The BCD or Binary Coded Decimal (BCD) decoder is a device that converts a digital format of a value into a format that displays devices such as the 7-segment display can interpret into a human-readable For instance, we need to use a BCD to 7-segment decoder in order to display a four-bit binary number from 0000 (0 in base 10) to 1001 (9 in base 10 ) on a 7-segment display In digital electronics, numbers are generally represented by their binary values.What is a BCD decoder and why do we need it to display a number?.As this device is made out of LEDs, it requires resistors order to limit the current supply.