Mutchus

Circuit Diagram Description This is a circuit which sounds on the momentary breaking up of a guard circuit comprising a magnet and a reed switch a small permanent magnet is fitted at the edge of the door to be guarded, a normally open reed switch is fitted on the door frame or a wall facing the magnet. In the normally closed condition of the door, the reed switch is very close to the magnet and hence the reed contact is kept closed. When the door is opened the reed switch contact opens. This triggers a scr, the gate of the scr is connected to its cathode through the reed switch. As long as the switch is closed, the scr dose not fire, but when the door is opened the switch also opens and the scr fires, supplying voltage to the alarm. Engineers note: This alarm looks so simple but it is more effective and fool proof the audio signals can further be amplified according to the area or the place it is fixed and the major plus point is that even if the door is closed after opening or in ca...

Here is a simple, low-cost intruder detector that uses an invisible laser beam to detect the intruder. The laser beam is produced using a 3V DC or 4.5V DC laser pointer or torch that is available in the market. The 3V DC or 4.5V DC power supply for the laser transmitter can also be given using a bridger ectifier or full-wave rectifier. Fig. 1 shows the block diagram of the complete unit comprising the transmitter and receiver sections. The laser beam from the transmitter after reflection from various mirrors (M1 through M6, as shown in Fig. 1) is made to fall on the photodetector in the receiver circuit. Fig. 1: Block diagram of intruder detector using laser torch Once the laser beam is positioned, the receiver circuit is powered by closing switch S. An alarm unit operating on 230V AC is connected to the relay RL in the receiver circuit. When an intruder interrupts the path of the beam or switches off the laser torch, the alarm unit becomes activated. The alarm unit remains activated u...