Project idea
Build an 8051-based phase-angle controller that senses AC zero crossings and triggers a pair of SCRs at a programmable firing delay, so the delivered power to an AC load can be increased or decreased using push buttons; for demonstration, a lamp is used as a safe proxy for an induction motor’s power variation effect on speed/torque slip.
 
Project description
A zero-crossing detector interrupts the AT89C51-class microcontroller every half-cycle; the firmware produces a variable delay (0–~9 ms at 50 Hz) before issuing isolated gate triggers to the anti-parallel SCR pair via opto-triac drivers, thereby controlling the phase angle and the RMS power to the load.
Increment/decrement switches adjust the firing angle in steps, and a mains lamp visually indicates power modulation that corresponds to the motor’s power input in a lab-safe manner for demonstration.
 
Components
8051 development board (AT89S52)
LM393 dual comparator
MOC3021 opto-triac driver IC
SCR C106MG thyristor
12V 500mA step-down transformer
LM7805 5V linear regulator
Single-phase bridge rectifier 
Tactile/push-button switches
230V, 100W incandescent lamp (demo load)
 
Features
Phase-angle control of AC power using zero-cross detection and delayed firing, covering a wide usable range across the half-cycle.
Opto-isolated gate drive for line-mains safety and reliable triggering of controlled devices.
Push-button adjustment for increasing or decreasing the delivered power in consistent steps.
Demonstration-friendly lamp load showing visible intensity change correlated to power variation.
 
Applications
Lab demonstration of AC power control and firing-angle modulation principles.
Educational prototype for induction motor power/speed control concepts via voltage-phase control.
Dimmable lighting and heater power regulation training systems.
 
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)
Assembled trainer-style build typically arranged on a small base near the transformer footprint; transformer size reference: 6.3 × 3.3 × 3.3 cm, guiding a compact assembly target in the ~12 × 10 × 6 cm class.
 
Shipping dimensions (cm)
Boxed kit packaging commonly targets protective clearance around small dev boards and a transformer; a practical small parcel format is approximately 20 × 15 × 10 cm.
 
Weight
An 8051 dev board listing indicates about 150 g for the board alone, with total kit mass dependent on transformer and power components.
 
Estimated project weight: 1kg
 
Notes: All the products are made by LearnElectronics India and not for re-sale.