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كل ما تحتاجه للسيطرة على محرك Dc ( اتجاه وسرعة ) والدائرة مجربة وذو كفائة جيدة

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    كل ما تحتاجه للسيطرة على محرك Dc ( اتجاه وسرعة ) والدائرة مجربة وذو كفائة جيدة

    DC Motor Speed and Direction Control
    One application of the 8254 timer is as a motor speed controller for a DC motor. Figure 11—45 shows the schematic diagram of the motor and its associated driver circuitry. It also illustrates the interconnection of the 8254, a flip-flop, and the motor and its driver.
    The operation of the motor driver circuitry is straightforward. If the Q output of the 74ALS 112 is a logic 1, the base Q2 is pulled up to +12 V through the base pull-up resistor, and the base of Q2 is open circuited. This means that Qi is off and Q2 is on, with ground applied to the positive lead of the motor. The bases of both Q3 and Q4 are pulled low to ground through the inverters. This causes Q3 to conduction or turn on and Q4 to turn off, applying ground to the negative lead of the motor. The logic 1 at the Q output of the flip-flop therefore connects + 12 V to the positive lead of the motor and ground to the negative lead. This connection causes the motor to spin in its forward direction. If the state of the Q output of the flip-flop becomes a logic 0, then the conditions of the transistors are reversed and + 12 V is attached to the negative lead of the motor, with ground attached to the positive lead. This causes the motor to spin in the reverse direction.
    If the output of the flip-flop is alternated between logic 1 and 0, the motor spins in either direction at various speeds. If the duty cycle of the Q output is 50 percent, the motor will not spin at all and exhibits some holding torque because current flows through it. Figure 11-46 shows some timing diagrams and their effects on the speed and direction of the motor. Notice how each counter generates pulses at different positions to vary the duty cycle at the Q output of the flip- flop. This output is also called pulse width modulation.

    http://www.arab-eng.org/vb/attachmen...1&d=1148534170




    To generate these wave forms, counters 0 and 1 are both programmed to divide the input clock (PCLK) by 30,720. We change the duty cycle of Q by changing the point at which counter 1 is started in relationship to counter 0. This changes the direction and speed of the motor. But

    why divide the 8 MHz clock by 30.720? The divide rate of 30,720 is divisible by 256, so we can develop a short program that allows 256 different speeds. This also produces a basic operating frequency for the motor of about 260 Hz, which is low enough in frequency to power the motor. It is important to keep this operating frequency below 1000 Hz, but above 60 Hz.
    Example 11—27 lists a procedure that controls the speed and direction of the motor. The speed is controlled by the value of AH when this procedure is called. Because we have an 8-bit number to represent speed. a 50 percent duty cycle, for a stopped motor. is a count of 128. By changing the value in AH when the procedure is called, we can adjust the motor speed. The speed of the motor will increase in either direction by changing the number in AH when this procedure is called. As the value in AH approaches OOH, the motor begins to increase its speed in the reverse direction. As the value of AH approaches FFH, the motor increases its speed in the forward direction.


    The procedure adjusts the wave form at Q by first calculating the count that counter 0 is to start in relationship to counter 1. This is accomplished by multiplying AH by 120 and then subtracting it from 30,720. This is required because the counters are down-counters that count from the programmed count to 0 before restarting. Next, counter I is programmed with a count of 30.720 and started to generate the clear wave form for the flip-flop. After counter 1 is started, it is read and compared with the calculated count. Once it reaches this count, counter 0 is started with a count of 30.720. From this point forward, both counters continue generating the clear and set wave forms until the procedure is again called to adjust the speed and direction of the motor.





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    اذا كان لدينا محرك يعمل بتيار مستمر 24 v هل نستخدم نفس الدائرة او ماذا ؟
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