1.0 Introduction
The automatic speed control of a Direct Current (DC) motor using Global System Mobile (GSM) modem is a device that controls the speed of a DC motor when data is transmitted from the GSM modem (phone). The speed control depends on the number keyed in from the phone. The GSM modem (phone) is connected to the hardware/circuit which receives the incoming data or information from the next other GSM modem (phone). The circuit decodes the incoming data from the other GSM modem (phone) and then varies/controls the speed of the DC motor accordingly.
The controlled DC motor is designed to run on DC electric power. The rotor consists of one coil of wire wound around a core on a shaft. An electrical power source is connected to the rotor coil through the commutator and its brushes, causing current to flow in to producing electromagnetism.
The commutator causes the current in the coil to be switched as the rotor turns, keeping the magnetic poles of the rotor from ever fully aligning with the magnetic poles of the stator field, so that the rotor never stops (like a compass needle does) but rather keeps rotating indefinitely (as long as power is applied and is sufficient for the motor to overcome the shaft torque load and internal losses due to friction, etc.)
The speed of the motor remains constant (as long as the motor is not under load or performing mechanical work except that required to turn the armature) until another key/number is keyed on the GSM modem(phone).when this is done, the motor receives electric power from the source supplying it and thus increases in speed.
The speed at which the DC motor operates depends on the strength of the magnetic field acting on the armature, as well as the armature current. The stronger the field, the slower is the rate of rotation needed to generate a back voltage large enough to counteract the applied voltage. For this reason, the speed of the DC motor is controlled by using the GSM modem (phone) to vary the field current.
The circuit consists of a microcontroller, DTMF decoder (Dialing Tone Modulation Frequency) and some biasing components.
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