Magnetic Proximity Switch Sensor Circuit

Magnetic Proximity Switch Sensor Circuit can feel magnetic field.

It is used in factory, security and automation.

Main part is magnetic reed switch as sensor.

ICs like 555 timer and CD 4013 flip-flop turn relay ON/OFF when magnet is close by.

Relay control other device ON/OFF.

Circuit need stable 12V power for good working.

Circuit Working:

Parts List:

When magnet is near S1 then switch closes and circuit starts.

IC1 555 works as monostable and makes one pulse when S1 is pressed.

IC2 CD 4013 flip-flop changes state on each pulse from IC1.

Q1 BC547 works like switch to control 12V SPDT relay.

LED1 shows magnetic field found and relay working.

When pulse end IC1 output goes low and LED goes OFF.

D1 1N4007 stops relay coil spikes from damaging the circuit.

Formulas with Calculations:

IC1 555 pulse time:

T = 1.1 * R2 * C2

where,

• R2 is 470k
• C2 is 2.2µF
• T is 1.1 * 470000 * 2.2×10⁻⁶ = 1.1374 s = 1.14 s.

So 555 output is HIGH to about 1.14 seconds per trigger.

Q1 base current:

Ib = (Vin – VBE) / R4

where,

• Vin is 12V
• VBE IS 0.7V
• R4 is 2.2k.
• Ib = (12 – 0.7) / 2200 = 0.005136 A = 5.14 mA.

Transistor gain is 200 hFE.

So collector current is plenty enough to drive the relay.

How to Build:

To build a Magnetic Proximity Switch Sensor Circuit following steps are needed to be followed for designing our own circuit:

• Put all parts like the circuit diagram.
• Assemble parts on board.

IC1 555:

• Pin 1 connect to GND.
• Pin 2 connect between R3 and S1.
• Pin 3 connect to pin 3 of IC2.
• Pin 4 and pin 8 connect to +12V.
• Pin 5 connect to GND through C1.
• Pin 6 connect to pin 7 of IC1.
• Positive of C2 connect between pin 6 and GND.
• R2 connect between pin 7 and +12V.

LED and R1:

• One end of R1 connect between IC1 pin 3 and IC2 pin 3.
• Other end of R1 connect to LED anode.
• LED cathode connect to GND.

IC2 CD 4013:

• Pin 1 connect to base of Q1 through R4.
• Pins 4, 6, 7, 8, 9, 10 and 11 connect to GND.
• Pin 2 connect to pin 5.
• Pin 14 connect to +12V.

Transistor Q1 BC547:

• Collector connect to +12V through D1.
• Emitter connect to GND.
• Relay coil connect with one side to collector of Q1 and the other side to +12V.

Diode D1:

• D1 connect across the relay coil cathode to +12V and anode to Q1 collector to stop spikes.

Conclusion:

Magnetic Proximity Switch Sensor Circuit detects magnet and flips relay using 555 timer and CD 4013.

BC547 drives the relay, LED shows detection and 12V supply keeps circuit stable.

This circuit is useful for security, automation and smart control.

References:

CD4013B CMOS Dual D-Type Flip-Flop