26-06-2012, 05:51 PM
Development of a Light Dependent Automatic- Off Timer for House Holds Electronics
[attachment=25673]
Abstract
This work was undertaken to design and construct a device that would be of use to persons who are in the habit of falling asleep while watching or listening to music. The scope of work ranges from the conceptualization of the idea and theories behind the operation of the device to the stage of packaging the design.
The unit provides automatic disconnection of the appliances from the alternating current (AC) mains supply upon the expiration of a pre-set time delay period. The system works by detecting a transition from light to darkness in a room, which triggers the device into a time-out mode. During the time delay period, the appliance e.g. CD (Compact Disk) player is connected to the mains supply. Disconnection occurs after the pre-set time delay period elapses.
Keywords
Automatic; Timer; Switching; Schmitt trigger; Relay; Oscillator.
Introduction
A switch can simply be defined as a device operated to turn electric current ON or OFF. Switches are important devices in electrical and electronics circuit design. They are
hence widely used components today serving as control devices in modern electrical systems and circuits. Switches can also be defined as devices by which a circuit parameter or signal such as electrical current can be either linked to or cut off from another part of a circuit manually or automatically [1].
The major aim of this paper is to effectively design and fabricate an electronic system that will be capable of switching off AC power supply automatically from electronic appliances connected to its output interface at night (in dark environments). This device therefore makes it possible for persons to use electronic appliances such as the television set and CD players as they await sleep leisurely late at night.
Pre-timer stage
The Schmitt trigger (the pre-timer unit) in Fig.2 is a logic state inverter which switches a high logic state at its input to a low logic state at its output and vice versa. The input voltage at the input of the 555 timer-based trigger is controlled by the voltage divider circuit consisting of the LDR (the light sensor) and the parallel combination of two resistors- 47kΩ and 100kΩ. The effective resistance of the parallel combination is given by:
Design Calculations
The major operational component in the timer stage is the 4060IC, which is a 14 stage binary ripple counter with built-in oscillator as shown in Fig. 3. The frequency with which the oscillator oscillates is determined by the value of the resistor, R and capacitor, C connected to pins 9 and 10 of the 4060IC respectively. Hence, the time delay period of the timer unit is pre-set by the value of these two components [2][6][7].
[attachment=25673]
Abstract
This work was undertaken to design and construct a device that would be of use to persons who are in the habit of falling asleep while watching or listening to music. The scope of work ranges from the conceptualization of the idea and theories behind the operation of the device to the stage of packaging the design.
The unit provides automatic disconnection of the appliances from the alternating current (AC) mains supply upon the expiration of a pre-set time delay period. The system works by detecting a transition from light to darkness in a room, which triggers the device into a time-out mode. During the time delay period, the appliance e.g. CD (Compact Disk) player is connected to the mains supply. Disconnection occurs after the pre-set time delay period elapses.
Keywords
Automatic; Timer; Switching; Schmitt trigger; Relay; Oscillator.
Introduction
A switch can simply be defined as a device operated to turn electric current ON or OFF. Switches are important devices in electrical and electronics circuit design. They are
hence widely used components today serving as control devices in modern electrical systems and circuits. Switches can also be defined as devices by which a circuit parameter or signal such as electrical current can be either linked to or cut off from another part of a circuit manually or automatically [1].
The major aim of this paper is to effectively design and fabricate an electronic system that will be capable of switching off AC power supply automatically from electronic appliances connected to its output interface at night (in dark environments). This device therefore makes it possible for persons to use electronic appliances such as the television set and CD players as they await sleep leisurely late at night.
Pre-timer stage
The Schmitt trigger (the pre-timer unit) in Fig.2 is a logic state inverter which switches a high logic state at its input to a low logic state at its output and vice versa. The input voltage at the input of the 555 timer-based trigger is controlled by the voltage divider circuit consisting of the LDR (the light sensor) and the parallel combination of two resistors- 47kΩ and 100kΩ. The effective resistance of the parallel combination is given by:
Design Calculations
The major operational component in the timer stage is the 4060IC, which is a 14 stage binary ripple counter with built-in oscillator as shown in Fig. 3. The frequency with which the oscillator oscillates is determined by the value of the resistor, R and capacitor, C connected to pins 9 and 10 of the 4060IC respectively. Hence, the time delay period of the timer unit is pre-set by the value of these two components [2][6][7].