Project Hub /Artificial Intelligence & Edge ML/Gesture Recognition/Over-Heat Detector

Intermediate

ANALOG / DISCRETE

< ₹500

3 – 6 Hours

Partial Kit

Over-Heat Detector

Q: Why is an NTC thermistor used instead of a PTC thermistor?

An NTC (Negative Temperature Coefficient) thermistor decreases in resistance as it gets hotter, making it straightforward to configure a voltage divider that yields an increasing voltage signal as temperatures rise toward a danger zone.

Q: What is the purpose of the potentiometer VR1?

Potentiometer VR1 allows you to manually adjust the reference voltage fed into the LM358 op-amp, effectively letting you calibrate the exact temperature threshold at which the relay will trip.

Q: Do I need to write any software or code for this project?

No, this is a purely analog hardware circuit utilizing discrete components and an operational amplifier, so no programming or microcontroller is required.

An over-heat detector circuit utilizing a 10k negative temperature coefficient (NTC) thermistor and an LM358 operational amplifier to trigger a relay when temperature limits are exceeded.

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.

5V 1 Channel Relay Module Rs. 45.00
10pcs - 220 ohm 1/4 W Resistor Set Rs. 39.00
400 Points Mini Solderless Prototype PCB Breadboard High Quality Rs. 89.00
MB102 Adjustable Breadboard Power Supply Module (3.3V & 5V) for Arduino & Raspberry Pi Rs. 139.00
Jumper Wire 10 Pin Male To Male 20cm Rs. 45.00
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: LM35 / Analog Temp Sensor
Potentiometer / Trimpot
Transistors (BC547 / 2N2222 / TIP / MOSFET)
Capacitors
Custom PCB / PCB Fab
12V 1C

Browse all components

How It Works

The Over-Heat Detector project operates by monitoring temperature changes using a 10k negative temperature coefficient (NTC) thermistor, whose electrical resistance decreases as its temperature increases. This thermistor is configured in a voltage divider network, supplying an analog voltage signal that varies with temperature to one input of an LM358 dual operational amplifier IC. The second input of the op-amp is connected to a potentiometer (VR1), which acts as a manual reference voltage adjuster to set the precise temperature threshold required for triggering the circuit. When the temperature rises to a point where the thermistor's voltage drops past the set reference voltage, the LM358 changes its output state from low to high. This output current is amplified by an NPN transistor, which acts as an electronic switch to drive the 12V 1C/O relay coil. Once energized, the relay mechanically switches its contacts, allowing external equipment or alarm systems to be turned on or off to prevent thermal damage.

Why Build This

Design a reliable, microcontroller-free thermal protection circuit suitable for industrial control panels and motor management systems.

Gain practical experience implementing analog sensor conditioning using NTC thermistors and adjustable comparator circuits.

Learn how to interface low-voltage analog control electronics with higher-power electromechanical relays for automated load switching.

Real-World Application

Temperature monitoring and thermal protection in electronic devices, industrial panels, appliances, and motor control systems to prevent overheating damage.

Skills You'll Learn

analog sensor interfacing

operational amplifier comparator design

voltage divider configuration

transistor switching stages

relay driver implementation

Safety Precautions

Ensure proper wiring when connecting mains-powered loads to the relay switch to avoid electrical shock.

Technology Tags

NTC THERMISTOR

LM358

OP-AMP

RELAY

ANALOG CIRCUIT

TEMPERATURE SENSOR

PCB DESIGN

Frequently Asked Questions

Why is an NTC thermistor used instead of a PTC thermistor?

An NTC (Negative Temperature Coefficient) thermistor decreases in resistance as it gets hotter, making it straightforward to configure a voltage divider that yields an increasing voltage signal as temperatures rise toward a danger zone.

What is the purpose of the potentiometer VR1?

Potentiometer VR1 allows you to manually adjust the reference voltage fed into the LM358 op-amp, effectively letting you calibrate the exact temperature threshold at which the relay will trip.

Do I need to write any software or code for this project?

No, this is a purely analog hardware circuit utilizing discrete components and an operational amplifier, so no programming or microcontroller is required.

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-00178

Over-Heat Detector

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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