Sep 012014
 

Seven Segments Display, 7-segment Display

The 7-segment display, is a component that is used to represent numbers in many electronic devices.

Today, it is very common to find LCDs in many electronic equipments (due to its very low energy demand), but there are many that still use the 7-segment display for its simplicity. This element is made in a way that we can activate each segment (LED) separately, and by combining these segments we can represent all the numbers on the display (from 0 to 9).

The most common 7-segment display color is red, due to its easy visualization. A letter is assigned to each segment of the display. This letter identifies its position on the display. Look at the picture.

7-segment display - Seven segment display

  • If all segments are activated (on), they will form the number “8”
  • If only segments “a, b, c, d, f,” are activated, they will form the number “0”
  • If only segments “a, b, g, e, d,” are activated, they will form the number “2”
  • If only segments “b, c, f, g,” are activated, they will form the number “4”

d.p.: represents the decimal point

The common anode 7-segment display

In the common anode 7-segment display, all LEDs anodes are joined and connected to the power supply. To activate any segment we must connect the cathode of these segment to ground. (Low voltaje).

Each segment conection has a current limiting resistor. This resistor controls (limits) the segment current to a safe value.
Common anode 7-segment display

The common cathode 7-segment display

In the common cathode 7-segment display, all LEDs cathodes are joined and connected to ground. To activate a segment we must connect the anode of this segment to Vcc (DC power supply).

Each segment conection has a current limiting resistor. This resistor controls (limits) the segment current to a safe value.
Common cathode 7-segment display
Each segment needs at least 2 volts, and a current of 5 mA to operate properly. If we have a 5 volts DC supply (Vcc = 5 volts), the resistor value will be: R = (Vcc–2 volts)/5 mA = 600 ohms. (A 680 ohms resistor will work fine.)

Note: There are alphanumeric displays that allow the representation of letters and numbers.

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