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PIC16C72 microcontroller based control system for air-conditioning circuit

Published on Oct 29 2010 // Micrcontroller circuits


PIC16C72 microcontroller based control system for air-conditioning circuit (1)2

 PIC16C72 microcontroller based control system for air-conditioning circuit (1)

Wall split air conditioning heat pump with its superior performance, are increasingly being selected by the majority of the family, its function is changing, and its function play a central role to improve the control system. This paper describes a PIC16C72 based control air-conditioning control system design.

The system has cooling, heating, dehumidification, automatic four kinds of modes, including the timing, sleep, wind, frost intelligence, emergency operation, commissioning, and five kinds of indoor wind speed adjustable control; at boot time can be According to the temperature between visits for intelligent judge, automatically adjust the time boot time, to avoid the boot is too cold or too hot; In addition, you can set the temperature and room temperature for two different temperatures temperature of 10 simultaneous instructions, and complete immunity and system protection.

The system is simple and reliable hardware, software has better control and interference. System has high performance and low cost.

1 controller principle

System CPU or a key input according to remote control commands, the temperature of collected intelligence judgments, and then make the appropriate cooling, heating or addition to temperature and running. And through the interface circuit, drive the compressor, valve, wind and indoor blower motor to make the appropriate action, and the temperature with LED indication. System block diagram shown in Figure 1.

2 Hardware Design
Block diagram of the system hardware design, it is necessary to consider the convenience of programming, but also take advantage of software features to simplify the hardware structure, that is to do “carrot and stick.”

SCM choice .1
3-way system temperature analog signal input, there is a way voltage and 1 current analog input, analog input requires a total of 5; and analog signals into digital signals to be converted to use the microcontroller CPU. To improve system performance and low cost, should be used with A / D converter MCU. After a comprehensive comparison of all aspects, we selected the U.S. company’s PIC16C72 Microchip microcontroller as the control. It has 5 analog input A / D converter analog input just to meet the system requirements. In addition, it is a chip integrates an 8-bit logical unit and working registers, 2KB of program memory, 128 data memory, three ports (A port, B port, C port) a total of 22 I / O lines , three timer / counters. In addition, only 35 easy to use and efficient RISC (reduced instruction set computer) instruction, while the chip with a watchdog function, and provides software to run error protection.
2.2 analog input circuit
The system for the direct use of thermistor temperature measurement, combined with a capacitor filter. Foreign exchange temperature detection circuit, because of interferences, Ortega on the diode limiter protection. Resistance values of the different sensors will be different partial pressure of the corresponding input of the PIC microcontroller’s A / D conversion port, the MCU internal conversion into digital signals. The detection circuit of simple structure, high cost performance. Because of 8-bit microcontroller used, so the temperature conversion accuracy, for 0.5 ?, fully air-conditioned to meet the signal detection accuracy.
Signal detection of overcurrent, without going through the comparator, saving resources; instead of using the analog signal directly after the partial pressure rectifier input comes through the microcontroller A / D converter, once every 500µs to its testing, and software compared to determine whether over-current.
On the detection of zero voltage signal is rectified by the partial pressure analog signal directly input. Two half-wave voltage for zero crossing detection must be so with the bridge rectifier. Analog input circuit shown in Figure 2.
2.3 The temperature indicating circuit
The circuit can set the temperature and room temperature of two temperature values the temperature of 10 simultaneous instructions, and simple structure, only with two I / O lines and the use of an eight shift register 74LS164. Method is to set the temperature to stabilize the instructions on the room temperature 1s interval flashing instructions. Remove the second temperature signal. If it is 21 ? or 30 ?, then the corresponding position directly into low, so that the corresponding LED lights, if the 22 ~ 29 ?, the temperature will be converted into the corresponding display code, CLOCK signal generated by RB6, RB7 serial send display code to 8-bit shift register 74LS164, then the LED indication.
2.4 The motor control circuit indoor wind
The control system automatically leaves of indoor wind, swing, and 5 fixed-angle operation. In order to obtain high-precision angle control, we used four-phase eight-shot DC12V Step Motor Drive. Stepper control circuit used in microcontroller RB2, RB3, RB4, RB5 as a four-phase (A, B, C, D) eight-shot ring distribution of timing, the current amplifier, power amplifier parts ULN2003 drive stepper motor. Control method is based on the current location of the target location and the angle difference, the output number of the corresponding number of pulse beat and shot by the different timing pulse output to control the reversing.
2.5 Indoor air control circuit
The size of the refrigeration and heating capacity and indoor fan speed has a close relationship. Indoor fan of the system shift control bidirectional thyristor to produce a voltage converter. Control circuit shown in Figure 3. In the internal microcontroller, according to RA5 port voltage zero crossing is detected as a sync signal, and through the timer control to generate the required phase and pulse width output from the RC1 mouth, and then amplified by the transistor, the pulse transformer isolated output, and then trigger the double transistor conduction. In order to reduce the pulse transformer capacity, the output is several successive narrow pulse sequences.