Digital DC Motor Speed Control With LED Display


Posted on Feb 5, 2014

Various techniques can be used to control the speed of a dc motor, such as using the phase-locked-loop principles, digital inputs, or analog inputs. If desired, the speed of the motor may also be monitored with LED or LCD displays. The project digital DC motor speed controller illustrates the use of digital inputs to control the speed of a dc motor.


Digital DC Motor Speed Control With LED Display
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To process the digital inputs, a D/A converter will be used, while a combination of a speed sensor and F/V converter will be used to sense and convert the speed into an appropriate voltage. Figure 1-1 shows the block diagram of a digitally controlled dc motor. The output of the D/ A converter is proportional to the binary equivalent of its digital inputs. The differential amplifier compares the D/A converter output with the output voltage of the F/V converter. The resulting difference voltage is an input to the power amplifier/driver stage. The output of the power amplifier/driver then drives the dc motor. The speed sensor converts the motor`s speed into a pulse waveform, which is in turn converted into a proportional voltage by the F/V converter since the output of the F/V converter is processed using a negative feedback formed with the differential amplifier, the motor is kept at a constant speed corresponding to the setting of the digital inputs. In fact, the key to the operation of the circuit is that the differential amplifier maintains a specific difference between two input voltages so that motor speed is constant at the selected digital input setting. Since the output of the D/A converter is directly proportional to the binary equivalent of its digital inputs, the output voltage of the D/A converter will be maximum positive when all the inputs are logic 1. This means that when all inputs are logic 1 the motor will...




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