Diagram SOlution

If you forget to switch off the light after leaving a seldom used room (such as the loft), there’s a strong likelihood that it could remain lit for months, running up an expensive power bill in the process. How can we prevent this waste?

It’s not hard for electronics enthusiasts to design a little circuit to mitigate the effects of absentmindedness. The notion is simple; if the light is left on when the hatch or door is closed, a rhythmic sounder/buzzer signal produces an alarm that hopefully will not be masked by other noise.

Circuit Diagram:

The circuit is powered as long as the lamp bulb is switched on by light switch S1. If the reed switch S2 then signals that the hatch has been closed, the sounder operates. The red LED, mounted outside the loft next to the entry hatch, also indicates that the lamp up there needs to be switched off. The circuit does not use a transformer, meaning that the whole circuit is at mains potential. For this reason the components must be placed inside an insulated plastic case for protection, with no way that people can touch any part of the circuit (this includes the sounder).

The connecting wires to the LED and the reed switch contact must be fully protected to the same touch-proof degree too. For the sounder you can use any type that operates on direct current in the region between 1 V and 3 V. In this circuit the operating voltage is limited by the LED connected in parallel to the buzzer. Using a red LED will provide around 1.7 V to the sounder. The current requirement of this kind of miniature sounder is about 5 mA.

Author: Stefan Hoffmann - Copyright: Elektor

The timer with Musical Alarm  use famous CMOS oscillator/divider IC (IC1 ). Although this circuit operates in 9V its standby current drain is very low. The time delay of timer circuit can be adjusted by adjusting the preset VR1. The base of npn transistor T1 is connected to pin 3 of IC1 through resistor R4 and its emitter terminal is connected with pin 2 of melody generator IC­ (IC2) in order to provide positive supply when adjusted time delay is over.

Timer with Musical Alarm Circuit Diagram

Here the zener diode ZD1 is used as regulator which reduce power supply to required for operation of IC2 i.e. 3.3V. Lastly for music output the output from pin 1 of IC2 is fed to loud speaker via driver transistor and its volume is controlled by preset VR2. For starting the timer power is supplied by pressing switch SW1. Link


Parts list

Resistor (all ¼-watt, ±5%)
R1 = 1.2 MΩ
R2 = 2.2 MΩ
R3 = 56 KΩ
R4, R5, R6 = 1 KΩ
VR1 = 1 MΩ
VR2 = 1 KΩ

Capacitors
C1 = 0.01 µF
C2 = 0.22 µF
C3 = 1 µF/25V

Semiconductors
IC1 = CD4060 (CMOS oscillator /divider IC)
IC2 = UM66 (melody generator)
T1, T2 = BC547

Miscellaneous
SW1 = on/off switch
9V battery
LS1 = 8Ω, 0.5W speaker

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Generally for connecting an LCD display to an Arduino using 7 strands, it usually breaks the leg that has any projects that remain few ports to be used. But there is a way, using an IC 74LS164 (8-bit serial shift register), a resistor and a diode, but its not just hardware, you have to use a library.

This Arduino library for connection of 2-wire or 3-wire using HD44780 compatible LCD display via shiftregisters. This circuit is considered "deprecated", but its worth testing.