Intermediate
ANALOG / DISCRETE
Project Specific
3 – 6 Hours
Automatic Hand Wash Timer
A simple and low-cost automatic hand-wash timer using an NE555 timer in monostable mode and an FC-51 IR sensor to ensure a 20-second handwashing duration.
Originally published by Shashank T.S. on ElectronicsForU
View original tutorial
How It Works
The Automatic Hand Wash Timer is built around an NE555 timer IC configured in monostable mode, partnering with an FC-51 infrared sensor module to promote proper hand hygiene. When a user approaches the washbasin, the FC-51 IR sensor detects the presence of hands by emitting infrared light and reading the reflection. This detection triggers the trigger pin of the NE555 timer IC. Upon being triggered, the NE555 transitions its output state to high for a predetermined duration calculated by the timing components, specifically resistor R3 and capacitors such as the 100uF C2/C3 timing capacitor. While the output remains high, it drives an LED (LED1) and a buzzer to provide a continuous visual and audible cue. This signals the user to continue scrubbing their hands for the required 20-second interval. Once the RC time constant expires, the NE555 output automatically drops back to a low state, turning off the buzzer and LED1 to indicate that the hand-washing cycle is complete. Power is supplied to the entire circuit via a dedicated power supply, with all components neatly soldered onto a veroboard or general-purpose PCB using connecting wires.
Why Build This
Promote proper hygiene habits in school restrooms or community spaces by enforcing a reliable 20-second handwashing duration.
Build a touchless activation system using infrared sensing to prevent the spread of germs on high-touch surfaces.
Apply analog electronics principles like RC timing and sensor integration to create a practical, real-world gadget.
Real-World Application
Public and residential washbasins to enforce proper hand hygiene duration without touching germ-prone surfaces.
Skills You'll Learn
Monostable multivibrator circuit design
infrared proximity sensor integration
RC timing configuration
analog circuit assembly on veroboard
audio-visual feedback implementation
Safety Precautions
No specific precautions noted for this build — always follow general electronics safety practices.
Ready to build this?
We stock the boards, sensors and modules this project needs. A full parts list is coming soon — for now, browse our DIY Kits & components or search for Analog / Discrete parts.
Frequently Asked Questions
Why is an NE555 timer configured in monostable mode for this project?
In monostable mode, the NE555 acts as a one-shot pulse generator. When triggered by the IR sensor, it keeps the buzzer and LED active for a fixed duration determined by the timing capacitor and resistors before automatically turning them off.
Can I adjust the washing time from 20 seconds to a different duration?
Yes, you can alter the time duration by changing the values of the timing components, such as the 100uF capacitor (C2/C3) or resistor R3, since the time delay depends directly on the RC time constant.
Do I need any programming or microcontroller knowledge to build this?
No, this is a purely hardware-based analog circuit. There is no software or microcontroller required; the logic is handled entirely by the NE555 timer IC and discrete components.
Gallery
Kitkraft Project Hub — curated from the maker community, credited at the source.
PRJ-00288