Embedded System for Automatic Washing Machine using Microchip PIC18F Series Microcontroller
The design uses the PIC18F series microcontroller. All the control functionalities of the system are built around this. Upgradeability is the unique feature of this system. Control card hardware and software allows the manufacturer to add or remove the features as per customer requirement and model. Thus once the whole system is designed it is very economic in large quantity production. Single-phase motor is considered for the design. Front panel consists of a keypad and LCD display. Keypad provides automatic and manual wash options to the user. LCD display is convenient to convey machine information to user. One more design possibility is to use brushless DC motors or three phase induction motor. These types of motors are very efficient but requires complex control algorithm. To implement such a complex and real time algorithm dedicated controller and software is required which a master controller controls. Even though cost is important criteria modern washing machines are designed with BLDC motors owing to efficiency and energy conservation. But in this assignment single phase universal motor has been used to design prototype due to its simplicity.
This include both hardware and software specifications.
- The system should provide fully automatic mode, semi-automatic mode and manual mode. Modes should be selectable by a keypad.
- Under fully automatic mode user intervention requirement should be zero. Once the system is started in this mode it should perform its work independently and after the completion of work it should notify the user about the completion of work. This mode instantaneously should sense cloth quality and requirement of water, water temperature, detergent, load, wash cycle time and perform operation accordingly.
- In semi-automatic mode also user requirement should be nil. But user has to choose any one of the semi-automatic mode in which washing conditions are predefined. Once the predefined mode is started the system should perform its job and after completion it should inform the user.
- In manual mode continuous intervention of user is required. User has to specify which operation he wants to do and has to provide related information to the control system. For example, if user wants to wash only, he has to choose ‘wash’ option in manual mode. Then the system should ask the user to enter the wash time, amount of water and the load. After these data are entered, the user should start the machine. When the specified operation is completed system should inform the user.
- When the lid is open system should not work. If door is accidentally opened in between wash operation, then the system should stop working in minimum possible time (<10s)>
- The system should provide all basic features of a washing machine like washing, rinsing, spinning, drying, cold wash, hot wash etc.
- The system should provide easy options for upgradeability of new features. The hardware and the software should be compatible to both machines, which have fewer features, or more features. Removal of any feature should not affect the working of any other features or overall working of the system.
- The system should work on single phase AC from 190VAC to 250VAC. The system should protect itself from power supply voltage variations.
- In the event of power failure, the washing machine should automatically start its cycle from the point of interruption when power is resumed.
Heart of this system is PIC18F452. Most of the peripheral features have been utilized to implement the design. Controlling the motor is very crucial part of the design. The PWM feature of the microcontroller controls motor speed. PWM output is fed to driver circuit and then to motor. To rotate the motor in two different directions ‘forward’ and ‘reverse’ direction control blocks are used. Motor speed sensor is interfaced to microcontroller. Microcontroller reads the speed of the motor and appropriately controls the speed of the motor in different phases of washing using PWM output. Door sensor, pressure sensor, keypad are also interfaced to microcontroller. Serial port in connected to GSM module. EEPROM and RTC are interfaced to MSSP module of controller. In circuit serial programming facility is provided for quick and easy programming and debugging.
A detailed schematic with pin connection of PIC microcontroller is provided in the Figure (1).
Figure (1) Block Schematic of Washing Machine Controller
Washing machine default parameters and user settable parameters are stored in external EEPROM. Internal EEPROM of the PIC is used to store status of the washing machine. The status is regularly logged to the internal EEPROM. In the event of power failure or whenever program resets, status flags are read from the internal EEPROM and thus status of the machine is determined and operation is continued from the point of interruption. Accessing of internal EEPROM is faster compared to external EEPROM. PIC18F452 provide 256 bytes of internal EEPROM that is not sufficient for storing parameters of machine. For this purpose external EEPROM is used. Depending on the mode flag and status flag conditions corresponding machine parameters are read from the external EEPROM and temporarily stored in RAM and operations are performed.
RTC DS1305 is interfaced to SPI port of the microcontroller. This RTC is used as timing reference for all timing calculation of machine. Whenever a particular mode starts RTC is initialized to zero and there onwards RTC is read and compared with the set timings; with the battery backup provision actual RTC can also be implemented. Since PIC allows either I2C or SPI mode at a time, whenever we need to access EEPROM or RTC, MSSP port of the PIC has to be configured to respective protocol.
In Circuit Serial Programming (ICSP) is accomplished using pins PGM, PGC, PGC and active low MCLR. These pins are also used to RB5, RB6 and RB7. To satisfy both conditions jumpers are provided. When programming of IC is required jumper settings ‘1’ has to be used. After programming, jumpers have to be replaced to setting ‘2’. This allows the use of RB5 to RB7 and brings the controller from programming mode to normal working mode. Thus ICSP helps speedy programming and debugging of software.
Some of the sensor outputs are fed to instrumentation amplifier to bring the output level to 0V to 5V range. Door (lid) sensor is connected to external interrupt 0. High priority is assigned to this interrupt. Thus opening of the door causes triggering of INT0 and INT0 ISR immediately stops the machine and informs the user. Analog input channels AN2, AN3 and AN4 can be used to upgrade the system with additional sensors.
Keypad is connected to PORTD. Keypad and meaning of keys are shown in Figure (2). Pull-up resistors are connected to RD0 to RD3 to enable keypad press detection. ORing RD4 to RD7 achieves this and output is given to external interrupt 1(INT1). When any of the keys is pressed ORed output becomes high and INT1 triggers. INT1 ISR does a keypad scan and appropriately performs the operation.
Motor speed sensor is given to T1CKI, which is an external clock input to timer1/timer3. Timer is configured in counter mode for calculating the speed. Speed is calculated by counting pulse output from the sensor for one second.
Figure (2) Keypad and Key Functions
Motor direction driver circuit determines the direction of the motor. Motor forward direction drives the current in forward direction and motor rotates forward. Motor reverse direction driver does the opposite of it. Software has to take care that both are not activated at a time. Speed of the motor is controlled using PWM driver. Speed of the motor and hence the drum varies in different phases of washing cycles. Speed profile of the washing machine drum is illustrated in Figure (3). Before changing the direction of the motor, PWM output must be made zero. PWM output is varied as per the calculated speed to maintain constant speed during wash cycles.
Figure (3) Speed Profile of Different Washing Cycles
Port pins RE1 and RE2 are fed to water valve drivers, which control the flow of water, while RE0 is connected to heater relay. Dedicated LCD with 3-wire interface is used. 3 wires consist of data line, clock and Chip Select (CS). Backlight control is also provided. GSM module is interfaced using serial port. Standard AT command set is used to communicate with GSM module.
It is assumed that when sensor outputs reach microcontroller inputs it has maximum swing of 0V to 5V. It is also assumed that PWM driver circuit controls gearbox and clutch mechanisms. Power supply circuits and regulators are not shown in the Figure (1). Suitably designed SMPS and AC regulators take care of power supply requirement of each block.
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