Design of PIC16F84 single chip microcomputer to control 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:

100% working days.

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

＃ＩＮＣＬＵＤＥ Ｐ１６Ｆ８４ＩＮＣ

ＦＣ ＥＱＵ０ＣＨ

ＦＤ ＥＱＵ０ＤＨ

ＯＲＧ ０

ＭＡＩＮ：ＣＬＲＷ

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 exit

CALL DELAAY; delay 10 seconds

ＣＬＲＣ ；清Ｃ

RRF F8; F8 right shift

ＢＴＦＳＳ３，０

ＧＯＴＯ ＰＨＡＳＥ

ＧＯＴＯ ＳＴＡＲＴ

ＤＥＬＡＹ：ＭＯＶＬＷ１５０

ＭＯＶＷＦＦ９

MOVLW7; Preset RTCC

Let the multiple be 1:256

ＯＰＴＩＯＮ

ＬＯＯＰ：ＭＯＶＬＷ２５５

ＳＵＢＷＦＲＴＣＣ

ＢＴＦＳＳ ３２

ＤＥＣＦＳＺＦ９

ＧＯＴＯ ＬＯＯＰ

ＲＥＴＬＷ ０

END; End of program