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Arduino project · Temperature and climate · Easy

Hotter Room Indicator (Two Sensors)

Two temperature sensors compare two rooms. The red LED shows room 1 is warmer; the blue LED shows room 2 is warmer.

What you will learn

  • How to compare two measurements
  • Why a margin avoids flicker
  • How heat flows between rooms

How it works

Each LED lights when its room is warmer by more than 2 degrees. If they are about equal both stay off. The Compare step checks one sensor against another, so you do not need to set a fixed number.

Try this next

  • Start a fan in the warmer room.
  • Show both temperatures on an LCD.
  • Log the difference with an SD card.

The simulator program and explanation on this page are original. The idea follows a classic Arduino project that students have built for years.

1Choose your Arduino board
2Build the circuit
Parts: sensors and actuators (tap to show or hide)

Try the inputs (virtual sensors)

Pins (you can change them)

PartArduino pin (change it here)How to wire it

Every wire, one by one

Red rail = 5 V from the Arduino 5V pin. Black rail = GND. The coloured wires carry signals. Match the wire colours on the drawing to this list.

#ColourFrom (part and leg)To
3Define the sequence

Steps run from top to bottom, then start again. While the simulation runs, the active step is highlighted in green.

4Arduino code





5Parts list and where to buy


Quantities come from the parts you added. The store links open a search for that item on Robu.in, Amazon.in and ThinkRobotics, so you always see what is in stock today. Check the model, voltage and price before you order.


#ItemQtySearch termBuy / compare



6Export








The PDF has the circuit sketch, pin table, every wire, sequence, full code, the parts list with store links, do’s and don’ts for each part, and the safety notes. The project file lets you come back and keep editing.



7Learn: do’s, don’ts, cautions and tips





In the real world
Which room is hotter?
Compare two rooms. The red lamp marks the hotter one, the blue lamp the cooler one.
Tip: use the gold tab at the bottom of the circuit drawing to pull the real-world view up over the Arduino board. Your parts stay visible above it, so you can press a button and watch the real scene react.