Display Module
7-Segment Display
From the Block Diagram shown in the Project Description page, the resultant vector of a magnetic flux density will be show on the Display Module
This display module in particular, will use 4 unit of 7-segment displays as the output platform.
This module is to be designed, layed out and fabricated on PCB with compatible output port from the Axman microcontroller
This display module in particular, will use 4 unit of 7-segment displays as the output platform.
This module is to be designed, layed out and fabricated on PCB with compatible output port from the Axman microcontroller
Basics
Each 7-segment display is a group of 7 LED segments, combined in such way so it can display alphanumerical data, from 0-9 as well as A, b, c, d, E, F.
Figure 1 Figure 2
Figure 1 from above shows numerical display from 0 - 9, and from figure 2, we can see the letter A-F can be shown by turning on segments C,D,E,F and G and so on.
Logics
Since, there are 16 entries (0-9, A-F), they can be represented by 4 bits combinational logic. Because the display unit have a common anode, a low voltage signal is requires at the cathode pins in order to light up the respective segment.
To do this, I generated Product of Sum (POS) for each segment and produced a corresponding truth table
To do this, I generated Product of Sum (POS) for each segment and produced a corresponding truth table
- A = Prod_of_Sum - (0,2,3,4,5,6,7,8,9,A,E,F)
- B = Prod_of_Sum - (0,1,2,3,4,7,8,9,A,d)
- C = Prod_of_Sum - (0,1,3,4,5,6,7,8,9,A,b,d)
- D = Prod_of_Sum - (0,2,3,5,6,8,b,c,d,E)
- E = Prod_of_Sum - (0,2,6,8,9,A,b,E,F)
- F = Prod_of_Sum - (0,4,5,6,8,9,A,b,E,F)
- G = Prod_of_Sum - (2,3,4,5,6,8,9,A,b,c,d,E,F)
GAL16V8
This combinational logic is then burnt onto the GAL16V8, a electrically erasable programmable logic device (PLD), using WinCUPL for logic definition and Needham's Electronics EMP11 for the actual programming of the chip.
Wiring
The resistor value of the between the GAL and the display is determined by:
Since 125 ohm resistor is not a standard resistor value (the closest standard values are the 100 ohm on the lower end and the 220 ohm on the higher end), 220 ohms resistors are used to prolong the life span of the 7 segment display as oppose to the 100 ohm resistors.