Project: versatile alarm

Semester: ii

Digital principles

And

system design

Project members:

Hitesh kumar.r2010103011

Rajesh kumar.s.r 2010103534

Skandan 2010103445

Ranganathan 2010103536

VERSATILE ALARM

This project can be used to make five different alarms just by replacing input sensors only. No other changes or adjustments needed in circuit.

1. TOUCH SENSITIVE ALARM2. WATER LEVEL ALARM3. LIGHT SENSITIVE ALARM4. OVER TEMPERATURE ALARM5. MAGNETIC PROXIMITY ALARM

PRINCIPLE

Circuit is wired around popular timer chip 555. It is wired as low frequency astable multivibrator to drive a buzzer and L.E.D. Darlington pair formed by two BC547 transistors used to interfere sensors to alarm circuit. Normally reset pin(pin 4) of 555 timer is held low. So alarm does not sound. But when transistors conduct reset pin is held high. Then alarm is activated. This principle is used here.

TOUCH SENSITIVE ALARM

This project will work as touch sensitive alarm by connecting touch plate to the input of circuit. When touch plates are touched transistors conduct.Then alarm is activated. So it can be used as touch operated calling bell by extending input wires.

WATER LEVEL ALARM

This project can be used as water level alarm by connecting tow probes to input of circuit. Probes may be hanged near top of water tank. When probes are shorted via water or any other conductive liquid alarm will sound.

LIGHT SENSITIVE ALARM

This project can be used as light sensitive alarm by connecting a photo transistor at input. Photo transistor should be connected in correct polarity. At darkness photo transistor does not conduct and alarm is not activated. But when photo transistor(2 leaded) is directed towards and light source(sun light,light bulbs etc) it conducts. As a result alarm is activated.

OVER TEMPERATURE ALARM

This project can be used as over temperature alarm by connecting a reverse biased silicon diode at input of circuit. At room temperature reverse resistance of silicon diode is very high. But when temperature on it increases, its reverse resistance decreases because semiconductors have negative temperature co-efficient of resistance. Here silicon diode should be connected in reverse bias to input of circuit.

MAGNETIC PROXIMITY ALARM

This project can be used as magnetic proximity alarm by connecting a 2 lead reed switch at input. Reed switches are magnet operated type. Normally reed switch terminals are opened. But when a magnet is brought near reed switch its terminals are shorted. Then alarm is activated.

Power supply for the circuit is 9 volts. By adjusting 100K variable resistor, alarm beeping rate can be varied.

APPLICATIONS

Just by changing the inputs, different alarms can be produced which can be used in burglar alarm, photo lighting, touch bell, wake up alarm, rain alarm, sensors in sports fields etc.