Many a times equipment at workstations remains switched on unnoticed. In this situation, these may get damaged due to overheating. Here is an add-on device for the workbench power supply that reminds you of the power-on status of the connected devices every hour or so by sounding a buzzer for around 20 seconds. It also has a white LED that provides good enough light to locate objects when a main fails.
Here, IC NE555 is wired as an as table multi-vibrator, whose time period is set to around six minutes using resistors, preset for sounding the buzzer every hour. The output of IC 555 is fed to the clock input of IC CD4017.. When power to the circuit is switched on, pin 3 of IC CD4017 goes high. After around one hour, its output pin 11 goes high and the buzzer sounds. This cycle repeats until the two NPN transistors. The LDR offers a very high resistance in darkness.