Light Alarm With IC 555
Alarm circuit is a combination light switch circuit in the control electronics with light and built an astable multivibrator circuit with IC 555. This light disupplay alarm circuit with a 9 volt battery so that the circuit light alarm can be applied to cabinets or safes. Light switch circuit used in the circuit light alarm is an LDR and transistor. Light sensitivity of the alarm circuit can be adjusted by setting VR100K until light acceptance condition to activate the alarm as you wish. A complete range of light alarm can be seen in the following figure.
Light alarm circuit with IC 555
The working principle of light alarm is initiated when the alarm circuit is turned on. The light sensor will be detecting light received, if the received light enough then BC158 PNP transistor will have the bias and the transistor ON position so that the multivibrator circuit gets triggered resulting in oscillations in the circuit of the multivibrator and the pulse generated from the oscillation is transmitted to the speakers so the alarm goes off . Astable multivibrator circuit above works on a 1kHz frekeunsi, working frequency multivibrator circuit with IC 555 is determined by the configuration value R10K, R56K and C0.01uF. To change the alarm tone generated a series of light is the value of R and C may be changed as desired.