Application of SPMC65P2408A in air conditioning

Introduction:
In recent years, the development of China's air conditioner industry is very rapid. In 2000, the production scale of China's air conditioner industry has developed to about 18 million units. In 2003, the total production capacity of China's household air conditioner industry exceeded 40 million units. In 2004, this figure has expanded to 55 million units. At present, China's air conditioner output accounts for about 3/5 of the world's total output. China has become a veritable air conditioner manufacturing power and is gradually becoming a global air conditioner production base. In the past five years, the total industrial output value and sales revenue of China's air conditioner industry have experienced sustained growth, among which the growth in 2001, 2003 and 2004 was particularly significant.
In addition, in recent years, the number of air conditioners owned by 100 urban households has increased significantly every year. The number of air conditioners owned varies greatly in different regions. With the expansion of the domestic market, China's air conditioner exports have also been growing rapidly year by year, and the share of air conditioner exports in the total export of household appliances has also been increasing. In 2002, 2003 and 2004, my country's air-conditioning exports maintained a very strong growth momentum. In 2003, the export volume of domestic air-conditioning enterprises exceeded 10 million units for the first time, exceeding 1,400 units. In 2004, the export volume of domestic air-conditioning enterprises exceeded 23 million units, which kept pace with domestic sales.

The main purpose of this article is to vigorously promote the application of SPMC65 series chips, verify their performance according to national standards, and introduce them to domestic home appliance manufacturers.
1 Working principle of air conditioner
(1) Refrigeration principle

Figure 1-1 Refrigeration principle of air conditioner

The air conditioning refrigeration principle is shown in Figure 1-1. When the air conditioner is working, the low-pressure, low-temperature refrigerant vapor in the refrigeration system is sucked into the compressor, compressed into high-pressure, high-temperature superheated vapor, and then discharged to the condenser; at the same time, the outdoor air sucked in by the outdoor fan flows through the condenser, taking away the heat released by the refrigerant, and condensing the high-pressure, high-temperature refrigerant vapor into a high-pressure liquid. The high-pressure liquid flows into the evaporator through the throttling capillary tube to reduce pressure and temperature, and evaporates at a corresponding low pressure, absorbing the surrounding heat; at the same time, the indoor fan allows the indoor air to continuously enter the fins of the evaporator for heat exchange, and sends the cooled gas after heat release to the room. In this way, the indoor and outdoor air circulate continuously to achieve the purpose of lowering the temperature.
(2) Heating principle

Figure 1-2 Principle of air conditioning heating
Air conditioning heat pump heating uses the compression condensation heat of the refrigeration system to heat the indoor air, as shown in Figure 1‑2. The low-pressure, low-temperature refrigerant liquid evaporates and absorbs heat in the evaporator, while the high-temperature and high-pressure refrigerant gas releases heat and condenses in the condenser. When the heat pump is heating, the circulation direction of the refrigerant is changed through the four-way valve, so that the indoor coil that originally served as the evaporator during cooling becomes the evaporator during heating. In this way, the refrigeration system absorbs heat outdoors and releases heat indoors to achieve the purpose of heating.

2 Function Introduction
◆ Refrigeration

1) Setting temperature range: 16℃～30℃, the default setting temperature is 24℃.
2) With anti-frost protection function.

◆ Dehumidification
In dehumidification operation mode, the set temperature is determined by the remote control, and the temperature setting range is: 16℃～30℃. The controller determines the operation mode according to the difference between the indoor temperature and the set temperature.

◆ Heating
1) Setting temperature range: 16℃～30℃.
2) With cold wind protection function.
3) With defrost function.
4) With high temperature protection function.

◆ Air supply mode
The wind speed can be switched between high, medium and low, and is not controlled by the set temperature.

◆ Scheduled on/off function
The scheduled on/off time is set in 10-minute units. When the scheduled time is reached, the air conditioner starts and stops working.

◆ Air flap working condition
1) The remote control can set the air flap to work in continuous mode or fixed mode.
2) Cooling, dehumidification, air supply and automatic swing air make a periodic swing of about 45° between 150° and 105°.
3) Heating swing air makes a periodic swing of about 60° between 90° and 150°.

◆ Healthy operation
It can generate healthy negative ions and sterilize the air in any mode.

