Design of PIC microcontroller to send out natural wind to electric fan

1. Hardware circuit and principle

To make the electric fan send out natural wind, it is necessary to change the strength of the fan, that is, to change the voltage and current of the fan motor, thereby changing its speed. As shown in Figure 1, the fan socket is connected in series with the thyristor TREAC. By changing the thyristor control angle α, that is, controlling the time when the thyristor is turned on, the voltage and current of the fan motor can be changed. Figure 2 shows the relationship between the α angle and the motor load voltage.

The change of angle α can be achieved by changing the charge and discharge time of capacitor C1. The PIC16F84 microcontroller selects resistor Rx according to a certain rule to change the charge and discharge time of capacitor C1, thereby changing the conduction time of 2N2646. By changing the conduction angle of TREAC, the purpose of changing the strength of the fan is achieved. The relationship between the control angle α and the strength of the wind is shown in Figure 3.

If the mains frequency f = 50 Hz, then we can get the following formula: α/360° = t/0.02………………(1)

According to the RxC1 charging circuit shown in Figure 1, it can be inferred that

α＝t·360°/0.02＝{RxC1ln1［1/（1-n）］}·360°/0.02 …………（２）

Where η = VP / VBB, Vp is the voltage value of C1 after charging, VBB is the charging power supply voltage, and η = 0.63 is generally taken. If the capacitor C is 0.047μF, according to the value of (2), the Rx value table corresponding to different α setting values ​​is obtained:

R0=1kΩ, R1=33kΩ, R2=62kΩ, R3=89kΩ, R4=120kΩ, R5=150kΩ, R6=180kΩ, R7=220kΩ.

Rx is connected to RB0~RB7 ports of PIC16F84 microcontroller; RA0 port is the start signal input port. When the A key is pressed, the natural wind generator starts to work; RA1 port is the stop signal input port. When the B key is pressed, the natural wind generator stops running; RA3 port is the AC phase detection port. It is used to determine the starting phase of the AC.

Program Listing:

LSIT P=PIC16F84

#INCLUDEP16F84INC

FC EQU0CH

FD ＥＱＵ０ＤＨ

ORG ０

MAIN: CLRRW

TRISRB

MOVWFRB; set RB port as output port,

; and set its initial value to 0

MOVLW０ＦＨ

TRIS RA; Set port A as input port

KEYA: BTFSCRA, 0; Is the A key pressed?

ＧＯＴＯ ＫＥＹＡ ；A key is not pressed to go to

KEYA, wait

START: MOVLW80H; Press the A key,

; ８０Ｈ→Ｆ８

MOVWFF8

BTFSSRＡ，１；B key pressed No

ＧＯＴＯＭＡＩＮ ；B key pressed

PHASE: BTFSCRＡ３

GOTO PHASE ; Waiting for AC power

Zero Phase

MOVF8,W

MOVWFRB; F8 → RB port

CALL DELAAY; delay 10 seconds

ＣＬＲＣ ；清Ｃ

RRF F8; F8 right shift

BTFS3,0

GOTO PHASE

GOTO START

DELAY：MOVLW150

MOVWFF9

MOVLW7; Preset RTCC

Let the multiple be 1:256

OPTION

LOOP:MOVLW255

ＳＵＢＷＦＲＴＣＣ

ＢＴＦＳＳ ３２

DECFZF9

GOTO LOOP

RETLW ０

END; End of program