Controller Circuit for Digital Temperature Sensor

The project aims to build a digital sensor thermometer based on TMP275which is 0.5°C accurate and uses 2-wire interface to connect to a microcontroller.

The TMP275 is a serial output temperature sensor that is capable of reading temperatures with a resolution of 0.0625°C. It allows up to 8 devices on a single bus since it is SMBus-compatible. For extended temperature measurement in a variety of communication, instrumentation, industrial, consumer, and computer applications, the TMP275 is suitable.

The data from the sensor is read by an ATmega8 microcontroller and uses a 4-digit 7-segment LED indicator as display. In order to be powered from a standard 9V battery, an onboard 7805 voltage regulator is available. The use of I2C interface is the easiest way to get the temperature out of the TMP275. To limit the current draw on the pins of ATmega8, PNP transistors on the common anodes and resistors on the segments are used.

A bypass capacitor between VCC and GND and two pull-up resistors required on SDA and SCL lines are the only external components needed by the TMP275. A display macro had to be written which figures how data is displayed.

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