MULTITONE ALARM CIRCUIT SCHEMATIC DIAGRAM

MULTITONE ALARM CIRCUIT SCHEMATIC DIAGRAM
The two op amps inside the MC 1458 are used to produce square and triangular waves. LM 380 is used to amplify the output. The first op amp IC1a is wired as an astable multi vibrator and second op amp IC1b is wired as an integrator, to make the square wave triangle.

The two output square ans sine can be selected using switch S1 to the input of IC2 which amplifies it to drive the speaker. POT R4 can be used for tone adjustment.

EMERGENCY LIGHT AND ALARM SCHEMATIC DIAGRAM

EMERGENCY LIGHT AND ALARM SCHEMATIC DIAGRAM

This circuit is permanently plugged into a mains socket and NI-CD batteries are trickle-charged. When a power outage occurs, the lamp automatically illuminates. Instead of illuminating a lamp, an alarm sounder can be chosen.

When power supply is restored, the lamp or the alarm is switched-off. A switch provides a “latch-up” function, in order to extend lamp or alarm operation even when power is restored.

DOOR KNOB TOUCH ALARM SCHEMATIC DIAGRAM

DOOR KNOB TOUCH ALARM SCHEMATIC DIAGRAM
The alarm will be activated when someone touch the metal door knod. This circuit won’t work on full metal door.

SAFER SECURITY SYSTEM ALARM CIRCUIT SCHEMATIC DIAGRAM

SAFER SECURITY SYSTEM ALARM CIRCUIT SCHEMATIC DIAGRAM

Step 1 is to translate the loop resistance into a voltage; that’s done by putting it into a voltage divider with resistors R1 and R2. Capacitor C2 protects the circuit against electromagnetic noise-important because burglar alarms use long wires, often running near heavy electrical equipment.

Step 2 is to translate the voltage into a logic signal indicating whether it’s in resisthe correct range. That’s where the LM3915 comes in. Normally, the LM3 9 15 would drive ten LEDs, one for each of ten small ranges of voltage. To obtain logic-level outputs, we have it driving 1K resistors instead of LEDs. Since we only need to distinguish three situations, not ten, we tie some of the outputs together. The LM3915 has open-collector outputs that can be paralleled in that way.