Thermistor Thermometer circuit

Posted on Feb 6, 2014

This is my student assignment for the class `Designing Microprocessor Based Instrumentation`. The board demonstrates the use of 12-bit ADC, writing c program with digital filtering and interface the LED display. The reading provides 0. 1C sensitivity. The optional input of the ADC is available for exercise with other input signals or sensors. The h

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ardware block diagram is shown in Fig. 2. The sensor is epoxy molded thermistor. The circuit for signal conditioning is simple voltage divider. The ADC is 12-bit SPI interface LTC1298 analog-to-digital converter. The microcontroller is ATMEL 89S52. The display has four digits 0. 5 inches 7-segment LED. The segment driver provides 32-bit CMOS output. The complete hardware schematic is shown in Fig 3. The ADC is 12-bit SPI interface LTC1298 or MC3202. There are two channels, CH0 and CH1. The input signal from thermistor for ADC channel 0 is simple voltage divider. Channel1 is available for other sensor. The sample shown in schematic is HIH-3160 Honeywell Relative Humidity Sensor. The ADC chip is interfaced with MCU, 89S52 with P1. 1, P1. 2 and P1. 3. The display has 4-digit LED. The 4094 CMOS shift register drives the LED directly.

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