I built a free automated bell system for schools using Python and a $6 USB relay — here's how and why

SaSiEzhilmani — Sat, 02 May 2026 07:58:48 +0000

The Problem I Watched Every Day

I am Ezhilmani — System Administrator from
Tamil Nadu, India.

Every single working day I watched a staff member
walk to the school bell, ring it manually, walk back.

Ten times a day. Every working day.

One missed ring meant late classes.
One wrong timing meant confusion across the campus.
It was 2026 and we were still doing this by hand.

I decided to fix it.

What I Built

SaSiE Bell System — a free, open source Windows
desktop application that automates school bell
scheduling completely using Python and a $6 USB
HID relay module.

No expensive hardware. No proprietary software.
No monthly subscription. Just Python and a
₹500 relay module connected to your existing bell.

Tech Stack

Python 3.8+
Tkinter — GUI
HID library — USB relay control
Pillow — logo/image display
JSON — schedule storage

Hardware: USB HID Relay Module

Vendor ID: 0x16C0
Product ID: 0x05DF
Cost: approximately ₹500 / $6

Key Features

Scheduling

Set bell times in HH:MM format
Multiple named schedules — Regular Day, Exam Week, Special Events
Smart mid-day start — skips past bells automatically when app opens mid-session
30-second on-screen countdown warning before every bell

Hardware Control

USB HID relay — direct Python control
Customisable bell duration 1 to 9 seconds
Manual override — ring bell anytime, available even without login

Security

Dual password system — Admin and User roles
Session-based — no re-prompting once logged in
Guest mode — only manual bell visible, everything else locked behind overlay

Logging

Every bell ring logged with date and time
View, clear, or auto-clean logs older than 7 days

Customisation

Institute name and logo in app header
HTML-based header — edit with any text editor
Supports h1 through h6, bold, paragraph tags

The Relay Control Code

The core hardware interaction is surprisingly simple:

import hid

VENDOR_ID  = 0x16c0
PRODUCT_ID = 0x05df

def relay_on():
    device = hid.device()
    device.open(VENDOR_ID, PRODUCT_ID)
    device.send_feature_report([0x00, 0xFF, 0x01, 0x01])
    device.close()

def relay_off():
    device = hid.device()
    device.open(VENDOR_ID, PRODUCT_ID)
    device.send_feature_report([0x00, 0xFD, 0x01, 0x00])
    device.close()

def ring_bell(duration):
    relay_on()
    time.sleep(duration)
    relay_off()

That is it. Three functions.
A ₹500 module. A school bell that now rings itself.

The Smart Scheduler

The most useful technical feature — when you start
the app at 10 AM, it does not ring the 8:30 and
9:30 bells that already passed.

# Pre-mark all past times as already triggered
for time_value, _ in schedule:
    bell_time = datetime.strptime(time_value, "%H:%M")
    if bell_time <= datetime.now():
        triggered_today.add(time_value)

Simple. But genuinely useful in real deployment.

Deployment Results

Deployed at an educational institution
in Tamil Nadu, India.

10 bells automated per day
Schedule: 08:00 AM to 03:00 PM
System uptime: 07:00 AM to 04:00 PM
Previously: fully manual
Result: zero missed bells since deployment

What I Learned Building This

1. Real problems make better software.
Every feature in this app came from watching
a real problem happen in real life.

2. Simple hardware is powerful.
A $6 relay module + Python = full industrial
bell automation. You do not need expensive
proprietary systems.

3. Ship it.
I am a System Admin, not a professional developer.
I built this anyway. It works. It is deployed.
It is helping real people.
That is enough.

Get It Free

Everything is open source under MIT License.
Your name goes on nothing. My name stays on everything.
That is the deal.

🔗 GitHub:
https://github.com/SaSiEzhilmani/SaSiE-BellSystem

If your school or institution is still ringing
bells manually — this is for you.
Any Windows PC. A $6 relay. Done.

Support

If this helped you, a small contribution means a lot.

💳 UPI: sasie@scb
📧 Email: sasiezhilmani@gmail.com
📞 Phone: +91 9092 566 569

Built with Python. Deployed in Tamil Nadu.
Free for every school on earth.

— சசி எழில்மணி (SaSi Ezhilmani / SaSiE)
Tamil Nadu, India 🇮🇳

Cite this work:
SaSi Ezhilmani (SaSiE). SaSiE Bell System.
Zenodo. https://doi.org/10.5281/zenodo.19972626

Forem: SaSiEzhilmani