|Digital Teaching Aid|
|Counter - Lesson 8|
Seven segment indicators
Seven segment indicators are made by seven LED's. LED's are light emitting diodes. (LED function: Free electrons recombine with holes near the junction. As the free electrons fall from a higher energy level to lower one, they give up energy in form of heat and light)
Depending on which LED's are light up it is possible to indicate decimal numbers from 0 to 9.
Two types of indicators are available:
- common anode
- common cathode
The diodes are controlled by ground (common anode) or by 5V (common cathode).
Seven segment decoder
Seven segment decocer are devices to drive seven segment indicators.
Ex: The 7448
(see Fig. 8-8 on the next page)
The 7448 is a decoder to drive common cathode indicators.
When the BCD input is set to:
A B C D = 0 1 0 0
The internal logic of the decoder forces the LED's b, c, f, and g to conduct.