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LED dot matrix driving topologies and panelling
Author(s)
De Villiers, Willem Johannes
Date Issued
2015
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
Different LED dot matrix driving topologies and concurrent data transfer
methods were investigated in this dissertation. The LED dot matrix driving topologies
was first implemented and then tested. The designs tested were: the constant
voltage, constant current, bi-polar and use of an existing LED dot matrix display
driving integrated circuit (IC). All four driving topologies were evaluated to determine
the brightest design. It was found that the constant current design performed the
best, while the existing driving IC did not function at all. The bi-polar was a very close
second while the constant voltage design performed the worst. The improvements in
the bi-polar design with respect to the refresh rate were not enough to warrant the
use of the bi-polar design in future permutations of the hardware. It was decided to
improve the constant current driving topology and use this as the backbone for the
LED dot matrix displays. Since the size of LED dot matrix displays are increasing, a
smarter driving algorithm in conjunction with hardware needed to be developed. It
was therefore decided to subdivide a large LED dot matrix display into smaller
sections called panels. These panels can be connected in a horizontal, vertical, or a
combination of the two to suit the user requirements. The panels were connected to
adjacent panels to aid in determining the display size and configuration. Display
graphics data was then sent to all the panels concurrently even though each panel
still updated serially. This improved the brightness and refresh rate of the entire LED
dot matrix display. Controlling this display required the use of a powerful processor
as the algorithm had to subdivide graphics and distribute these to the panels to be
displayed. Making use of pseudo-addressing, each panel connected to the system
was assigned a temporary address. A Raspberry Pi computer was used to
implement and execute the display algorithm. For connecting the Raspberry Pi
computer to the LED dot matrix display panels, an interface card was developed.
This interface card was only activated once the Raspberry Pi was connected. The
on-board microcontroller on the interface card controlled the LED dot matrix display
brightness. This was done by measuring the ambient light and adjusting the digital
resistors placed on the LED dot matrix panels. The value of these resistors in
conjunction with the current sources used in the hardware design determined the
brightness of the display.
methods were investigated in this dissertation. The LED dot matrix driving topologies
was first implemented and then tested. The designs tested were: the constant
voltage, constant current, bi-polar and use of an existing LED dot matrix display
driving integrated circuit (IC). All four driving topologies were evaluated to determine
the brightest design. It was found that the constant current design performed the
best, while the existing driving IC did not function at all. The bi-polar was a very close
second while the constant voltage design performed the worst. The improvements in
the bi-polar design with respect to the refresh rate were not enough to warrant the
use of the bi-polar design in future permutations of the hardware. It was decided to
improve the constant current driving topology and use this as the backbone for the
LED dot matrix displays. Since the size of LED dot matrix displays are increasing, a
smarter driving algorithm in conjunction with hardware needed to be developed. It
was therefore decided to subdivide a large LED dot matrix display into smaller
sections called panels. These panels can be connected in a horizontal, vertical, or a
combination of the two to suit the user requirements. The panels were connected to
adjacent panels to aid in determining the display size and configuration. Display
graphics data was then sent to all the panels concurrently even though each panel
still updated serially. This improved the brightness and refresh rate of the entire LED
dot matrix display. Controlling this display required the use of a powerful processor
as the algorithm had to subdivide graphics and distribute these to the panels to be
displayed. Making use of pseudo-addressing, each panel connected to the system
was assigned a temporary address. A Raspberry Pi computer was used to
implement and execute the display algorithm. For connecting the Raspberry Pi
computer to the LED dot matrix display panels, an interface card was developed.
This interface card was only activated once the Raspberry Pi was connected. The
on-board microcontroller on the interface card controlled the LED dot matrix display
brightness. This was done by measuring the ambient light and adjusting the digital
resistors placed on the LED dot matrix panels. The value of these resistors in
conjunction with the current sources used in the hardware design determined the
brightness of the display.
Additional information
Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2015
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