A Seven Segment Display or SSD in short is a cool electronic device that shows numbers in a way we can see easily.
It is made up of seven tiny light emitting diodes LEDs that are arranged to look like the number ‘8’.
This setup allows the display to show numbers from 0 to 9 and a few letters too.
You can find these displays in lots of gadgets like digital clocks, calculators and various electronic tools.
There are two main types of SSDs based on how they are set up:
- Common Cathode (CC) Seven Segment Display
- Common Anode (CA) Seven Segment Display
Understanding the differences between these two types is really important if you want to connect them correctly to microcontrollers, Arduino boards and other electronic circuits.
Below we will go through the pinouts, datasheets, workings, constructions, formulas for better understanding of seven segment display.
Diagram with Pinouts:
Pin Configuration:
A Seven Segment Display usually has 10 pins which includes one common pin.
Below table is how they are set up:
| Pin | Segment | Function |
|---|---|---|
| 1 | E | Controls segment ‘E’ |
| 2 | D | Controls segment ‘D’ |
| 3 | Common | Common Cathode/Anode |
| 4 | C | Controls segment ‘C’ |
| 5 | DP | Controls the decimal point (optional) |
| 6 | B | Controls segment ‘B’ |
| 7 | A | Controls segment ‘A’ |
| 8 | Common | Common Cathode/Anode |
| 9 | F | Controls segment ‘F’ |
| 10 | G | Controls segment ‘G’ |
The Common pin is either connected to ground (Common Cathode) or to a positive voltage (Common Anode).
Common Cathode (CC) vs Common Anode (CA)
Common Cathode (CC):
In a Common Cathode SSD all the cathodes of the LED parts are linked together and connected to the ground.
To turn on a segment, you have to connect the right anode to a HIGH signal.
This setup is used in circuits where a logic HIGH (1) is needed to activate a segment.
Common Anode (CA):
In a Common Anode SSD all the positive sides (anodes) of the LED segments are linked to a positive voltage source (+Vcc).
To turn on a segment, you have to connect the right negative side cathode to a LOW signal.
This setup is used in circuits where a LOW signal (0) is needed to light up a segment.
Difference Table:
| Feature | Common Cathode | Common Anode |
| Common Pin Connection | Ground (0V) | +Vcc (5V, 12V, etc.) |
| Logic for Segment ON | HIGH (1) | LOW (0) |
| Preferred in | Microcontroller-based projects | Digital Circuits |
Datasheet Overview:
A regular datasheet for a seven segment display usually includes:
Forward Voltage: Ranges from 1.8V to 2.2V for each LED part
Current Usage: Between 10mA and 20mA for each segment
Power Loss: Varies based on how many segments are lit up
Viewing Angle: Generally about 30° to 60°.
Working Principle:
Each part of the display has an LED, and by turning on certain combinations of these LEDs, we can create the number we want to show.
For instance, to show the number 8 all seven segments (labeled A to G) need to be lit up.
Example: Displaying Numbers on a Common Cathode SSD
Decimal Digit Representation (CC)
| Digit | A | B | C | D | E | F | G |
| 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 |
| 1 | 0 | 1 | 1 | 0 | 0 | 0 | 0 |
| 2 | 1 | 1 | 0 | 1 | 1 | 0 | 1 |
| 3 | 1 | 1 | 1 | 1 | 0 | 0 | 1 |
| 4 | 0 | 1 | 1 | 0 | 0 | 1 | 1 |
| 5 | 1 | 0 | 1 | 1 | 0 | 1 | 1 |
| 6 | 1 | 0 | 1 | 1 | 1 | 1 | 1 |
| 7 | 1 | 1 | 1 | 0 | 0 | 0 | 0 |
| 8 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 9 | 1 | 1 | 1 | 1 | 0 | 1 | 1 |
For Common Anode the logic is inverted (0 turns a segment ON).
Construction:
The SSD is usually made up of:
Outer Material: Often plastic or a type of resin called epoxy.
LED Parts: Seven separate LEDs that are set up in a shape like the number 8.
Wiring Inside: The LEDs are connected using either a common anode or cathode setup.
Metal Pins: These are the metal parts on the outside that connect to other circuits.
Formulas and Calculations:
To make sure everything works safely, you need to use the right resistors in a line with each part.
You can figure out the resistor value by using ohms Law.
Resistor Calculation:
where:
- Supply voltage (e.g 5V or 12V)
- Forward voltage drop of LED (~2V)
- Desired current (~10mA to 20mA)
For example with a 5V supply and 2V LED forward voltage:
R = 5V – 2V / 10mA = 300Ω
A 330Ω resistor is commonly used.
Conclusion:
Seven Segment Displays are important parts used in many numerical displays for different purposes.
Knowing how they work, the different types (like Common Cathode and Common Anode) and how to connect them helps in making better circuit designs.
Even though newer technologies like OLED and LCD are popular, SSDs are still a dependable and budget friendly option for basic number displays.
With the right resistor values and logic levels they can easily be used in projects with microcontrollers, such as Arduino and Raspberry Pi.
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