{"id":3146,"date":"2011-07-17T14:48:53","date_gmt":"2011-07-17T18:48:53","guid":{"rendered":"http:\/\/embedded-lab.com\/blog\/?p=3146"},"modified":"2012-11-06T14:00:32","modified_gmt":"2012-11-06T19:00:32","slug":"using-tc74-microchip-thermal-sensor-for-temperature-measurement","status":"publish","type":"post","link":"https:\/\/embedded-lab.com\/blog\/using-tc74-microchip-thermal-sensor-for-temperature-measurement\/","title":{"rendered":"Using TC74 (Microchip) thermal sensor for temperature measurement"},"content":{"rendered":"

The TC74 chip is a serially accessible, digital temperature\u00a0sensor from Microchip Technology that acquires and converts temperature information from its onboard solid-state sensor with a resolution of 1\u00b0C. The temperature is available as an 8-bit digital word stored in its internal temperature register, which is accessible through a 2-wire I2C compatible serial bus. This tutorial describes how to use the TC74 sensor with a PIC microcontroller to measure the surrounding temperature.<\/p>\n

\"\"<\/a>

Using TC74 sensor for temperature measurement<\/p><\/div>\n

<\/p>\n

Theory<\/strong><\/p>\n

The TC74 digital temperature sensor is available in\u00a0SOT-23 and\u00a0TO-220 packages. The communication with the device is accomplished via a 2-wire I2C compatible serial bus.\u00a0Temperature resolution is 1\u00b0C and conversion rate is a\u00a0nominal 8 samples\/sec. The pin diagram of TC74 chip is shown below for reference.<\/p>\n

\"\"<\/a>

Pin diagram of TC74<\/p><\/div>\n

The TC74 stores the measured temperature into its 8-bit internal register as 2’s complement binary format. The most significant bit is the sign bit, which is set to 1 for negative temperatures. Therefore, the maximum measurable positive temperature is + 127\u00a0\u00b0C (0111 1111). The TC74 has also got another 8-bit Read\/Write Configuration Register (RWCR) that is used to\u00a0put the device into a low\u00a0power (IDD<\/sub> = 5 \u00b5A, typical) Standby mode. In this\u00a0mode, the A\/D converter is halted and the temperature\u00a0data registers are frozen. Bit 7 of RWCR must be set to put TC74 into Standby mode.<\/p>\n

\"\"<\/a>

Temperature conversion table and internal registers<\/p><\/div>\n

Serial port operation<\/em><\/strong><\/p>\n

The Serial Clock input (SCLK) and bidirectional data\u00a0port (SDA) form a 2-wire bidirectional serial port for communicating with the TC74. The port is I2C compatible and all transfers take place under the control of a host, usually a microcontroller. The host microcontroller provides the clock signal for all the data transfers and the TC74\u00a0always operates as a Slave. The default 7-bit I2C address of TC74 is 1001 101b. However, 7 other address options are also available which can be identified from the part number of the device. For example, I have got a TC74A0 in TO-220 package. A0 corresponds to the device address 1001 000b. Similarly, TC74A3 has its I2C address 1001 011b. Refer the datasheet<\/a><\/strong> for further details. If you are not familiar with I2C protocol, please read my article, Inter-Integrated Circuit (I2C) communication in PIC<\/a><\/strong>. Reading temperature from a TC74 device through I2C port involves the following steps:<\/p>\n