Project idea: Build a priority-based automatic transfer unit that monitors four source-availability inputs and switches a lamp load to the highest-priority available source using 8051 logic, relay drivers, and safety-isolated relay channels.
 
Project description: The AT89S52 reads four switches indicating source presence, updates a 16x2 LCD with the active source, and energizes the matching relay via ULN2803 to connect the load, cascading to the next source if a higher-priority source fails.
Relay selection uses standard 12 V sugar-cube or power relays on PCB terminals, while a 7805 regulator supplies 5 V to MCU and display from the low-voltage rail.
Specifications
 
Hardware:
8051 MCU (AT89S52),
11.0592 MHz crystal,
ULN2803 relay driver,
12 V relays, 16x2 LCD,
7805 regulator,
DIP sockets,
LEDs,
push buttons,
screw terminals,
PCB/breadboard,
lamp load, and wiring.

Software: Keil µVision toolchain with Embedded C for 8051 families and peripheral drivers (GPIO, LCD, timing).
 
Features:
Automatic, priority-based source switching across four inputs with relay isolation for safe AC handling.
Live LCD indication of active source and simple tactile-switch fault simulation for demos and testing.
 
Applications:
Backup supply management for labs, kiosks, classrooms, and benches where no-break demonstration is essential.
Educational platform to learn 8051-based control, LCD interfacing, and relay driver design with inductive load protection.
 
Dimensions
Proposed build (electronics baseplate): 20 × 15 × 7 cm, allowing space for an AT89S52 board (~10.5 × 9.2 cm) and a 16x2 LCD.
Designed spacing supports safe routing between low-voltage control and high-voltage relay side for demos.
 
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.
 
Shipping dimensions
Packed unit with cushioning: 25 × 20 × 12 cm to accommodate baseplate, bulb, and cabling.
Box sizing considers anti-static and shock protection for the LCD and relay assemblies.
 
Weight:
Estimated net weight: 2 kg including board, relays, LCD, wiring, and a 230 V bulb.
The bulb alone can contribute a few hundred grams, so packing weight varies with lamp type.
 
Notes: All the products are made by LearnElectronics India and not for re-sale.