“Temperature sensor relay switching circuit”

SARKER, A.S.M. IMRUL HASAN BARAI, AVIJIT GHOSH, SREEKOR KHAN, TAHMID RAHMAN, JILLUR NISHAT, FARHA FARZANA List names of students involved Under the supervision of shuvra saha

Introduction Theory: Relays are electromechanical devices that use an electromagnet to operate a pair of movable contacts from an open position to a closed position. The electro-mechanical relay is an output device (actuator) which come in a whole host of shapes, sizes and designs, and have many uses and applications in electronic circuits. But while electrical relays can be used to allow low power electronic or computer type circuits to switch relatively high currents or voltages both “ON” or “OFF”, some form of relay switch circuit is required to control it.

List of components: 1. LM35: The LM35 series are precision integrated-circuit temperature devices with an output voltage linearly-proportional to the Centigrade temperature. 2. OPAMP: An operational amplifier is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output.

List of components: 3. Transistor: A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power 4. Diode: A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other.

List of components: 5. Relay: A relay is an electromagnetic switch operated by a relatively small electric current that can turn on or off a much larger electric current.

Software Used: Proteus Design Suite: A proprietary software tool suite used primarily for electronic design automation. A Windows application for schematic capture, simulation, and PCB (Printed Circuit Board) layout design. All PCB Design products include an auto router and basic mixed mode SPICE simulation capabilities. Developed in Yorkshire, England by Labcenter Electronics Ltd.

Working principle: The operating voltage range of this LM35 ranges from-55˚ to +150˚C and it has low-self heating. This is operated under 4 to 30 volts. The most extensively used electronic devices are operational amplifiers, which are certain kind of differential amplifiers. Temperature sensor circuit has terminals such as two inputs like non-inverting (+) and inverting (-) and only one output pin. Operational amplifier IC741 is used as a non-inverting amplifier. The variation between the i/p terminals amplifies the circuit.

The amount produced by IC amplifies in an amount to the temperature by 10 mV per degree. This unstable voltage is supply to a comparator IC 741. We have used IC741 as a non-inverting amplifier which means pin-3 is the input and the output is not inverted. This LM35 temperature sensor circuit amplifies the difference between its input terminals. Output of IC741 connected with the base of BJT to relay. If the temperature(fixed by threshold voltage) more than 27 degree, the 12v relay will be turned on and the LED will glow. Working principle:

Circuit Diagram: (Proteus)

Simulation: ( 26 degree, Relay OFF )

Simulation: (27 degree, Relay ON )

Hardware Implementation: 1. Taking Printout of PCB Layout. 2. Cutting the Copper Plate. 3. Making It Smooth. 4. Ironing on Glossy paper. 5. Peeling 6. Etching 7. Cleaning 8. Drilling Holes on the PCB 9. PCB Assembly

PCB Layout Design: Top silk:

PCB Layout Design: Bottom copper

PCB Layout Design: 3D view (Top):

PCB Layout Design: 3D view (Bottom):

Applications HVAC Systems Power Supplies Water Tanks Freezers Battery Management Systems Industrial Applications like Boilers, steamers, chillers etc.

Discussion & conclusion: Iron on Glossy paper method is efficient method to make PCB at home. If done carefully each track can be perfectly printed. Circuit by hand on PCB is limited to our artistic skills. Simple circuit can easily be made by this method but for complex PCB Iron on Glossy paper is best.

References:  switch-circuit-diagram switch-circuit-diagram  circuit.html circuit.html  switch-pin-diagram switch-pin-diagram   1)/Proj-03.html 1)/Proj-03.html