Tag Archives: Digital Temperature Meter


Testing active analog temperature sensors with a multimeter

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There are quite a variety of active analog temperature sensor ICs that provide an output voltage proportional to the temperature. They usually don’t require any external calibration and signal conditioning, and as such their output can be directly fed to the input of an ADC for digital processing. A few examples of such sensors are LM34, LM35, TMP35/36/37, and MCP9701. If you are having any trouble using any of these sensors in your project, here is a quick way to test if your sensor is working or not.

Testing analog temperature sensor ICs with a multimeter

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A Digital temperature meter using an LM35 temperature sensor

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Introduction

A digital thermometer is a good choice of project for beginners who just stepped in to the world of microcontrollers because it provides an opportunity to learn using sensors to measure the real world signals that are analog in nature. This article describes a similar project based on a PIC16F688 microcontroller and an LM35 temperature sensor. LM35 is an analog sensor that converts the surrounding temperature to a proportional analog voltage. The output from the sensor is connected to one of the ADC channel inputs of the PIC16F688 microcontroller to derive the equivalent temperature value in digital format. The computed temperature is displayed in a 16×2 character LCD, in both °C and °F scales.

Theory

The LM35 series of temperature sensors are produced by National Semiconductor Corporation and are rated to operate over a -55 °C to 150°C temperature range. These sensors do not require any external calibration and the  output voltage is proportional to the temperature. The scale factor for temperature to voltage conversion is 10 mV per °C. The LM35 series sensors come in different packages. The one I used is in a hermatic TO-46 transistor package where the metal case is connected to the negative pin (Gnd).

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Real-time clock and Temperature display on 16×8 LED Matrix

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Digital clocks and temperature meters are very popular projects. There are tons of such projects available on internet. This one is little bit different. This displays time and temperature both scrolling on a 16×8 LED matrix.

PIC18F2550 is the brain of this project that controls the columns of the display through A6276 (a 16-bit serial input, constant current latched LED driver). The rows are controlled with a 74ACT164N (8-bit serial-in parallel-out shift register). The required current to drive the rows are provided by BC337 transistors.

A DS1320 serves as the external real time clock, whereas the temperature measurement is performed with LM35, a precision centigrade temperature sensor from National Semiconductors.

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Digital Thermometer Using PIC16F688 Microchip

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Digital Thermometers are very popular projects among students and hobbyists. If you have just stepped into the world of embedded system design, this project is worth to do. You will experience how the physical variables are measured in embedded world with sensors and are displayed in human readable format on LCD displays.

This project uses PIC16F688 Microchip as the main brain that reads the temperature measurements from DS1820, a digital temperature sensor from Maxim. DS1820 can measure temperatures ranging from -55 °C to +125 °C in 0.5°C increments. It is a digital sensor that provides temperature measurements in 9-bit digital format. The negative temperatures are provided in 2’s complement form. The author also provides the firmware, which is written in mikroC compiler. The temperature is displayed on a character LCD in Centigrade and Fahrenheit scales both.

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