Automatic switching ON and OFF of lights in warehouses using micro processors and sen
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22-12-2010, 11:34 AM

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When we think about warehouses of today’s industries, the first thought that pops is “THE DARKNESS”. This paper deals with the automatic switching ON and OFF of lights in warehouses using micro processors and sensors. The circuit consists of two optical sensors, counters, phototransistors and relay switches. One optical sensor is installed at the entry door and another optical sensor is installed at the exit door of the ware house. The receiver sections of the sensors are connected to the photo transistors that produce voltage on incident light. When a person enters the warehouse, the rays from the optical sensor-1(at the entry door) are cut and hence the voltage produced by the photo transistor-1 is lowered. On this lowered voltage, the counter-1 increases its count by ONE. Similar connections are made with the sensor-2 (at the exit door). The rays from it are cut when a person leaves the warehouse.

The counter-2 that is connected to the sensor-2 will count the number of persons leaving the warehouse. A comparator is connected across both the counters. When the difference between the two counters is NOT ZERO, a signal is sent from the comparator to drive the relay switch in order to switch ON the lights. The switch is ON as long as the difference between the two counters is NOT ZERO i.e. as long as there is some person inside the warehouse. Thus the light is switched ON and OFF without manual switching ON. Moreover the energy can be saved because the lights are switched ON only when a person enters the warehouse and are switched OFF as soon as everyone leaves the warehouse. An external circuit for manual operation can be provided in case of emergencies.

Save energy by automatically switching the lights ON and OFF. The lights of the warehouse are switched ON when a person enters the warehouse and are switched OFF when there are no persons inside the warehouse. The above circuit consists of the following components:
 Opto isolator
 Photo transistors
 Microprocessors as counters
 Comparator
 Relay switches.
Let us discuss one by one:
Firstly the optical sensors can be classified as;
 The transmitting section,
 The receiving section.
TRANSMITTING SECTION: The transmitting section consists of an opto isolator. The transmitting section is an optical source that produces any form of optical light.
RECEIVING SECTION: The receiving section is an optical sensing device like a photo transistor. It consists of a photodiode.
COUNTERS: There are two counters used; one counter is to count the number of persons entering the warehouse and another counter to count the number of persons leaving the warehouse.
COMPARATOR: The output from the counters is fed to the comparator. The comparator compares the output of both the counters and the output signal from the comparator is fed to the relay switch.
RELAY: The relay switch is either switched OFF or switched ON depending upon the output of the comparator. The relay in turn switches ON or switches OFF the lights.

The optical transmitter transmits light and this light is sensed by the sensor which is nothing but a phototransistor. The phototransistor senses the light and produces voltage depending upon the intensity of the incident light. Whenever the light is cut(by a person entering the warehouse) a pulse is produced. The counter counts the pulses produced. There are two counters near the exit and entry doors. The outputs of the two counters are fed to a comparator. The comparator compares the two inputs and produces a corresponding output. Here when the difference is zero, there is no signal sent to the relay and hence lights remain OFF. The vice versa happens when the difference is NOT A ZERO. Hence the lights are switched ON.

Let us discuss about the components used in detail.
Opto-isolator (transmitter & receiver):
A common implementation is a LED and a phototransistor, positioned so that light from the LED will impinge on the photo detector. When an electrical signal is applied to the input of the opto -isolator, its LED lights and illuminates the photo detector, producing a corresponding electrical signal in the output circuit
With a photodiode as the detector, the output current is proportional to the intensity of incident light supplied by the emitter. The diode can be used in a photovoltaic mode or a photoconductive mode. In photovoltaic mode, the diode acts as a current source in parallel with a forward-biased diode. The output current and voltage are dependent on the load impedance and light intensity. In photoconductive mode, the diode is connected to a supply voltage, and the magnitude of the current conducted is directly proportional to the intensity of light. The optical path may be air or a dielectric waveguide.
The receiving section consists of a photo transistor as shown in the figure. The photo transistor in turn consists of a photodiode. It can be operated in any one of the mode either photoconductive or photo voltaic mode in the following manner. A photodiode is a PN junction or PIN structure. When a photon of sufficient energy strikes the diode, it excites an electron, thereby creating a free electron and a (positively charged electron) hole. If the absorption occurs in the junction's depletion region, or one diffusion length away from it, these carriers are swept from the junction by the built-in field of the depletion region. Thus holes move toward the anode, and electrons toward the cathode, and a photocurrent is produced.
Whenever the light is cut by a person entering the warehouse, a pulse is produced. This pulse is counted by the counters.

In digital logic and computing, a counter is a device which stores (and sometimes displays) the number of times a particular event or process has occurred, often in relationship to a clock signal. In practice, there are two types of counters:
 Up counters, which increase in value
 Down counters, which decrease in value


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