Automatic outdoor light - shine a light on your door

The purpose of this circuit is to automatically switch on an outside light to illuminate your front door, when a visitor arrives. The circuit uses a light detecting resistor (LDR) as the sensor. For the circuit to work an external light source such as a lamp post is required. LDR J. Bodewes Needless to say this source needs to be close by. Please remember that the removal or repositioning of lamp posts needs the authority of the local coun- cil, so we do not recommend this circuit to anyone who has to extensively remodel the landscape. The LDR is mounted into a tube, behind a lens, and aimed at the light T1, T2, 73, T4, T5 = BC 547 source. This structure is positioned, so that the person approaching the front door, causes a shadow to fall onto the lens. Do not forget to ensure that the tube containing the LDR is water tight. Immediately the LDR is in shadow, its resistance will increase. This results in T1 applying a negative pulse to T2 via C1 and R6. T2 con- 1.0 82547 tinues to ...