Application example of single chip microcomputer in fully automatic washing machine

The fully automatic washing machine consists of a washing system and a control circuit. The control circuit is divided into mechanical and computer types. The computer type control circuit uses a single chip microcomputer as the core of the control circuit. Figure 1 shows the control circuit of a fully automatic washing machine composed of a single chip microcomputer Z86C09.
Ⅰ. Washing program of an automatic washing machine

There are 4 buttons K1, K2, K5 and K6 on the washing machine panel. K1 is used to select the water flow, which has two levels: normal water flow and soft water flow;

K2 is used to select the washing cycle, which can be washed, rinsed and dehydrated; K5 is the pause switch; K6 is the washing program selection key. The washing program is divided into standard program and economic program.

   The standard washing program of a washing machine is: wash - spin - spin - rinse - spin - rinse - spin. The economical washing program has one less rinse and spin process.

1. Cleansing process

After power is turned on, the washing machine enters the pause state so that the clothes can be put in. If no washing cycle is selected, the washing machine starts from the washing process.

When the pause switch K5 is pressed, the washing process begins. First, the water inlet valve FV is energized, the water inlet switch is turned on, and water is supplied to the washing machine; when the predetermined water level is reached, the water level switch K4 is turned on, the water inlet valve is de-energized and closed, and water supply stops; the motor MO is powered on, driving the impeller to rotate, forming a washing water flow. The motor MO is a forward and reverse motor, which can form a reciprocating water flow, which is conducive to washing clothes.

2. Dehydration process

After the washing or rinsing process is completed, the motor MO stops rotating, the drain valve MG is energized, and the water starts to drain.

The motor drives the inner tub to rotate. When the water level drops to a certain value, the water level switch K4 is disconnected, and after a period of time, the motor starts to rotate forward, driving the inner tub to rotate at high speed to spin dry the clothes.

3. Rinse process

The operation is the same as the washing process, but the time is shorter.

After all the laundry work is completed, a buzzer will sound, indicating that the clothes have been washed.

Ⅱ. Hardware composition principle of washing machine controller
  The washing machine controller is composed of single chip microcomputer Z86C09 as the core of the controller. The controller has the following characteristics:

(1) It has strong anti-interference ability. When it is subject to strong external interference and the program fails, it can automatically reset the system and re-execute the program.

(2) Use noise-free, electromagnetic interference-free bidirectional thyristors as control elements to control solenoid valves and motors.

(3) It has undervoltage and overvoltage protection. When undervoltage occurs, the controller does not work; when overvoltage occurs, the protection circuit works.

(4) It has a momentary power failure protection function. After a short power outage, when the voltage is restored, it can maintain the working status of the original running program and continue to complete the washing program.

(5) Various operations and the running status of the washing machine are displayed by LED.

The characteristics and composition principles of each part are introduced below.

1. Single chip microcomputer Z86C09

Z86C09 is the simplest type of Z8 series microcontroller, with low cost. It adopts COMS structure, with low power consumption and strong anti-interference ability.

It has strong and wide operating voltage, and can work in the voltage range of 2.5~5.5V. Z86C09 has 14 I/O lines, P2.0~P2.7 are bidirectional I/O ports, which can be set as input or output bit by bit. P3.1~3.3 of P3 port are specified as input ports, which can be used as input terminals or interrupt request terminals. P3.4~P3.6 are specified as output ports. Z86C09 contains 2 multi-function timers/counters, 2K bytes of ROM and 144 bytes of register array.

2. Power supply circuit

The power supply of the controller is composed of transformer B, rectifier diodes D14~D19, filter capacitor C1 and voltage regulator integrated circuit 7806.

The output voltage is divided into three paths, which are used for thyristor triggering, keyboard input and LED display, and power supply of single chip microcomputer. The last two paths pass through a diode and a capacitor respectively. When the output voltage of 7806 drops, the energy retained by the capacitor can be used to keep the circuit working for a while.

Transistors T11, T10 and voltage regulator DW form an undervoltage protection circuit. When the power supply voltage is insufficient, the base voltage of T11 is less than 3.9V.

When the power is off, T11 is turned off, and T10 is also turned off. There is no voltage at the P3.1 terminal of Z86C09, which is usually at a low level. T12 is turned off, causing the emitters of T5~T9 to be suspended, so T5~T9 are turned off and are not controlled by Z86C09. At this time, although Z86C09 can work normally, all peripheral control components are turned off and the washing machine does not work. The P3.1 terminal of the microcontroller inputs a signal to determine the working status of the undervoltage protection circuit. Only when the voltage is normal, the microcontroller starts to execute the washing program.

   When the power supply voltage exceeds the operating voltage, the resistance of the varistor MR will suddenly decrease, so that the voltage does not exceed the protection voltage value. When the overvoltage time is long, the fuse RD will burn out.

3. Zero-crossing detection circuit

The zero-crossing detection circuit is composed of transistor T14, transformer B and diodes D17~D19. D17 acts as an isolation. When the voltage is zero,

The pulsating voltage is zero and T14 is cut off. Since the collector resistor of T14 is connected to the collector of T10, only when T10 is turned on, that is, the power supply voltage is normal, can T14 output a high level when the power supply voltage passes zero. The P3.1 terminal of Z86C09 detects the zero-crossing signal.

4. Keyboard and display circuit

The keyboard consists of K1~K6, among which K3 and K4 are detection switches. The key status detection adopts the scanning method, which is controlled by P3.4~P3.6 of the single-chip microcomputer.

Output scanning signal, make transistors T1~T3 conduct in turn, the high level output by T1~T3 passes through diodes D1~D6 and scans each key. The 6 keys are divided into two groups, and the key signal is input by P3.2 and P3.3. P3.2 and P3.3 are normally low level. When a key is pressed and the high level scans this key, the input of P3.2 or P3.3 becomes high level. Z86C09 detects this high level, and then according to which bit is currently scanned, it can determine which key is pressed. The function of D1~D6 is to prevent short circuit of three scan lines when multiple keys are pressed at the same time.

    The display circuit is composed of LED1~LED7. The display mode adopts dynamic scanning mode. The column sweep signal line is shared with the row sweep line. The row display signal is directly driven by P2.4~P2.6 of Z86C09. Since the required brightness of LED is not high, the driving current is not large, about 9mA. The display time of each LED is 1/3 of the total display time, and the average current is about 3mA. [page]

5. Bidirectional thyristor trigger circuit

The bidirectional thyristor is triggered by DC. The gate of the thyristor is controlled by transistors T5~T8. When the transistor is turned on, the bidirectional thyristor is triggered.

Turn on, trigger the second to third quadrants, and the collector resistors of T5 to T8 are used to limit the current. Since the trigger current required by the 1A and 3A bidirectional thyristors is small, they are easily interfered by the outside world. In order to improve the anti-interference ability of the system, a 0.01uF capacitor is connected in parallel in the trigger circuit of the 1A and 3A bidirectional thyristors to suppress instantaneous interference signals. Two 8A bidirectional thyristors are used to control the forward and reverse rotation of the motor MO. At any time, only one of the two thyristors is allowed to be turned on. If both are turned on at the same time, the thyristor will be damaged. A 100Ω resistor and a 0.01uF capacitor are connected in parallel to the two main electrodes of the two 8A bidirectional thyristors to form a resistance-capacitance circuit, which is used to absorb the instantaneous voltage pulse between the two main electrodes of the bidirectional thyristor and protect the bidirectional thyristor.

    Note: The single-chip microcomputer in this article can also be constructed using AT89S51, etc.