Output Circuit

 1. LCD

LCD pins diagram

The most commonly used LCDs found in the market today are 1 Line, 2 Line or 4 Line LCDs which have only 1 controller and support at most of 80 characters. Most LCDs with 1 controller has 14 pins. Pin description is shown in the table below:

Character LCD pins with 1 controller

Display data RAM (DDRAM) stores display data represented in 8-bit character codes. Its extended capacity is 80 X 8 bits, or 80 characters. The area in display data RAM (DDRAM) that is not used for display can be used as general data RAM. So whatever user sends on the DDRAM is actually displayed on the LCD. For LCDs like 1x16, only 16 characters are visible, so whatever user write after 16 chars is written in DDRAM but is not visible to the user.

LED circuit connection

Above is the connection diagram of LCD in 4-bit mode, only 7 pins needed to interface with an LCD. D4 - D7 are the data pins connection and Enable and Register select are for LCD control pins. The Read/Write (RW) pin of the LCD will not be using, as the data only writing on the LCD. So, it has to be grounded permanently. If user wants to use it, then they may connect it on controller but that will only increase another pin and does not make any big difference. The unwanted data pins of LCD i.e. Vss, VEE and D0-D3 are connected to ground.

There are many reasons why use LCD in 4-bit mode instead of 8-bit. One basic reason is lesser number of pins are needed to interface LCD.

2. LED

LED Output Circuit

When OUTPUT 2 receive logic condition from the microcontroller, R10 (330kohm) will limit the current to the D3 LED. The D3 LED will on.

3. Relay Switching

Relay Switching Circuit

For the above circuit, when the base of the transistor receive any supply from the microcontroller, it will allow the 5V to the ground without active the relay. Otherwise, the relay will active and create a back e.m.f that will turn the switching from the normally open to normally close (which is turn on the Backup RCCB).