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28-02-2011, 09:25 AM
6 DIGIT LOCK CODE.doc (Size: 315 KB / Downloads: 68)
RESEARCH AND DESIGN METHODOLOGY
Basically, research on this project and implimentation was done both on the internet and on various Electrical/Electronic textbooks. Finally, we arrived at designing with polished wood and leather applied all round for proper finishing. The circuit was built around discrete electronics components including resistors, capacitors, transistors and as the microcontroller as the core.
BLOCK DIAGRAM DESCRIPTION
The key encoders provide all the necessary logic to fully encode an array of SPST switches. The keyboard scan is implemented internally by the microcontroller which constantly monitors the individual key that makes up the entire keyboard. These encoders also have on-chip pull-up devices which permit switches with up to 50k on resistance to be used. A Data Available output goes to a high level when a valid keyboard entry has been made. The Data Available output returns to a low level when the entered key is released, even if another key is depressed. The Data Available will return high to indicate acceptance of the new key after a normal debounce period; this two-key roll-over is provided between any two switches. An internal register remembers the last key pressed even after the key is released.
POWER SUPPLY UNIT
the power supply ection is built around a conventional components and also run directly from a 6VDC that is stabilised down to 5VDC for proper operation of the microcontroller. Below is the power supply circuit when running from the utility supply.
As seen on the above figure, in order to enable microcontroller to operate properly it is necessary to provide:
• Power supply
• Reset signal
• Clock signal
Obviously, all this is about very simple circuits, but it does not have to be always like that. If device is used for handling expensive machines or for maintaining vital functions, everything becomes more and more complicated! This kind of solution is quite enough for the time being. The circuit, shown on the figure above, uses cheap voltage stabilisator LM7805 and provides high-quality voltage level and quite enough current to enable microcontroller and “peripheral electronics” to operate (sufficient current in this case amounts to 1A)!
VISUAL DISPLAY UNIT: The visual display unit is used to show the current values of number of times attended work by the workers. It is built around the microcontroller which serves as the core for the system by outputting the desired values of information unto the display.
DC MOTOR UNIT: In general, DC motors are similar to DC generators in construction. They may, in fact, be described as generators “run backwards.” When current is passed through the armature of a DC motor, a torque is generated by magnetic reaction, and the armature revolves. The action of the commutator and the connections of the field coils of motors are precisely the same as those used for generators. The revolution of the armature induces a voltage in the armature windings. This induced voltage is opposite in direction to the outside voltage applied to the armature, and hence is called back voltage or counter electromotive force (emf). As the motor rotates more rapidly, the back voltage rises until it is almost equal to the applied voltage. The current is then small, and the speed of the motor will remain constant as long as the motor is not under load and is performing no mechanical work except that required to turn the armature. Under load the armature turns more slowly, reducing the back voltage and permitting a larger current to flow in the armature. The motor is thus able to receive more electric power from the source supplying it and to do more mechanical work.