Microcontrolling an LCD & LED

Ever wondered how a display system works? Right from the traffic lights seen on busy roads, to the laptop or mobile display on which you are currently reading this blog, the tech involved may seem daunting at the surface, but its logic is relatively simple.

In fact, the simplicity might appeal to your curiosity, setting you on the path towards your very first electronics project, just like me. Well then, let’s dive in!

LCDs and LEDs – what are they?

Note: The LCD discussed here is a screen that displays characters, while the LED I have used is a simple diode, with two terminals. It’s different from LED displays, which is another category of flat-panel screens.

LCD is short for Liquid Crystal Display, and is most commonly seen in handheld calculators. It basically consists of a layer of liquid crystal sandwiched between two polarizing sheets. These sheets must be oriented at right angles to each other, otherwise the display won’t work. Its lowermost layer is either a mirror or an LED panel (if it’s backlit). To avoid confusion, I shall only discuss reflective layer LCDs here.

These displays are divided into cells, whose liquid crystal is individually controlled. In the OFF state, the liquid crystal is in a helical configuration, allowing light entering the top polarizer to pass through the second polarizer as well, resulting in a blank screen. Once it enters the ON state, the liquid begins to ‘untwist’, causing light to get blocked by the second polarizer, making the cell appear black in colour.

On the other hand, the LED (or Light Emitting Diode) is a two terminal device that is relatively easy to use, and may be plugged into a circuit, just like any other component. Being the latest advancement in indoor lighting solutions, it significantly improves over incandescent and fluorescent technologies, being more energy efficient than them.

Though this project uses both an LCD and an LED, I have laid more emphasis on the former’s functioning, as it requires more inputs for setting the cursor position, and ensuring that the output text is displayed in the way intended. The LED is simply a blinking bulb in this project.

Enter Arduino – the microcontroller

The Arduino project can be traced back to 2003, with Masimmo Benzi, along with fellow students at the Interaction Design Institute Ivrea, attempting to create a range of microcontrollers that is economical for students and professionals. Today, it is a leading manufacturer of open source hardware, and has a wide consumer base.

From what I read, it’s useful in creating a large number of projects, which I shall put to test, starting with this project. Here, I have used an Arduino Uno to control the LCD screen and LED bulb’s behaviour.

Assembling the hardware

The main components used in this project are: an LED(3V), a 220 Ω resistor, a 16×2 LCD character display (Hitachi HD44780), a solderless breadboard, a 10 KΩ potentiometer(for brightness control), an Arduino Uno, and an A/B USB 2.0 cable (for connecting the Arduino board to the computer).

A few optional but useful tools include: a table lamp, a wire cutter, a penknife, and a pair of tweezers (to pull out wire stubs in case a wire snaps).

Here’s the circuit’s breadboard view:

The data inputs of the LCD screen are assigned values from D0 to D7. In this project, I have used the 4-bit mode of operation, since only 4 data lines have been used.

It is recommended that the wires to the character display be soldered, as it avoids unnecessary data loss at its input pins.

Getting the code right

You may obtain the program code via this link to my GitHub repository:

https://github.com/the-visualizer/lcd_led/blob/master/program-1.ino

The Arduino IDE is required to compile the program, and upload it to the microcontroller board. Here is the link to its download page:

https://www.arduino.cc/en/Main/Software

Fire up the sytem!

Finally, the A/B cable is connected to the computer’s USB port. Once the Arduino board has been correctly identified, along with its COM port, the program is uploaded, and the result obtained is something like this:

Notice that the Arduino board’s built-in LED (the dot next to the red LED bulb) flashes at the same frequency as the latter.

The potentiometer’s knob will require some toggling in order to get the correct brightness for the LCD screen.

Change the arguments of delay(), print() and setCursor(), and see how it alters the output. Is it expected, unusual, or dramatic?

Further, if I want a scrollable display, what hardware/software modifications do I need? Leave your suggestions in the comment section!

Related Links

Fundamentals of Liquid Crystal Display; a white paper:

http://www.fujitsu.com/downloads/MICRO/fma/pdf/LCD_Backgrounder.pdf

The History of the Light Bulb; an article:

https://energy.gov/articles/history-light-bulb

LED Basics; a video:

https://www.youtube.com/watch?v=Yo6JI_bzUzo

Arduino – Troubleshooting:

https://www.arduino.cc/en/guide/troubleshooting

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