Build Your Automatic Light-Off Circuit – 1V-3V

Description

Should a light fixture in an infrequently utilized space, for instance, an attic, remain illuminated after someone has departed, there exists a considerable possibility that a substantial electricity expenditure will occur over an extended period. How can this unnecessary waste be addressed? It's readily achievable for electrical hobbyists to construct a small circuit to counteract instances of forgetfulness. The concept is straightforward; when the door or hatch to the attic is closed, a periodic beeping signal generates an alert, hopefully one that won't be drowned out by other ambient sounds.

The circuit is energized as long as the lamp bulb is activated by switch S1. If the reed switch S2 then detects that the hatch is closed, the buzzer operates. A red LED, positioned externally beside the attic entry hatch, also indicates that the lamp within the attic necessitates being switched off. The design avoids the use of a transformer, thus maintaining the entire circuit at mains voltage. Consequently, all components must be housed within an insulated plastic enclosure to safeguard against accidental contact (including the buzzer).

Circuit diagram:

The connecting wires to the LED and the reed switch contact must be adequately shielded against accidental touch as well. For the buzzer, any type functioning on direct current within the range of 1 V and 3 V can be utilized. In this circuit, the operating voltage is restricted by the LED connected in parallel to the buzzer. Employing a red LED will supply approximately 1.7 V to the buzzer. The current demand of this kind of miniature buzzer is around 5 mA.