CD 4047 is the low power Monostable / Astable Multivibrator that requires only an external capacitor and a resistor to give the output pulses. The values of these components determine the output pulse width in the Monostable mode and output frequency in the Astable mode.
CD4047 DATA SHEET

In this flashing led lights circuit, the LDR or photoresistor is connected in such way that when the light intensity varies it will influence the flashing frequency and the brightness of the LEDs.

Unorthodox warning alarm circuit presented here is infact a single chip based general purpose sounder, which produces a pulsed alert tone when its input receives a valid trigger signal. The circuit can be easily interfaced with a number of electronic gadgets and sensors and it requires only 12V dc supply input for proper working. A positive level input at trigger point (J1) activates the warning alarm unit.

This is an Infrared beam breaking alarm ideal to use in entry or passages.It is based on the working of the popular IR sensor Module TSOP 1738 which senses 38 kHz Infrared pulses from the IR LED of the transmitter. Range of the circuit is about 5 meters if the transmitter and receiver are properly aligned
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