Thus at 6mA current we would require a series current limiting resistor of 533Ω, or 560Ω to the nearest preferred value, and to limit the current to 20mA we would require a resistor of 160Ω. Thus a 7-segment display can be either a Common Cathode (CC) or a Common Anode (CA) type display. Likewise, when all the anode terminals of the LEDs used in the display are shorted together, the display is referred to as a Common-anode, (CA) display. When the cathode terminals of all the LEDs used in the display are shorted together, the display is referred to as a Common-cathode, (CC) display. Thus instead of having 14 connecting pins for the display we will only have only eight (7 + 1) pins, one each for the seven individual LEDs plus a common pin, and it is this “common pin” which identifies the type and name of 7-segment display. While an LED segment can be illuminated individually as required, one terminal of each internal LED is connected to a common point or node. So if a 7-segment display consists of seven LED’s (ignoring the decimal point for now), one for each segment, and an LED has two terminals, an Anode and a Cathode, does that mean that each single 7-segment display will have 14 connecting pins or terminals.
This difference between the two is that an LED emits light energy from its PN-junction when an electrical current passes through it. So how can we do this.ħ-segment displays provide a convenient way of displaying numerical information from zero to nine as they basically consist of a load of light emitting diodes connected together within a single indicator package.Įach light emitting diode (called a segment) is illuminated using an electrical current, and by illuminating various combinations of segments so that some segments will be turned “ON” and emitting light while others will be turned “OFF” we can display individual characters or numbers.Īs we saw in our tutorial about the Light Emitting Diode, LEDs are just like normal diodes, in that they only allow current to flow in one direction. But sometimes as an Electronics student or hobbyist we want to display two or more numbers or digits as part of our project or digital logic circuit. Nowadays it is very easy to display numbers and letters across multiple LED displays using micro-controllers, such as the Arduino or Raspberry-Pi, along with a small bit of software related code to display the required digits.
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