PLC Program to Operate Seven Segment Display

This is a PLC Program to Operate Seven Segment Display.

Implement displaying 0-9 digits in 7 Segment LED Display interfacing with PLC using Ladder Diagram programming language.

• 7 Segment LED Displays are also known as BCD to 7 Segment decoder.
• These displays are readily available or can be made easily organizing simple LEDs in the same structure as in actual display.
• Input to this display is BCD number which are decoded into digits 0 to 9.
• Connect this display with Output card of a PLC.
• Write a truth table to energize various outputs according to BCD input applied.
• This displays do not come with internal latches, we can latch inputs in PLC using either seal in contact or Latch-Unlatch instructions in Allen Bradley and Set-Reset instructions in Siemens PLCs.
• Use K-Map to obtain output equations.
• Implement this equations in Ladder Diagram format using AND and OR operations.

Truth Table of 7 Segment Display

Inputs	Outputs
	a b c d	e f g	Display
0000	1 1 1 1	1 1 0	0
0001	0 1 1 0	0 0 0	1
0010	1 1 0 1	1 0 1	2
0011	1 1 1 1	0 0 1	3
0100	0 1 1 0	0 1 1	4
0101	1 0 1 1	0 1 1	5
0110	1 0 1 1	1 1 1	6
0111	1 1 1 0	0 0 0	7
1000	1 1 1 1	1 1 1	8
1001	1 1 1 1	0 1 1	9

Simplified Boolean expressions to obtain a to g outputs using K-Map

Here is PLC program to Operate Seven Segment Display, along with program explanation and run time test cases.

List of Inputs and Outputs
I:1/0 to I:1/3	= I0 Input 0 to I3 Input 3 respectively.	(Input)
O:2/0 to O:2/6	= a to g respectively.				(Outputs)

Ladder Diagram for 7 segment display

• After performing K-Map simplification method, equations for all the 7 outputs are obtained.
• I:1/0 to I:1/3 are the inputs I0 to I3 respectively and O:2/0 to O:2/6 are the outputs ‘a’ to ‘g’ respectively.
• Output ‘a’ 0:2/0 energizes in 4 cases, when I2 and I0 are low, I1 is high, I0 and I2 are high or when I3 is high.
• Output ‘c’ O:2/2 energizes in 3 cases, when I1 is low, I0 is high, or when I2 is high.
• Similarly all the remaining outputs b, d, e, f and g are obtained.
• Simply this is a method to convert BCD inputs into Seven Segments to display 0-9 digits.

Separated by commas are different cases of outputs being energized.

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