Here is a simple circuit “AC Motor Speed Controller Circuit Using Microcontroller” which is used to control the speed of AC motor using microcontroller At89c51. The circuit uses the principle of changing firing angle of TRIAC in order to control the speed of motor. Here, in this project we had uses various switch in order to control the speed whereas LED bar graph is used to indicate the speed of motor.
Circuit Description: –
The circuit diagram of signal phase AC motor is divided into three main section.
- Firing angle control circuit
- Zero crossing detector circuit
- Speed indicating circuit
Firing angle control circuit:
The firing angle control section is shown in figure 1. This section consist of a microcontroller (At89c51) and opto-coupler (MUC3011). The opto-coupler is used to trigger TRIAC; whereas microcontroller is used to control the angle and indicating circuit. The output of zero crossing detector is given to external interrupt 0 (INT0) pin 12. Pin no.39 is connected to the input of opto-coupler whereas output is connected to gate of TRIAC.
The switches SW1, SW2, and SW3 is connected to pin 1, 2 and 3 respectively where diode D9, D8 and D7 are connected as shown in figure 1. Where the function of each switch is shown in Table 1.
|Switch 1 (SW1)||To switch on/off TRIAC|
|Switch 2 (SW2)||To Increase delay by 1 mS|
|Switch 3 (SW3)||To Decrease delay by 1 mS|
For power on reset capacitor C5 connected in series with resistor R9 as shown in circuit diagram.
Zero Crossing Detector Circuit: –
The zero-crossing detector circuit is shown in figure 2. It consists of voltage regulation section and zero crossing section. The input of 220V AC is given to primary winding of transformer T1 which is stepped down to 9V AC and changed to pulsating DC using bridge rectifier circuit. One output of rectifier is given to voltage regulator IC (IC1) through Diode D6. The output of regulator IC is pure 5V DC which is given to the collector of transistors T1 and T2 as biasing voltage.
Similarly, another output of rectifier through diode D5 is given to the base of transistor T1 through the voltage divider circuit comprise of resistors R2 and R3.
The output of transistor T1 is given to the base of transistor T2 where both the transistors acts as switch. The output of transistor T2 is given to pin 12 of IC2.
Indication Circuit: –
The indicating circuit is shown in figure 3. This circuit consist a bar-graph display and a current limiting resistor R7. This is used to indicate the condition of motor as well as speed of motor.
The LED connected to the pin no 16 of IC2 is to indicate zero crossing detector circuit status. This blinking LED represent zero crossing detector circuit is working ok.
The LED connected to pin 17 is used to indicate the motor power. When this LED is on it mean motor, power is enable if LED is off it means power is disable.
Software:- The source code for microcotroller is written in C and compiled where as for computer it is written in visual basic programming. The folder contains microcontroller code and visual basic code.
PARTS LIST OF AC MOTOR SPEED CONTROLLER CIRCUIT USING MICROCONTROLLER
|Resistors (all ¼-watt, ± 5% Carbon)|
|R1, R7, R10 = 220 Ω|
R2 – R6, R9 = 10 KΩ
R8, R11 = 1 KΩ
|C1 = 1000 µF/25V|
C2 = 1 µF
C3, C4 = 33 pF
C5 – C9 = 10 µF/16V
|IC1 = LM7805|
IC2 = AT89C51
IC3 = MAX32
IC4 = MOC3011
T1, T2 = 2N3904
TRIAC1 = BT138
D1 – D9 = 1N4007
LED1 = 5mm RED LED
BAR Graph Display = 10 LED combination
|XTAL1 = 12 MHz Crystal oscillator|
X1 = 220V AC to 0-9V AC 250 mA step down transformer
CON1 = Connector DB9
SW1-SW3 = Push to on Switch