The following project demonstrates a basic application of 89S52 micro-controller to manage different output loads and protecting the access of these loads with the help of an embedded password, in short: a Password Circuit Breaker.

Step 1: Components Required

89S52 development board
16x2 LCD Module
4 channel relay module
4x4 Matrix Keypad
Potentiometer
Jumper wires
Conducting Wires
12V Battery (power supply)
Wooden frame
Polystyrene sheet

Now if you prefer the load to be a DC output then you need the following components:

4 LEDS (keep extras for testing)
330 ohm resistors

Or else if you prefer an ac source at the load terminal then you will need:

4 ac bulbs (along with sockets)
Adapter

Note: If you desire to make your project a little more geeky, you can make your own adapter with the help of a transformer and a rectifier. Google it.

Step 2: Mind Map || Flow Diagram

Our mind map provides a generalized ideation of the topic's different aspects such as its key problems and solutions, the props required etc.

The flow diagram shows step-by-step information as to how the complete system will move forward.

Step 3: Electrical Circuit Diagram

In our project we made use of dc supply to activate the load. You can use an ac input too!

Step 4: Pin Configuration

Here is how the pin configuration has been setup into the programmable board with different components.

P1.0 - P1.7 = Keypad Matrix

P3.1 - P3.4 = Relay Input (IN1, IN2, IN3, IN4) [ VCC and GND pins to 5V and GND pin of board]

P2.4 - P2.7 = LCD data line input

P0.4 - P0.5 = RS and Read/Write port of LCD

Note: Here we have made 4-bit data transmission into the lcd to make the coding easier.

Step 5: Relay Wiring

Make sure all the common terminals are connected together. COM port will be connected to 5V pin of development board.

Next all the NO terminals will be given to respective loads (in our case LEDs).

NOTE: It is to be made sure that the maximum current through the leds should not exceed 15mA.

So here with supply of 5V and current of 15mA we know V=I*R.

Therefore we require resistance R=330 (ohms)

Step 6: Final Setup

Once the complete wiring is completed, next step is proper placement of the setup

Here we designed a wooden frame such a sheet of polystyrene could be fix just below it.

Next, cover the top of the frame with white sheet of chart-paper for proper presentation.

At last fix all the components over the top using pins that will pierce through the polystyrene.