Project Hub /Security Surveillance & Defense/Intrusion Detection Systems/Motion Activated Tap Water Flow Circuit

Intermediate

ANALOG / DISCRETE

Project Specific

3 – 6 Hours

Partial Kit

Motion Activated Tap Water Flow Circuit

Build a motion-activated water tap controller using a PIR sensor and solenoid valve to automatically manage water flow and prevent wastage.

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.

PIR Motion Detector Sensor Module HC-SR501 Rs. 153.00
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: Battery (generic / unspecified)
DC Barrel Jack / Power Connector
Transistors (BC547 / 2N2222 / TIP / MOSFET)
Solenoid / Electric Lock
Diodes (1N4007 / 1N4148 / Schottky / Zener)
Header Pins / Terminals / Connectors
Perfboard / Veroboard / Stripboard
Enclosure / Box / Case
2-pin terminal

Browse all components

How It Works

The Motion Activated Tap Water Flow Circuit is an analog intrusion-detection and automation system designed to control fluid delivery based on physical presence. Power enters the circuit through a DC barrel jack (J1) connected to a 12V battery or external 12V DC adapter, distributing power across a general-purpose PCB housed within an enclosure box. An HC-SR501 PIR motion sensor (MS1) continuously monitors the surrounding area for changes in infrared radiation emitted by moving heat sources, such as a user's hands near a sink. When MS1 detects motion, it outputs a positive control signal that travels through a 220-ohm resistor (R1) directly into the base of a BD139 NPN transistor (T1). This base current biases T1 into saturation, causing it to act as a closed electronic switch that completes the circuit path for higher-current loads. With T1 conducting, power is supplied to a 12V normally closed (NC) solenoid valve (SV1) via a 3-pin terminal connector (J2) and a 2-pin terminal (J3). The activation of SV1 opens the internal valve mechanism to permit water flow. To protect the transistor from voltage spikes induced by the inductive coils of the solenoid valve when it de-energizes, a 1N4007 rectifier diode (D1) is placed in parallel as a flyback diode. Once the PIR sensor's dwell time expires and motion is no longer detected, MS1 drops its output signal, turning off transistor T1, which subsequently cuts power to the solenoid valve and halts the water flow.

Why Build This

Design and prototype an automated, touchless water conservation system suitable for commercial sinks, public restrooms, and restaurant kitchens.

Apply undergraduate-level principles of transistor switching theory to interface low-voltage digital sensors with higher-current inductive loads.

Integrate discrete analog components, inductive load protection, and power management circuitry onto a general-purpose PCB housed inside a protective enclosure.

Real-World Application

Automated water conservation systems in public restrooms, restaurants, and commercial sinks.

Skills You'll Learn

Transistor biasing and saturation

Inductive load flyback protection

PIR sensor integration

DC power distribution

Discrete circuit prototyping

Safety Precautions

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

Frequently Asked Questions

Why is a 1N4007 diode included alongside the solenoid valve?

The 1N4007 diode acts as a flyback or freewheeling diode, providing a safe discharge path for the magnetic voltage spikes generated when the 12V solenoid valve turns off, thereby protecting the BD139 transistor from damage.

Can I power this circuit using a standard 5V USB connection?

No, this specific design relies on a 12V DC power source, such as a 12V battery or external 12V DC adapter, to properly energize the 12V NC solenoid valve and drive the HC-SR501 PIR sensor.

What is the role of the BD139 transistor in this setup?

The HC-SR501 PIR sensor cannot supply enough current to directly drive the solenoid valve. The BD139 NPN transistor acts as an electronic switch, using the low-current signal from the sensor to control the high-current path required by the valve.

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.

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