Description.

Here is the circuit diagram of a magnetic proximity switch that finds a lot of applications in many fields.The circuit is based on a magnetic reed switch(S1) as the proximity sensor. A monostable multivibrator based on NE555 (IC1) and a toggle flip flop based on CD4013 (IC2) does the rest of the circuit.

When a magnet is reached in proximity of S1 it closes to give a negative trigger at pin 2 of IC1.The output of IC1 goes high for a time determines by R2 and C2.This clocks the IC2 wired as a toggle flip flop.The output (pin 1 ) of IC2 goes high and the transistor Q1 is biased to ON.The relay is activated and so do the equipment connected to the relay.The LED D1 glows when IC1 is triggered.

Circuit diagram with Parts list.

Notes.

• Switch S1 can be a general purpose magnetic reed switch.
• The equipment to control can be connected using NC,NO and C points of the relay according to the application.
• Use a 12 regulated power supply for powering the circuit.

Description.

When there is a fire breakout in the room the temperature increases.This ultra compact and low cost fire alarm senses fire breakout based on this fact.

Transistor BC177 (Q1) is used as the fire sensor here.When the temperature increases the leakage current of this transistor also increases.The circuit is designed so that when there is an increase in the leakage current of Q1 ,transistor Q2 will get biased.As a result when there is a fire breakout the transistor Q2 will be on.The emitter of Q2 (BC 108)is connected to the base of Q3(AC 128).So when Q2 is ON Q3 will be also ON.The transistor Q3 drives the relay which is used to drive the load ie,light,bell,horn etc as an indication of the fire.The diode D1 is used as a free wheeling diode to protect it from back EMF generated when relay is switched.

Circuit diagram with Parts list.

Notes.

• The Preset R1 can be used to desired temperature level for setting the alarm ON.
• This is not a latching alarm,ie;when the temperature in the vicinity of the sensor decreases below the set point the alarm stops.
• The circuit can be powered using  a 9V battery or a 9V battery eliminator.
• All capacitors are electrolytic and must be rated at least 10V.
• The load can be connected through the C,NC,NO points of the relay according to your need.
• The calibration can be done using a soldering iron,and a thermo meter.Switch ON the power supply.Keep the tip of soldering iron near to the Q1.Same time also keep the thermometer close to it.When the temperature reaches your desired value adjust R1 so that relay gets ON.Done!

Description

This is a simple proximity detector using IC CS209. The CS209A is a bipolar monolithic
integrated circuit for use in metal detection/proximity sensing applications.The
CS209A contains an oscillator set up by an external parallel resonant tank and a feedback resistor connected between pin 2 & 3 .The internal oscillator operates close to the resonant frequency of the tank circuit.As a metal object is brought close to the inductor,
the amplitude of the voltage across the tank gradually begins to drop. When the envelope of the oscillation reaches a certain level, the IC causes the outputs to toggle states.potentiometer connected between pin 1 & 8 is adjusted to achieve a certain detection distance range. The larger the resistance the greater the trip-point
distance.Detection range can be incresed by using a high Q coil.Maximum possible range is 1 inch with a  well tuned  circuit.Only difficulty in making this  circuit is the tuning up the circuit to a particular range.For making it easy place a metal piece at the desired distance from coil (with in 1 inch) and adjust resistance Rf to make one of the outputs (  pin4 or 5) to change state.
Circuit Diagram