This mini DigiThermo is a device specially designed for measuring and time and temperature in chemistry laboratory.
The following picture demonstrates the circuit diagram of DigiThermo.
- The MCU: ATMEL 89C4051 CMOS Microcontroller with 4kB code memory, 128 bytes On-chip RAM and 8-bit Port1 and Port3.
- The A/D chip: HARRIS CA3162, 3-digit DVM.
- The A/D converter employs dual-slope integrator providing 10Hz sampling rate, while Digital output sent to MCU will be multiplexing four bit BCD started from MSD, LSD and NSD respectively.
- Integrating capacitor: 330nF Polyester.
- The 10k POT that connected to Pin 13 is a gain adjustment, while 50k POT to pin 8 and 9 is for zero adjustment purpose.
- Pin 11 for HI and Pin 10 for LO for differential the input of converter.
- LM35D used for temperature measurement tool.
- The output signal is 10mV/°C.
- First order low-pass filter acts as front-end hardware filtering is forming by a 100k and 0.02uF.
- The 16×1 line LCD is connects in 4-bit interfacing to P1.4-P1.7.
The +5V power supply uses a 78L05 TO92 case with an external +9V adapter.