◆ Automatic operation

When the remote control is set to automatic operation mode, the air conditioner automatically determines the operation mode based on the difference between the indoor temperature and the set temperature. The set temperature is 24℃ by default.

◆ Sleep

The scientific temperature-sleep curve automatically adjusts the indoor temperature to ensure that users have a very comfortable sleep.

◆ Emergency switch

If the remote control is lost or damaged, you can use the emergency switch to turn on, shut down, cool or heat the device.

3 System Overall Solution Introduction
The hardware block diagram is shown in Figure 3‑1. It is mainly composed of CPU, signal detection and control parts. The CPU first receives the infrared signal sent by the remote control, obtains the command parameters, and detects environmental variables (temperature, overcurrent, power failure, etc.), then conducts comprehensive analysis and issues commands to control the normal operation of various components of the air conditioner. The display panel can display the current working status of the air conditioner.

Figure 3-1 Hardware block diagram

4 System Hardware Design
4.1 Air Conditioning Circuit Principle
The hardware circuit is shown in Figure 4‑1. According to the different working voltages, the whole system can be divided into three parts: micro-control system, relay control and strong power control, which work at DC5V, DC12V and AC220V respectively.

Figure 4-1 System circuit schematic diagram
4.2 Introduction to chip features
SPMC65P2408A is an 8-bit industrial-grade microcontroller designed and developed by Lingyang Company. It uses Lingyang SPMC65 core and supports bit operation instructions. It has powerful timer/counter, rich external interrupt sources, ADC, PWM, standard communication interface and other functions. It is suitable for general industrial control occasions, computer peripheral control and home appliances. SPMC65P2408A has two packages: 28-pin and 32-pin. The 32-pin package has an additional UART function. This design uses a 28-pin package, as shown in Figure 4-2.

The specific characteristics of the 28-pin packaged chip are as follows:
l Operating voltage: 3.0V ~ 5.5V
l Operating speed: 8MHz
l Operating temperature: -40℃ ~ 85℃

l Super strong anti-interference and anti-static ESD protection capabilities

l 8K byte ROM, 256 byte RAM

l 23 general purpose input and output ports

l Powerful timing counters: 2 8-bit, 2 16-bit with CaptureComparePWM function

l 1 1Hz～62.5KHz time base

l 8-channel 10-bit precision ADC (with external reference voltage)

l 4 external interrupts, 11 internal interrupts

l SPI serial communication interface

l 2 power saving modes: Halt, Stop

l Buzzer output function

l 4.0V/2.5V optional low voltage reset function

l Programmable watchdog function

Figure 4-2 SPMC65P2408A*28P package

4.3 Power supply system analysis
There are three voltages on the entire main control board: AC220V, DC12V and DC5V. AC220V directly powers the compressor, outdoor fan, indoor fan and negative ion generator; AC220V is stepped down to DC12V and DC5V, which are used to power the relay and microcontroller system. The power supply system is shown in Figure 4-3. AC220V is first stepped down by a transformer, then input from socket J1, and then full-wave rectified by a rectifier bridge, filtered by capacitor C2, and DC12V is obtained. Then, it is stabilized by the voltage regulator 7805 to obtain DC5V. The sampling point ZDS in the figure is used for zero-crossing detection, and the diode D1 prevents the filter capacitor C2 from affecting the sampling point ZDS.

Figure 4-3 Power supply system

4.4 Zero-crossing detection circuit
The zero-crossing detection circuit is shown in Figure 4-4. It is used to detect the zero-crossing point of AC220V. The full-wave rectified signal is sampled in the rectifier bridge circuit, and the signal is shaped into a pulse wave through a transistor, resistor and capacitor to form a shaping circuit. It can trigger an external interrupt and perform zero-crossing detection. The sampling point and the shaped signal are shown in Figure 4-5.

The purpose of zero-crossing detection is to control the trigger angle of the optocoupler thyristor, thereby controlling the wind speed of the indoor fan.

Figure 4-4 Zero-crossing detection circuit

Figure 4_5 Sampling points and shaped signal

4.5 Control of indoor fan
Figure 4-6 shows the indoor fan control circuit. U1 is an optocoupler thyristor, which is used to control the conduction time of AC220V, thereby adjusting the wind speed of the indoor fan. Pin 3 of U3 is the trigger pin, which is driven by a transistor. AC220V is input from pin 11 and output from pin 13. The specific conduction time is controlled by the trigger angle.

