Posted on Friday, March 25, 2011 • Category: Test and Measurement
DS18S20 dual temperature meter uses two very exciting DS18S20 digital temperature sensors that come in convenient TO92 package. Unlike regular sensors where temperature readings are passed as varying voltage, DS18S20 passes temperature information in a digital format as data. This brings many new possibilities and enables to pass temperature information over much longer distances just over a two wire cable. With this capability temperature can be measured in different locations at the same time away from the main circuit board. With regular temperature sensors that rely on the voltage cables must be as short as possible because longer wire lengths introduce stray resistance and bring unreliable readings. Another great feature of DS18S20 sensor is that it doesn't require any calibration at all, while providing 100% accuracy out of the box. That means that you just plug it in and there's no need spending time recalibrating temperature readings. This is all due thanks to the nature of sending information in a digital format. In fact DS18S20 is just like a computer connected to the network that has a unique serial number identifier similar to an IP address. Multiple DS18S20 sensors can send information simultaneously, even over the same two wire bus cable. The two wires provide 3-5V voltage supply to the sensors and they are also used to pass data in two different directions. If wires are very long so that voltage on DS18S20 sensors drops below 3V external 5V voltage supply can be used with 1K resistor to power the sensors.
Once PIC microcontroller receives temperature information it converts it into both Celsius and Fahrenheit values so that they can be displayed on LCD display. DS18S20 dual temperature meter is capable of measuring temperatures from -55 to 125 °C degrees Celsius (-67 to 257 °F Fahrenheit) with 0.5 °C / 1 °F accuracy. If you just need to measure temperature in one location you may just use one DS18S20 sensor and PIC16F628 microcontroller will use just one sensor.
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