start signal.

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A small test using the i2cdetect command shows whether everything works properly Listing 1. These will be published when they are tested. This is where bitwise operations are handy! Related Hardware and Initiatives. To get the temperature km75 degree Celsius, we need to divide this number bymaking sure the output is a floating point number.

The value in the high-order byte indicates that an additional 0.

Transforming data buffers into floating point temperature, and vice-versa, is a tricky task. We encourage you to use the method explained above using the bit integer to record and display temperature data. Please glance through it, and make sure to have it visible while reading this page.

Arduino Playground – LM75

In this tutorial, we assume that the device is connected and returns already a meaningful temperature, as introduced in the ml75 section. Moreover, you should note that the factory setting for lk75 output is “low active” and the output handles a maximum of 10mA.


The LM75 has four internal registers Table 1. The programmable output port of the LM75 digital temperature sensor teams up with a Raspberry Pi to form a temperature monitoring system. Therefore, you will need to make sure that the current flow is minimal. The conversion code therefore becomes:. Initial release July This sensor uses the I2C bus protocol to communicate allowing the Arduino standard Wire library to communicate with the device.

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This digital sensor has a programmable output port that you can use to build simple systems for monitoring temperatures. Getting your first temperature measurements. A byte array l,75 the right size is therefore needed. Note that the mbed code creates the string array lk75 by digit rather than using the printf function. A surface-mount device SMD is a circuit board with a high density of components achieved by soldering the components directly onto the board.

Getting your lm57 temperature measurements We will provide more details about how the device is configured, linking the code with the relevant sections of the datasheet. All interactions with the device involve writing and reading the content of these registers, so this is what we will look at next.

You will recognise similar operations to transform the buffer into a number. People speak of outdoor temperatures in terms of wind chill, heat index, and other perceived values, but Raspberry Pi fans can get hard facts about temperature with temperature sensors and a little program logic.


The addresses begin with 0x48h and ends at 0x4Fh.

I2C Temperature Sensors derived from the LM75

Keep Your Cool Martin Mohr. These 11 bits represents the whole temperature range, with a 0.

The configuration register controls the different modes of operation of the device; you can read or write on it, although you would most write on it to set the desired behaviour of the sensor.

As part of the ongoing series of articles on the I2C bus, in this article I address the LM75 temperature sensor. However, to read data, we need two steps, one to indicate, with a write command which register we want to read, followed by a read. For more info pleae look at this Forum Post. Each register has an address. This would set the l7m5 of the configuration buffer:.

Every milliampere creates additional heat, which could potentially affect the validity of the measurements. When the values rise above a certain level, the sensor switches the fan k2c, which then runs until the temperature falls back below the level that caused the sensor to trigger it to begin with.