CONSTRUCTION OF AN AUTOMATIC NIGHT LAMP


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CONSTRUCTION OF AN AUTOMATIC NIGHT LAMP

AIM



To construct a night lamp which switches on automatically when darkness comes in the evening.

MATERIALS REQUIRED



  • Resistance [2] i150K,1W] and [47K, 1/2W]
  • Rheostat [1K Preset]
  • Triac [400V, 1A]
  • Diac
  • LDR
  • Lamp [100W]
  • PCB


  • INTRODUCTION



    It is very convenient to light a lamp in our absence in the evening when it gets dark. This circuit can be used to light the staircase light, porch light etc. using domestic ac supply. It is very inexpensive construction and we don’t have to employ or depend anybody to put on the light when we are out of station.

    THEORY



    An LDR and a triac together plays the role of automation of this circuit. Triod AC Switch [Triac] is a power switching device as in the circuit as in the SCR. The triac conducts current in both directions while the SCR allows current only in one direction. It has anode, cathode and gate at its terminals. It behaves as an open switch as long as the cathode – anode voltage is less than the breakover voltage of the device. It behaves like a closed switch as the cathode – anode voltage exceeds the breakover voltage by giving a trigger pulse at the gate terminal. After that’ it continues to behave like a closed switch even after the removal of trigger pulse. It goes back to the open state, only when anode – cathode voltage goes to zero or become negative. The resistance of LDR is low during daytime and high during night time. Ie, the required trigger pulse is developed across it when it becomes dark and it is applied across the gate cathode terminals and triac is triggered.


    EXPERIMENTAL PROCEDURE





    Connections are made as shown in the diagram. The circuit mes active only when the LDR is exposed to darkness. When the circuit is closed by closing switch, S. AC voltage rises from zero to a peak value of about 330 volts [230xsq. Root of 2] during all positive half cycles cathode – anode of the triac. The same voltage after division by the potential divider formed by resistance and LDR appears at the gate. Since the triac has a breakover voltage less than the peak value of the AC input, the triac will remain open as long as the gate voltage is inadequate to trigger it to the ON state. This is what exactly happens during the daytime when the LDR resistance is extremely low. As it becomes dark, the LDR resistance increases and at a certain darkness level, the voltage across it that appears at the gate is sufficient to trigger the triac. Now, the triac get closed and the bulb lights up. The bulb again comes to the OFF state only if the LDR is exposed to day light or switch, S is switched off.

    CONCLUSION



  • The sensitivity of LDR to light is studied
  • The property of triac to get triggered and becomes conducting as and when desired is understood.


  • PRECAUTIONS



  • Do not touch the exposed parts of the circuit since the circuit is handling the domestic AC supply.
  • It is better to keep the circuit switched off when it is not in use.


  • REFERENCE



  • Thomas E V., A Manual of Practical physics, Tess Publisher, Thiruvalla.
  • Maini A K., Electronic Projects for Beginners, Pustak Mahal, NewDelhi.
  • Albert Paul Malvino, Electronic Principles, Tata Mcgraw Hills


  • Project Feedbacks

    Author: Member Level: BronzeRevenue Score: 2 out of 52 out of 5
    Even though i had connected as per the circuit diagram, the bulb is glowing continuously even the LDR is exposed to darkness.
    Can anyone please help me regarding my porblem??????


    Author: Member Level: BronzeRevenue Score: 2 out of 52 out of 5
    Even though i had connected as per the circuit diagram, the bulb is glowing continuously even the LDR is exposed to darkness.
    Can anyone please help me regarding my porblem??????


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