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PWM Motor

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Pulse Width Modulation Motor Speed Control

This image shows the Picaxe chip generating pulses of decreasing width.
This has the effect of slowing the conncted motor from 100% speed down to zero%.

Pulse Width Modulation

Here is a MOSFET motor driver.

Pulse Width Modulation

The Circuit Diagram

PWM Driver Circuit Diagram

And Finally the Code

    SYMBOL  COUNTER1 = B0
    SYMBOL  COUNTER2 = B1

INIT:
    COUNTER1 = 50    ; CONTROL THE PULSE HIGH TIME
    COUNTER2 =  0    ; CONTROL THE PULSE LOW TIME
    
START:
    DEC     COUNTER1 ; REDUCE THE HIGH PULSE WIDTH
    JPZ     INIT     ; NOTICE WHEN COUNTER1 HAS REACHED ZERO

    MOVW    0X01     ; SET OUTPUT HIGH
    MOVWR   PORTB    ; MOTOR IS CONNECTED TO PORTB
    MOVRW   COUNTER1 ; USED TO TIME THE HIGH PULSE
LOOP1:
    JPZ     NEXTBIT  ; IF ZERO, DO THE NEXT BIT
    SUBW    1        ; COUNT DOWN TOWARDS ZERO
    JMP     LOOP1    ; JUMP BACK TO CARRY ON COUNTING DOWN
    
NEXTBIT:
    INC     COUNTER2 ; INCREASE THE LOW PULSE WIDTH

    MOVW    0X00     ; SET MOTOR OUTPUT LOW
    MOVWR   PORTB    ; MOTOR IS CONNECTED TO PORTB
    MOVRW   COUNTER2 ; USED TO TIME THE LOW PULSE
LOOP2:
    JPZ     START    ; IF ZERO, JUMP TO THE START
    SUBW    1        ; COUNT DOWN TOWARDS ZERO
    JMP     LOOP2    ; JUMP BACK TO CARRY ON COUNTING DOWN