Digital Teaching Aid (DED Philippinen, 86 p.)
 (introduction...)
 Preface
 Introduction
 Fundamental Logic Operations - Lesson 1
 Lesson Plan
 (introduction...)
 Introduction
 TTL circuits
 Logic operations
 Handout No. 1
 Worksheet No. 1
 Introduction Boolean Algebra - Lesson 2
 Lesson Plan
 Introduction
 Boolean algebra
 Boolean equations of logic circuits
 NOR and NAN gates
 De Morgan's theorems
 Worksheet No. 2
 Circuit Analysis and Design - Lesson 3
 Lesson Plan
 (introduction...)
 Introduction
 Boolean laws and theorems
 Sum of product method
 Design example
 Handout No. 2
 Worksheet No. 3
 First Evaluation
 Karnaugh Mapping - Lesson 4
 Lesson Plan
 (introduction...)
 Introduction
 Karnaugh map
 Truth table to Karnaugh map
 Overlapping and Rolling
 Worksheet No. 4
 Karnaugh Mapping II - Lesson 5
 Lesson Plan
 (introduction...)
 Introduction
 Product of sums method
 Don't care conditions
 Worksheet No. 5
 Coding - Lesson 6
 Lesson Plan
 (introduction...)
 Introduction
 ASCII code
 Excess-3 code
 Gray code
 Encoder
 Decoder
 Code converter
 Worksheet No. 6
 Flip-Flops - Lesson 7
 Lesson Plan
 (introduction...)
 Introduction
 RS Flip-Flops
 D - Flip-Flop (D-FF)
 JK Flip-Flop (JK-FF)
 Worksheet No. 7
 Second Evaluation
 Counter - Lesson 8
 Lesson Plan
 (introduction...)
 Introduction
 Asynchronous counter
 Synchronous counter
 Seven segment indicator and decoder
 Worksheet No. 8
 Data Processing Circuits - Lesson 9
 Lesson Plan
 (introduction...)
 Introduction
 Multiplexer
 Demultiplexer
 Handout No. 3
 Worksheet No. 9
 Third Evaluation

### Seven segment indicator and decoder

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)

Fig. 8-5: seven LED's labeled a through g

Depending on which LED's are light up it is possible to indicate decimal numbers from 0 to 9.

Fig. 8-6: Seven segment indicator, common anode type

Two types of indicators are available:

- common anode
- common cathode

The diodes are controlled by ground (common anode) or by 5V (common cathode).

Fig. 8-7: Seven segment indicator, common cathode type

Seven segment decoder

Seven segment decocer are devices to drive seven segment indicators.

Ex: The 7448

(see Fig. 8-8 on the next page)

Fig. 8-8: Seven segment indicator and decoder

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.