Project Hub /Basic Analog & Power Electronics/Battery Chargers & Charging Circuits/DIY BCD Watch

Intermediate

ARDUINO

₹500 – ₹1,500

3 – 6 Hours

Partial Kit

DIY BCD Watch

A unique wearable binary coded decimal (BCD) watch powered by an ATtiny85 microcontroller and a 74HC595 shift register, displaying time in binary format using LEDs.

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.

10pcs 5mm RED Diffused Light Emitting Diodes - LEDs Set Rs. 39.00
2-Slot 18650 Holder with Protective Cover and On/Off Switch – Case Rs. 109.00
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

We don't carry yet: Battery (generic / unspecified)
ATtiny
Logic ICs (74xx / 40xx)
Battery Charger Module TP4056
Custom PCB / PCB Fab
Watch Strap
Voltage Divider Components

Browse all components

How It Works

The DIY BCD Watch operates as a wearable digital timekeeping device controlled by an ATtiny85 microcontroller. Because the ATtiny85 has a limited number of input/output pins, the circuit utilizes a 74HC595 shift register to expand the microcontroller's output capability, enabling it to drive multiple LEDs without running out of pins. The time is displayed using Binary Coded Decimal (BCD) format across these LEDs, representing hours and minutes through combinations of illuminated lights rather than standard numeric digits. A push button allows the user to interact with the device, such as waking the display to check the current time. Power is supplied by an integrated battery, regulated for safe operation via voltage divider components that also allow the microcontroller to monitor the system's power levels. To maintain continuous operation, a TP4056 IC manages the battery charging cycle, ensuring that the connected lithium-based power source can be safely replenished via a standard power input. The entire custom electronic circuit is housed compactly on a custom round PCB designed to fit comfortably onto a physical watch strap for daily wear.

Why Build This

Deepen your undergraduate engineering understanding of digital logic and binary number systems through hands-on wearable implementation.

Practice efficient pin-expansion techniques using shift registers with resource-constrained microcontrollers like the ATtiny85.

Design and integrate power management circuitry, including linear charging and voltage monitoring, into a miniaturized wearable form factor.

Real-World Application

Custom wearable technology, educational demonstration of binary number systems, and unique conversation-piece accessories.

Skills You'll Learn

Shift register interfacing

Binary Coded Decimal logic implementation

Microcontroller pin-expansion techniques

Battery charging circuit integration

Low-power wearable system design

Safety Precautions

Ensure correct polarity when connecting the battery to prevent short circuits or damage to the TP4056 charging IC and ATtiny85 microcontroller.

Technology Tags

ATTINY85

74HC595 SHIFT REGISTER

TP4056

ARDUINO IDE

PCB DESIGN

BINARY NUMBERS

WEARABLE ELECTRONICS

Frequently Asked Questions

How do I read the time on a BCD watch?

A Binary Coded Decimal watch displays numerical digits using rows or columns of binary-weighted LEDs (typically representing powers of two like 1, 2, 4, and 8), which you add together to read the hours and minutes.

Can I program the ATtiny85 using the standard Arduino IDE?

Yes, by installing the ATtiny85 board package into the Arduino IDE, you can write your code on a computer and upload it directly to the microcontroller.

How is the battery charged safely on this custom board?

The onboard TP4056 IC manages the constant-current and constant-voltage charging cycle for the connected battery, protecting it from overcharging when connected to a power source.

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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