Experiment
3
Binary to GRAY Code Converter, Design of a Two
to Four Decoder (2 to 4) BCD to Seven Segments
Display
Objective
-To implement a Binary to Gray code converter using exclusive-OR gates
References
Donald P.Leach : Experimental in Digital Principles, 3rd Edition
Malvino/Leach : Digital Principles and Applications
Bartee : Digital Computer Fundamentals, 6th Edition
Component
1-74LS04 hex-inverter (NOT) TTL IC
1-74LS08 Quad-two input AND TTL IC
1-74LS47 7 segment Decoder/driver TTL IC
1-74LS86 Exclusive OR TTL IC
1- 7-Segment Display
7-330 Ω Resistor
1- +5V Power supply
1- DC Voltmeter
Introduction
Binary-to Gray Converter
An interesting application for the exclusive-OR gate is a logic gate to
change a binary number to its equivalent in Gray Code. The logic circuit in
fig 2.3 can be used to convert a 4-bit binary number ABCD into its Graycode equivalent, G1,G2,G3 and G4.As an example, the binary number
0011 will be converted into its Gray-Code equivalent of 0010 by the circuit
in fig 3-1. Note : A is the most significant bit and D is the least significant
bit.
Figure 3.1
7-Segment Display
A 7-segment Display is a chip were seven LED’s are constructed and
arranged in the pattern shown in fig-3-2.
Figure 3.2
There are 2 type of 7-Segment Display :
1) Common Anode (C.A): Where all the anodes of the seven LED’s
are connected together.
2) Common Cathode (C.C): Where all the cathodes of the seven
LED’s are connected together.
7- Segment Decoder Driver
The 7-segment decoder driver is a device which can be used to drive a
7-segment LED. There are 2 types of decoder driver corresponding to
the two different 7-segment configurations(C.A;C.C).
Procedure
1) Using the 74LS86 to construct the binary-to-Gray converter shown
in Fig 3-1. Verify the proper operation of the circuit by applying at
least 3 different inputs signals and record the resulting outputs in
the table 1 below.
Table 1
2) Using the same concept design a 5 bit binary-to Gray converter.
Verify the Gray code of the following inputs :
Note : no need to construct circuit experimentally.
a) 11001
b) 01011
3) Design a circuit that will implement the truth table shown in table
2. Explain what the circuit does, where (A,B are inputs) and (Y1,
Y2, Y3, Y4 are outputs) Note : no need to construct circuit
experimentally.
Table 2
4) Set up the circuit shown in fig 3-3. Verify BCD to 7- segment code
conversion by completing the truth table III. Before that find out
the pin configuration of the 7-segment display (i.e diodes
a,b,c,d,e,f and g)
Questions
1. Design the circuit that will convert form Gray to Binary.
2. How do you convert the output states of the decoder circuit in
procedure 2 to active LOW.
3. Verify what is the different between common anode and common
cathode circuit for the 7-segment display
4. Why was a 330 ohm resistor included in the wiring?