Design of Hardware Module of Temperature Measurement and Control System Based on AT89C51 Single Chip Computer

This paper mainly introduces the most important part of the temperature measurement and control system based on AT89C51 single chip: hardware module design. The following are the various modules in the temperature measurement and control system and their working principle.

1 temperature detection module

The temperature measurement part of the system adopts the one-line digital temperature sensor DS18B20 produced by DALLAS. It has the advantages of miniaturization, low power consumption, high performance anti-interference ability, wide measuring range, strong easy to match processor, etc. DS18B20 can directly convert temperature. The serial digital signal is processed by the single-chip microcomputer. It has a three-pin TO-92 small-volume package. The temperature measurement range is -55 to +125 °C, and the temperature measurement resolution can reach 0.062 5 °C.

2 4×4 determinant button module

The system uses 4×4 determinant matrix button input. In addition to the 10 corresponding digital temperature buttons from 0 to 9, the temperature reset button, the OK button, the sub-zero temperature selection button and the decimal point button are also used to control the temperature. The system uses a non-encoded keyboard, and the key recognition uses a global scanning method.

3 main control module

The design uses AT89C51 microcontroller as the main control chip. The chip is a high-performance CMOS 8-bit microprocessor with 4 KB of flash memory, which is cost-effective and meets the system design requirements. In this system, the main control chip AT89C51 continuously compares the collected temperature signal with the input control temperature. If it exceeds the set range, the temperature rising or lowering device is started until the temperature reaches the set range.

4 temperature control module

In the temperature control circuit of the system, the single-chip microcomputer controls the relay through the on-off control of the triode to achieve the purpose of controlling the electric heater. When the temperature is lower than the lower limit of the set temperature, the MCU sends a low level signal to the high level after passing through the 74LS04 NOT gate circuit, so that the NPN type transistor is turned on, the relay makes the power supply and the electric heater connected, the electric heater is heated, and the temperature is slow. Slowly rise. When the temperature is higher than the upper limit of the set temperature, the MCU sends a high level signal to the low level after the 74LS04 non-gate circuit, so that the NPN type transistor is turned off, the relay makes the power supply and the refrigeration system connected, the refrigeration system works, and the temperature is slowly reduce. When the relay is suddenly powered off, a large reverse current is generated. The diode connected across the transistor can shunt the reverse current to protect the triode.

5 temperature measurement temperature display module

The design display part uses two 4-bit 8-segment common anode digital tubes 7SEG-MPX4-CA. One digital tube is used to display the current ambient temperature, and another digital tube is used to display the set temperature. In order to save the I/O port, this design connects the bit codes of two digital tubes through the 74LS04 dual 2-wire-4 line decoder.

The temperature measurement and control system designed in this paper uses DS18B20 digital temperature sensor to collect the ambient temperature in real time. The 4×4 matrix button is used to freely set the upper and lower temperature limits. The AT89C51 MCU is responsible for processing the collected temperature data and sending the control temperature signal, and setting the ambient temperature and temperature. The constant temperature is displayed in real time through the digital tube 7SEG-MPX4-CA.