Project Hub /Healthcare Biomedical & Assistive/Bio-signal Acquisition (ECG/EMG/EEG)/Humidity Controller and Indicator

Intermediate

ANALOG / DISCRETE

Project Specific

3 – 6 Hours

Partial Kit

Humidity Controller and Indicator

A simple hardware circuit utilizing the SY-HS-220 humidity sensor and LM3914 driver to monitor and control relative humidity levels between 30% and 90%.

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.

DHT11 Temperature and Humidity Sensor Module for Arduino Raspberry Pi Rs. 89.00
5V 1 Channel Relay Module Rs. 45.00
10pcs 5mm RED Diffused Light Emitting Diodes - LEDs Set Rs. 39.00
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: Passive Components (generic)
Microcontroller IC (DIP) / Chip
Transistors (BC547 / 2N2222 / TIP / MOSFET)
LM3914 Dot

Browse all components

How It Works

The Humidity Controller and Indicator circuit is designed to monitor relative humidity levels ranging from 30% to 90% and take action when thresholds are crossed. At the heart of the system is the SY-HS-220 humidity sensor, which senses ambient moisture in the air and converts it into a varying electrical signal. This analog signal is processed by the LM3914 dot/bar display driver IC. The LM3914 takes the input voltage and illuminates a sequence of LEDs (LED1 through LED7) to visually represent the current humidity level on a scale. To allow for precise calibration, a 10-kilo-ohm preset potentiometer (VR1) is included, letting you adjust the sensitivity and set specific trigger points for the display and control mechanisms. When the humidity reaches a predetermined threshold, the circuit activates transistors T1 and T2, which act as relay drivers. These transistors provide the necessary current amplification to switch the relays on or off, allowing the system to control external devices such as humidifiers or dehumidifiers to maintain the desired atmospheric conditions.

Why Build This

Gain practical experience building analog environmental monitoring systems without needing complex microcontroller programming.

Understand how sensor signals can be visually displayed using dot/bar driver ICs like the LM3914.

Learn how to use transistor driver stages to interface low-power sensor circuits with electromechanical relays for real-world device control.

Real-World Application

Used in fabric and textile industries where maintaining precise relative humidity (RH) levels is critical for managing material properties like tensile strength, elasticity, and fiber diameter.

Skills You'll Learn

Analog sensor interfacing

LED driver configuration

potentiometer calibration

transistor relay driving

environmental monitoring hardware design

Safety Precautions

No specific precautions noted for this build — always follow general electronics safety practices.

Technology Tags

HUMIDITY SENSOR

SY-HS-220

LM3914

LED DISPLAY

ANALOG CIRCUITRY

RELAYS

TRANSISTORS

Frequently Asked Questions

Do I need to write any programming code for this project?

No, this is a purely analog and discrete hardware project, so no software or programming is required.

What is the purpose of the 10-kilo-ohm preset (VR1)?

VR1 is used to calibrate the circuit's sensitivity, allowing you to fine-tune how the LM3914 driver responds to inputs from the SY-HS-220 humidity sensor.

What do transistors T1 and T2 do in the circuit?

T1 and T2 act as relay drivers, providing the necessary current boost from the sensor and driver stage to safely switch the electromechanical relays on and off.

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-00227