Project Hub /Basic Analog & Power Electronics/Temperature Controlled Switch

Beginner

ANALOG / DISCRETE

< ₹500

3 – 6 Hours

Partial Kit

Temperature Controlled Switch

Q: Do I need to write any code or program a microcontroller for this project?

No, this is a purely analog circuit operating entirely through hardware components like op-amps, comparators, and discrete transistors, so no software is required.

Q: How do I adjust the temperature threshold at which the relay triggers?

You can change the trigger threshold by manually adjusting the potentiometer, which alters the reference voltage fed into the LM358 op-amp comparator.

Q: Can this circuit power high-wattage AC appliances directly?

While the relay acts as a physical switch for external loads, you must respect the current and voltage ratings of the specific relay used and exercise extreme caution with AC mains wiring.

A simple temperature-controlled circuit that triggers automatically when ambient temperature exceeds a preset threshold.

Originally published on ElectronicsForU

View original tutorial

Parts You'll Need

This project is sourced from another site, not written by us — this list is our best match of their components against what we stock, not a verified bill of materials. Always check the original blog (linked above) for the actual parts list before buying.

LM2596 Step Down DC-DC Buck Converter Rs. 99.00
5V 1 Channel Relay Module Rs. 45.00
10pcs - 220 ohm 1/4 W Resistor Set Rs. 39.00
10pcs 5mm RED Diffused Light Emitting Diodes - LEDs Set Rs. 39.00
Jumper Wire 10 Pin Male To Male 20cm Rs. 45.00
MB102 Adjustable Breadboard Power Supply Module (3.3V & 5V) for Arduino & Raspberry Pi Rs. 139.00
400 Points Mini Solderless Prototype PCB Breadboard High Quality Rs. 89.00
Jumper Wire 10 Pin Male To Female 20cm Rs. 45.00

Selected: Rs. 0.00

This list includes a generic resistor set as a placeholder — it is not matched to the exact value or part number this circuit needs. The correct one is specified on the original source page linked above; check it before buying.

We don't carry yet: Diodes (1N4007 / 1N4148 / Schottky / Zener)
Voltage Regulator IC (7805 / LM317 / 1117)
LM35 / Analog Temp Sensor
Capacitors
Potentiometer / Trimpot

Browse all components

How It Works

The Temperature Controlled Switch circuit is an analog automation system designed to activate a connected load (such as a bulb) when the ambient temperature crosses a defined limit. Power is delivered from the 230V AC mains through a step-down transformer to lower the voltage, which is then converted to DC via a bridge rectifier and smoothed with capacitors. A 7805 voltage regulator (IC1) supplies a stable 5V rail for the active components. The core sensing is handled by an LM35 temperature sensor (IC2), which outputs a linear voltage proportional to the ambient temperature in degrees Celsius. This analog voltage signal is fed into an LM358 operational amplifier (IC3). The op-amp acts as a comparator, comparing the sensor's voltage against a reference threshold set by an adjustable potentiometer. When the temperature-dependent voltage from the LM35 exceeds this reference voltage, the op-amp output switches state. This drives the driving stage to energize the 5V single changeover relay (RL1). Once triggered, the relay mechanically switches the heavier load circuit on or off. Visual indicators like LEDs provide status feedback showing power presence and relay activation state, allowing users to monitor the thermal threshold transition in real time without needing software or a microcontroller.

Why Build This

Design and analyze analog sensor conditioning circuits using operational amplifiers and linear voltage regulators.

Implement practical thermal management systems for protecting prototype hardware and enclosures from overheating.

Gain hands-on experience interfacing low-control logic with electromechanical relays capable of switching high-power AC loads.

Real-World Application

Automated thermal management systems, climate control, and overheat protection for equipment.

Skills You'll Learn

analog signal conditioning

operational amplifier comparison

relay interfacing

voltage regulation

power supply design

potentiometer calibration

Safety Precautions

Caution: The circuit works with 230V AC mains electricity. Exercise extreme care while wiring and testing to avoid electric shock.

Technology Tags

LM35

LM358

RELAY

TEMPERATURE SENSOR

POWER SUPPLY

7805

Frequently Asked Questions

Do I need to write any code or program a microcontroller for this project?

No, this is a purely analog circuit operating entirely through hardware components like op-amps, comparators, and discrete transistors, so no software is required.

How do I adjust the temperature threshold at which the relay triggers?

You can change the trigger threshold by manually adjusting the potentiometer, which alters the reference voltage fed into the LM358 op-amp comparator.

Can this circuit power high-wattage AC appliances directly?

While the relay acts as a physical switch for external loads, you must respect the current and voltage ratings of the specific relay used and exercise extreme caution with AC mains wiring.

Gallery

This page is part of Kitkraft's Project Hub — a curated collection of electronics & robotics projects gathered from the maker community to help students and hobbyists discover and learn to build. Kitkraft does not claim authorship of the original project, and makes no representation as to the accuracy, completeness or safety of third-party source material. The summary and "How It Works" explanation above are AI-generated, rewritten with reference to the original tutorial — not a reproduction of it. Full credit and a direct link to the original source are provided above. If you're the original creator and have a concern about how your work is represented here, please contact us and we'll address it promptly.

Kitkraft Project Hub — curated from the maker community, credited at the source.

PRJ-00754

Temperature Controlled Switch

Parts You'll Need

How It Works

Why Build This

Real-World Application

Skills You'll Learn

Safety Precautions

Technology Tags

Frequently Asked Questions

Gallery

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