switch to Digital speed control of D.C motors

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INTRODUCTION
The Electrical and Electronics field of professionalism is going Digital. It is in this respect that the need to switch to Digital speed control of D.C motors that has led to the thought of this project.
In this era, speeds control of many D.C motors has been achieved through these methods:-
• Flux control method
• Voltage control method ;1)Multiple voltage control
2) Ward Leonard method
• Rheostat control method
In the above methods e.g. Ward Leonard method, large machines must be used in order to achieve speed control but this are very expensive and large capital outlay is required to buy the machines.
In this project, the use of digital inputs will be used to control the speeds of a dc motor. Therefore, to process the digital inputs a Digital to Analogue (F/V) converters will be used to sense and convert the speed into an appropriate voltage.



DESCRIPTION OF THE BLOCK DIAGRAM SUPPLY
This block will be used to supply source electrical energy to the circuit inform of ac.

RECTIFYING CIRCUIT
This will be used to convert ac to dc, the dc is varying.
555 TIMER
This will be used as a pulse generator
MC1483 (IC)
It’s an 8 pin digital to analogue converter the analogue output (VA) of digital to analogue converter is then compared to the analogue input signal (Vin) by a comparator.
SG3525
It’s a series of pulse width modulator integrated circuits are designed to offer improved performance and lowered external parts count when used in designing all types of switching power supplies.
MOTOR
It’s the output which is run in different directions by control of the switches.



2.1 RESEARCH METHODOLOGY
LITERATURE REVIEW
Operation of a DC Motor
Excited stator coils are assumed to produce south and north poles as depicted. Now if the armature is connected to a D.C source, current will be flowing through the armature conductors. Let the conductors under the influence of the South Pole carries⊗ currents and the conductors under the influence of North Pole carries currents. Applying Fleming's left hand rule, we note torque Te will be produced in the counter clockwise direction causing the rotor to move in the same direction. For steady speed operation, Te will be balanced by the mechanical load torque TL imposed on the shaft. Load torque TL will be in the opposite direction of rotation. It should be noted that when the armature conductors move in presence of a field, voltage is bound to be induced in the conductor (as explained in the previous section). The direction of this generated emf, ascertained by Fleming's right hand rule is found to be in the opposite direction of the current flow. In other words, the generated voltage in the armature acts in opposition to the source voltage. The generated voltage in a D.C motor is usually called the back emf, Eb.
There are various methods used to control the speed of a dc motor apart from digital speed control as stated by the following authors;-

According to Theraja (2003 page 972) it mentions rheostat speed control method which has the following limitations.

1) Speed changes with every change in loads because speed variations depend not only on the controlling resistance but also on load current. This double dependence makes it impossible to keep the speed constant or rapidly changing.
2) Large amount of power is wasted in the controller resistance. This loss of power is directly proportional to the reduction in speed which results to low efficiency.
3) This method also needs expensive arrangement for dissipation of heat produced in the controller resistance and hence gives speeds that are below the normal.

According to the book titled (Linear applications handbook page 430) it gives control of speed by use of tachometer. In which it drives the non-inverting input of the comparator up towards the preset reference level. As the motor slows down, the voltage from the change pump output falls and power is referred this speed as maintained by operating the motor in switching mode. Hysteresis can be provided to control the rate of switching.



ELECTRONICS COMPONENTS USED
These components are used in for the sound operation of the circuit.
1) LIGHT EMITTING DIODES (LEDS)
LEDS have been chosen due to the following:-
They are rugged small and have a long life.
They switch rapidly, no thermal lag caused by gradual cooling or heating in the frame.
They are also made in various ways hence much more flexible.
Input power required is low.
Good light intensity and brightness.