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7-Segment Displays

These consist of seven LED's arranged so that the numbers 0 to 9 can be displayed by lighting appropriate 'segments'.

The next diagram illustrates how the number 3.57 can be displayed.

The pin arrangement of a typical 7-segment display is shown below.

The seven LED's, (eight if you count the decimal point,) are interconnected in one of two ways, known as common-anode and common-cathode format.

In the common anode format, all the anodes are connected together inside the 7-segment display package. In use, they are then are connected to the positive power supply through a series protective resistor. Normally, the cathodes of all the LED's are held at logic 1. To make a segment light, the cathode of that led is connected to logic 0. This can be done by connecting the display directly to the outputs of a PICmicro chip, or by using a decoder/driver integrated circuit.

In the common cathode format, all the cathodes are connected together internally. In the circuit, they are connected to the negative supply (0V) through a series resistor. Normally, they are held at logic 0, but to light a segment, it is connected to logic 1.