Doorbell for Deaf People.
When a deaf person is alone in a house, it would be very difficult to realize that someone is knocking on the door without any visual warning signal.
The main component for the Doorbell for the deaf circuit is the CMOS 4001 integrated circuit, which has four two input NOR gates
Car Burglar Alarm using two 555 timers
This is a simple Car Burglar Alarm circuit that uses a dual contact relay and two 555 timers, each of them working as a monostable multivibrator.
The alarm will activate the car horn, approximately 5 seconds after either door is opened and has not been properly closed.
Power failure alarm using transformer and relay
This power failure alarm circuit is very simple and is very useful when used with electric ovens, a refrigeration systems or to prevent a thief from cutting off the electrical power because it immediately warns of the problem. It also serves you when the fuses have blown.
This light sensitive alarm is very simple and works using, as main components, a transistor, an LDR and a relay.
The 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.
