AT89C2051 Digital Thermometer and Clock

Posted on Feb 5, 2014

The MCU is ATMEL 89C4051 CMOS Microcontroller having 4kB code memory, 128 bytes On-chip RAM and 8-bit Port1 and Port3. The A/D chip is HARRIS CA3162, 3-digit DVM. The A/D converter employs dual-slope integrator providing 10Hz sampling rate. Digital output sent to MCU is multiplex four bit BCD started from MSD, LSD and NSD respectively.

AT89C2051 Digital Thermometer and Clock
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The MSD signal was tied to P3. 7 indicating first digit ready to be read. Integrating capacitor is a 330nF Polyester type. The 10k POT connected to pin13 is a gain adjustment and 50k POT to pin 8 and 9 is for zero adjustment. The input of the converter is true differential pin 11 for HI and pin 10 LO signal. Temperature was measured by a precision solid-state sensor from National Semiconductor, LM35D. The output signal is 10mV/ °C. Since the A/D converter is capable of providing 0-1000mV reading with 1mV resolution, thus the converter can resolve 0. 1 °C (not absolute accuracy). A 100k and 0. 02uF forms a first order low-pass filter used to be front-end hardware filtering. The 16x1 line LCD is connected in 4-bit interfacing to P1. 4-P1. 7 with control signal RS and E to P3. 4 and P3. 5 respectively. The +5V power supply uses a 78L05 TO92 case with external +9V adapter.

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