Four Digit Seven Segment Display

In this lesson, you will learn how to use a 4-digit 7-segment display.

When using a 1-digit 7-segment display, please notice that if it is a common anode, the common anode pin connects to the power source; if it is a common cathode, the common cathode pin connects to the GND.

When using a 4-digit 7-segment display, the common anode or common cathode pin is used to control which digit is displayed. Even though there is only one digit working, the principle of Persistence of Vision enables you to see all numbers displayed because each the scanning speed is so fast that you can hardly notice the intervals.

LCD1602 Display

LCD1602 module is a display that has an LED backlight and can display two rows with up to 16 characters on each row. You can see the rectangles for each character on the display and the pixels that make up each character. The display is just white on blue and is intended for showing text.

Lining up the display with the top of the breadboard helps to identify its pins without too much counting, especially if the breadboard has its rows numbered with row 1 as the top row of the board. Do not forget, the long yellow lead that links the slider of the pot to pin 3 of the display. The 'pot' is used to control the contrast of the display.

74HC595 and LEDs

74HC595 is a Serial to Parallel Converter which has eight outputs (perfect) and three inputs that you use to feed data into it a bit at a time.

This chip makes it a little slower to drive the LEDs (you can only change the LEDs about 500,000 times a second instead of 8,000,000 a second) but it's still really fast, way faster than humans can detect, so it's worth it!

74HC595 shift register is a type of chip that holds what can be thought of as eight memory locations, each of which can either be a 1 or a 0. To set each of these values on or off, we feed in the data using the 'Data' and 'Clock' pins of the chip.

DC Motors and the Fan

In this lesson, you will learn how to control a small DC motor using a MEGA 2560 and a transistor.

The small DC motor is likely to use more power than a MEGA 2560 board digital output can handle directly. If we tried to connect the motor straight to a MEGA 2560 board pin, there is a good chance that it could damage the MEGA 2560 board. A small transistor like the PN2222 can be used as a switch that uses just a little current from the MEGA 2560 board digital output to control the much bigger current of the motor.