This project features a microcontroller-based dimmer circuit that controls the speed of a 220V-DC motor. The system includes a zero-crossing detector that generates a periodic pulse, helping to locate the starting point for triggering the Triac. The Triac is used to control the speed of the motor, resulting in precise and adjustable motor control.
1- The motor starting from stationary to avoid high starting current.
2- Motor acceleration and deceleration are controlled through the microcontroller, resulting in smooth speed transitions.
3- The system allows users to set a maximum speed for the motor, which is saved in non-volatile memory.
4- An LCD screen displays the motor speed and maximum speed in real-time, providing valuable feedback on the performance of the system.
The left part is triac driver with the load connected, this part is controlled by the microcontroller which is responsible of when to trigger the triac, after how many milliseconds of the starting point should I trigger the triac? the input of this part is connected to PA7.
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100nf capacitor is used to stablize the voltage on the variable resistor.
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LCD may has two additional pins: Anode and Kathode, which are connected to 5V and ground respectively.
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EEPROM AT24C02.
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EEPROM speed is 100Kbps which is suitable with 4.6k Ohm resistors.
- PE0 is "Enter" button which is used to set maximum speed.
- PE2,3 are "Up/Down" buttons which are used to customize maximum speed.
- Internal pull down resistors is set.
int main(void){
__asm(" CPSID I ");
PLLInit();
Sys_Init();
LCD_Init();
ADCInit();
BUTTONS_Init();
PortA_Init();
I2C_Init();
Update_max();
Timer2_Init();
LCD_Cmd(LCD_CLEAR);
Sys_Wait10ms(50);
__asm(" CPSIE I ");
The program is written using direct register access mode on TM4C123GH6PM microcontroller.
Initialization started with interrupts disabled, then PLLInit() is called to set system clock to 80MHz to be suitable for ADC module, after that systick timer is initialized by calling Sys_Init() which is used to create time delays only, then LCD operated on 4-bit mode by calling LCD_Init(), then ADC module on PE1 by calling ADCInit(), then the buttons used to change/customize the motor maximum speed on portE using BUTTONS_Init(), then portA which is responsible of capturing zero crossing signals and starting the timer2 by calling PortA_Init(), then I2C module which is used to communicate with EEPROM by calling I2C_Init(), then Update_max() is called which is used to recieve the maximum value stored in EEPROM to start the program with this value, then timer 2 which is used to triggering triac by calling Timer2_Init(), finally clearing LCD and enabling interrupts to start the program.
Triac is controlled using two types of interrupts : GPIO Interrupts on portA and Timer2 one-shot mode Interrupts.
GPIO interrupts is used to capture the signal of zero crossing detector, every time the AC voltage crosses 0V an interrupt happen.
// PortA ISR
// Changing motor speed depending on ADC value in accelerating/decelerating way
// ----------------------------------------------------------------------------
void GPIOPortA_Handler(void){
sample = convert(); // Sample from ADC
if(reload>sample){
reload -=280; // -3.5us (Acceleration)
}
else if(reload<sample){
reload +=280; // +3.5us (Deceleration)
}
Timer2A_Start(reload); // Start timer2
GPIO_PORTA_ICR_R |= (1<<6); // Clear flag
}
- PortA ISR job is starting timer2 with specific value depending on the value of variable resistor, starting from maximum reload value which is the most delay time before triggering triac to start motor from stationary and increase its speed gradually at specific rate.
The software comparing the sample coming from ADC with the value to reload the timer with (the same idea PI controller operates with).
// Timer2A ISR
// -----------
void Timer2A_Handler(void){
Trigger();
TIMER2_ICR_R = 0x00000001; // Acknowledge
}
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Timer2 ISR job is to trigger triac when its reload value goes from 1 to 0.
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The program display has just two screens, one to display motor speed and maximum speed and the other one to change the maximum speed, by calling the function update_screen() on the main program loop.
- User Input is handled by checking if user clicked buttons every time function BUTTONS_Check() is called by polling over the main program loop.
void BUTTONS_Check(void){
uint8_t max;
enter = GPIO_PORTE_DATA_R&(1<<0);
up = GPIO_PORTE_DATA_R&(1<<2);
down = GPIO_PORTE_DATA_R&(1<<3);
if(screen == 1){ // Main screen
if(enter && prev_enter == 0){
LCD_Cmd(LCD_CLEAR);
screen =2;
}
}
else if(screen == 2){ // Second screen
if(up){
inc_max();
}
else if(down){
dec_max();
}
else if(enter && prev_enter == 0){
// Send max value to be saved on startup
max = get_max();
I2C_Send(max);
// Clear screen on go to main screen
LCD_Cmd(LCD_CLEAR);
screen = 1;
}
}
prev_enter =enter;
}
- Enter button is used to switch between main and secondary screens, but it has another function, if used in the secondary screen, it saves the maximum value in the EEPROM.
Watch this 28-second video to see how changing the firing angle of the Triac affects the intensity of the light connected to the system.
The video shows the Tiva C Launchpad being used to control the intensity of the light. You can see how the light becomes brighter or dimmer as the firing angle is changed using the software interface.
LCD Software : Eng/ Mohamed Yousef Youtube ARM Playlist.