Specific control method for indoor fan speed: First, the zero-crossing detection circuit detects the zero-crossing point of AC220V and generates a zero-crossing interrupt; then, in the interrupt processing subroutine, turn on the timing function of the Timer, such as timing 4ms, and after 4ms, the CPU generates a trigger pulse, which is driven by the transistor and input from the 3rd pin of U3, triggering the internal circuit of U3, thereby turning on the pins 11 and 13 of U3, and AC220V supplies power to the indoor fan. In this way, the conduction time of AC220V in each half cycle can be controlled by changing the timing length of the timer, thereby controlling the power and speed of the indoor fan.

Figure 4-6 Indoor fan control circuit

4.6 Indoor fan speed detection
When the indoor fan is working, the speed sensor feeds back the speed of the indoor fan in the form of a sine wave. The frequency of the sine wave has a specific corresponding relationship with the fan speed, as shown in the table below. The sine wave is shaped into a square wave by a transistor, and the CPU uses an external interrupt to detect the frequency, thereby realizing the measurement of the wind speed.

Wind speed	high	middle	Low
Fan frequency (Hz)	70	50	30

Figure 4-7 Indoor fan wind speed detection circuit

4.7 Overcurrent detection circuit
The current transformer L1 is used to detect the change of the current on the live wire. In the figure, L1 is a current transformer, which outputs 0-5mA AC. When the current suddenly increases, the output current of the current transformer also increases. After full-bridge rectification, current-voltage conversion, and low-pass filtering, a DC voltage signal is output from the COD end. The CPU senses the change of AC220V current by AD acquisition of the voltage at the COD end. When the voltage at the COD end is too high, the CPU can take protective measures for the circuit.

Figure 4-8 Overcurrent detection circuit

4.8 Low voltage detection circuit
Using the principle of resistor voltage division, the CPU uses AD acquisition to detect the 12V voltage at the front end of 7805. When the power grid is powered off, the AD end will collect the reduction of the 12V voltage at the front end of 7805. Due to the existence of the capacitor at the output end of 7805, even if the 12V voltage drops to 6V, 7805 can still provide 5V voltage to enable the CPU to work normally. At this time, the CPU immediately saves the current operating parameters of the air conditioner in AT24C01.

Figure 4-9 Low voltage detection circuit

4.9 Control of compressor, four-way valve, outdoor fan and negative ion generator (healthy operation)
The compressor, outdoor fan, four-way valve and negative ion generator are all powered by AC220V, so the operation of each part can be controlled by controlling the on and off of AC220V through the relay.

R1 is a varistor for overvoltage protection. SI1 is a fuse.

Socket J2 is the AC220V output terminal. An external transformer is used to step down the AC220V. After the step-down, it is connected to the power module to obtain DC12V and DC5V respectively.

Figure 4-10 Compressor, four-way valve and control circuit for healthy operation

4.10 Driving Circuit
The relay, buzzer and stepper motor are all controlled by 12V DC voltage, and U4 is the driving chip.

Neg-lonC controls the relay of the negative ion generator;

ValveC controls the relay of the four-way valve;

ComprC controls the compressor relay;

Buzzer controls the buzzer;

A, B, C, and D are the four phases of the stepper motor.

Figure 4-11 Driving circuit

4.11 Power-off memory
U5 (AT24C01) is used as a serial memory chip to save the operating parameters of the air conditioner before the power outage. The chip only needs two lines to control: clock line SCL and data line SDA/Ion, and the memory size is 128×8 bytes.

Figure 4-12 Power-off memory circuit
5 System software design
5.1 Main
process The main program flow is shown in Figure 5-1. The main cycle time is 10ms and the time base is used for timing.

First, wait for 10ms to arrive. When 10ms arrives, decode the remote control signal, select the working mode of the air conditioner according to the decoded information, and then enter the mode to execute.

Figure 5-1 Main flow chart

6 Conclusion
The SPMC65 series chips are suitable for various public control occasions with excellent performance and rich resources. The air conditioner main control board developed with SPMC65P2408A as the main control chip has passed the EFT test without special EMC prevention and control, and its anti-interference ability has reached the national highest level of ±4KV.