Quartz crystal-based remote thermometer features direct Celsius readout
Jim Williams and Mark Thoren, Linear Technology Corp; Edited by Brad Thompson -- EDN, March 17, 2005
Although quartz crystals have served as temperature sensors, designers haven't taken advantage of the technology because few manufacturers offer the sensors as standard products (references 1 and 2). In contrast to conventional resistance- or semiconductor-based sensors, a quartz-based sensor provides inherently digital-signal conditioning, good stability, and a direct digital output that's immune to noise and thus ideally suited to remote-sensor placement (Figure 1).
An economical and commercially available quartz temperature sensor, Y1 and IC1, an LTC-485 RS485 transceiver in transmitter mode, form a Pierce crystal oscillator. The sensor, an Epson HTS-206, presents a nominal frequency of 40 kHz at 25°C and a temperature coefficient of –29.6/ppm/°C (Reference 3). The transceiver's differential-line-driver outputs deliver a frequency-coded temperature signal over a twisted-pair cable at distances as far as 1000 ft.
A second LTC-485, IC2, in receiving mode, accepts the differential data and presents a single-ended output to IC3, a PIC-16F73 processor that converts the frequency-coded temperature data and presents the temperature in Celsius format on LCD1. Click here to download the conversion program's source code.
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the incorrect listing has been fixed--thanks to those who pointed it out to us.
Bill Schweber - 2005-18-3 06:54:00 PST -
The listing file posted is incorrect, not for this Design Idea.
Lew Whitacre - 2005-18-3 04:59:00 PST -
Quartz crystal-based remote thermometer features direct Celsius readout, Jim Williams and Mark Thoren, Linear Technology Corp; Edited by Brad Thompson -- EDN, 3/17/2005
The link to the source code for the above design idea is not correct. What is the correct link?
David Desrosiers - 2005-18-3 02:53:00 PST
