Project idea
Build a persistence‑of‑vision display by spinning a narrow PCB “arm” with a row of LEDs and timing their on/off patterns using an ATmega328P to paint digits in the air at HH:MM:SS.
A Hall‑effect sensor and magnet establish zero‑angle sync per revolution, while an HC‑05 Bluetooth link allows Android‑phone time override to instantly correct and update the displayed clock.
 
Project description
An ATmega328P generates LED scan patterns while timers/interrupts schedule column strobes at precise angular positions, driven by a 12 V 775‑class DC motor for stable, high‑RPM rotation to avoid flicker and warping of digits.
A Hall sensor pulse marks index, the firmware maps time to angular columns, and an HC‑05 serial profile lets an Android app send time packets over SPP, enabling immediate HH:MM:SS correction without stopping the rotor.
 
Total list of components
ATmega328P‑PU 8‑bit MCU (DIP‑28).
HC‑05 Bluetooth module (SPP, 9600 baud default).
12 V high‑RPM 775 DC motor (propeller drive).
16×2 character LCD (status on base unit).
16 MHz crystal for MCU clock (HC49/DIP).
7805 linear regulator, TO‑220 (5 V rail).
1N4007 rectifier diode(s) for reverse‑polarity/transient protection.
12 V 2 A DC adapter (SMPS).
A3144 Hall‑effect sensor + small magnet (index sync).
Wiring/connectors and base hardware; rotor PCB with LED row and series resistors; small signal transistors/MOSFETs as LED drivers per current budget (general kit items; see categories referenced for pricing examples).
 
Features
Live HH:MM:SS POV display with crisp digits at stable RPM using a 775‑class motor.
Android time override via HC‑05 SPP to correct time instantly without mechanically stopping the clock.
Hall‑based auto‑index for angular alignment each revolution to keep glyphs steady and readable.
 
Applications
Educational demos of persistence of vision, timing, and motor control in embedded systems labs.
Attention‑grabbing clocks and rotating signage where compact displays are desired.
 
Project Includes:
Fully assembled and tested circuit
Circuit diagram
Source code 
(For DIY KITs - only the components will be provided)
 
Project Types:
DIY KIT(Do IT YourSelf KIT) - We are providing only components in this kit for this project
DIY KIT with Code & Circuit Connections - Along with the components, you will get the Code and the Circuit Connections file to help you build the project easily.
Readymade Breadboard - We are providing fully assembled, tested and ready-made project using plug-n-play jumper wires and breadboard with all the other components, code & circuit diagram.
Readymade Soldered - We are providing fully assembled, tested and ready-made project soldered on a PCB with all the other components, code & circuit diagram.
 
Dimensions (cm)
Typical built unit: base 12 cm× 12cm; rotor arm ~18–20 diameter envelope to clear digits; height ~10, based on compact BT/LCD modules and small bench supply form factors used in hobby builds.
 
Shipping dimensions (cm)
Boxed kit: approximately 25 cm× 20 cm× 10cm(LxWxH) to accommodate motor, base plate, adaptor, and rotor PCB with protective packing, guided by module and accessory shipping sizes shown for similar electronics.
 
Weight
Estimated assembled unit ≈ 0.6–0.9 kg, dominated by the 775 motor, steel hardware, base, and adaptor, with electronics contributing only a few tens of grams (e.g., HC‑05 ≈ 5 g).
 
Estimated project weight (for listing)
List 2 kg to remain conservative for e‑commerce shipping while covering motor and base tolerances.
 
Notes: All the products are made by LearnElectronics India and not for re-sale.