Project idea
A zero‑cross detected, microcontroller‑timed firing system adjusts a triac/thyristor bridge to deliver controlled DC for battery charging using an 8051 family MCU.
An opto‑triac driver provides isolated gate triggering from the 8051 while a regulated 5 V rail and crystal clock ensure stable timing.
 
Project description
AC mains is stepped down, zero‑cross is sensed by a comparator stage, and timing delays are computed by the AT89S52 to fire the triac via an MOC3021 for phase‑angle control feeding a bridge rectifier.
The rectified DC is measured across a resistive load (battery surrogate) while push buttons let the user increase or decrease conduction angle to set charging voltage/current.
 
Total list of components
AT89S52 8051 MCU with 40‑pin DIP socket,
11.0592 MHz crystal,
2×22 pF capacitors, reset RC network
Opto‑triac driver MOC3021 with gate resistor network
Triac BT136‑600 series with snubber (RC) and heat sink as needed
LM358 dual op‑amp for zero‑cross/comparator stage
7805 linear regulator with input diode and electrolytic/ceramic decoupling
Step‑down transformer 12‑0‑12 V, 1 A
Bridge rectifier (discrete or module), filter electrolytics, bleeder resistor
Tactile push buttons (UP/DOWN/SET), LEDs for status
General purpose PCB 14×9 cm or custom PCB,
headers, wires, terminals
Misc passives: resistors, capacitors, snubber RC, gate resistors, opto LED limits, etc.
 
Features
Isolated firing using an opto‑triac driver improves safety and noise immunity during phase control.
Microcontroller‑set firing angle enables precise DC output adjustment for charging profiles.
Push‑button UI with status indication for quick voltage/current tuning during tests.
 
Applications
Bench‑top lead‑acid or SLA charger control prototype using phase‑controlled rectification.
Educational demo of zero‑cross detection, firing delays, and thyristor/triac control with an 8051.
 
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 in protective foam box approximately 20×15×10 cm to accommodate the 14×9 cm PCB and transformer.
Includes cable and printed quick‑start sheet within the same parcel.
 
Weight
Assembled electronics excluding transformer: roughly 120–180 g based on PCB, passives, and DIP MCU.
Transformer contributes the majority of mass in the kit.
 
Estimated project weight: 1kg
 
Notes: All the products are made by LearnElectronics India and not for re-sale.