This alarm activates when the illumination level changes from almost total darkness to a moderately high illumination level. When this happens the alarm is locked and the alarm signal, be it a light or a sound, remains active.
Fridge Door Alarm Circuit
Refrigerator door alarm circuit with two 555 timers
This refrigerator door alarm circuit alerts you when the door has been left open. Very important, because the power consumption increases when this happends. It uses the popular 555 timer IC
Dark detector circuit using LDR and relay
Dark detector circuit using LDR and relay
This circuit uses, as a main component, an LDR (photoresistor). An LDR changes its resistance value depending on the amount of light it received. The more light means less resistance, the less light means more resistance.
Light Operated Relay Circuit using LDR / Photoresistor
Light Operated Relay Circuit using LDR.
The LDR varies its value (ohms) depending on the amount of light that illuminates it. The more light less resistance and less light more resistance, A potentiometer is used to control the light level that activate the relay
Shadow detector alarm circuit with two LDRs
Shadow detector alarm circuit with two LDRs
This circuit detects if there is a difference of lighting between two LDRs, and sends an audible and visual warning. Circuits that use two LDRs are more reliable than those that use only one.
Automatic night light using 555 and relay
Automatic night light using 555 and relay
This Automatic night light using 555 IC turns lights on when there is no daylight. The circuit is perfect for lighting single places such as the garden, the front door of the house, the entrance to the garage, etc.