Project idea
Design a three-phase solid-state relay by combining three independently controlled single-phase ZVS channels, each built around a TRIAC with an RC snubber and a zero-cross optotriac driver. An 8051 microcontroller generates phase-aligned trigger pulses synchronized to the AC zero crossing for low EMI and reduced inrush on resistive and inductive loads.
 
Project description
An AC zero-cross detector feeds the 8051, which timestamps line zero crossings and issues gate triggers for three opto-isolated triac drivers to achieve near zero-voltage switching on each phase independently. Each phase path uses a power TRIAC, RC snubber, gate resistor, and terminal blocks to interface loads safely, while two push buttons provide manual trigger/pattern inputs with firmware-aligned zero-cross timing. The waveform at the load can be verified on a CRO to confirm ZVS engagement.
 
Total list of components
AT89C51 microcontroller (DIP-40)
40-pin IC socket (DIP-40)
H11AA1 (or equivalent) AC zero-cross optocoupler
MOC3063 (or equivalent) zero-cross optotriac driver × 3
BTA16-600 (or equivalent) TRIAC × 3
TO-220 heatsink × 3
RC snubber per phase (0.1 µF X2 + 100 Ω 1 W) × 3
Gate resistors and signal resistors (assorted 1/4 W)
5 V isolated AC-DC power module (e.g., HLK-PM01)
11.0592 MHz crystal
33 pF crystal capacitors × 2
100 nF decoupling capacitors
10 µF electrolytic capacitor
Tactile push button switches × 2
5 mm indicator LEDs with series resistors
PCB (custom fabricated) and headers
Terminal blocks (5.08 mm) for mains and load connections
ABS project enclosure
 
Features
Zero-cross switching per phase minimizes EMI and inrush, improving reliability on inductive and resistive loads.
Opto-isolated inputs and drivers enhance safety and noise immunity between logic and mains domains.
Independent control for three single-phase channels supports true three-phase sequencing and testing.
CRO/DSO-visible switching edges simplify verification of ZVS timing and triac conduction windows.
Modular BOM with standard 8051 tooling eases firmware development and education use.
 
Applications
Three-phase AC load switching demos for labs and training.
Motor, heater, and lamp banks with reduced switching stress.
Industrial control prototyping where low-noise SSR behavior is required.
Automated test benches for AC load characterization.
 
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)
15cm × 15cm × 10cm (enclosed assembly)
 
Shipping dimensions (cm)
20cm × 18cm × 14cm (boxed with padding)
 
Weight
~0.75 kg (boxed)
 
Estimate project weight
~2 kg (assembled unit without shipping materials)
 
Notes: All the products are made by LearnElectronics India and not for re-sale.