An approach towards greening the digital display system

An Approach Towards Greening the Digital Display
System
Alvi Md.Ishmam
Department of Computer Science and Engineering
Bangladesh University of Engineering and Technology, Dhaka, Bangladesh
1305092.am@ugrad.cse.buet.ac.bd
December 20, 2017
Alvi Md.Ishmam (BUET) Green Display December 20, 2017 1 / 25

Overview
1 Background and Motivation
2 Our Proposed Methodology
Research Context
3 User Evaluation
4 Future Work

Background of Our Study
Figure: Digital signage display

Background of Our Study
Versatile application such as displaying information on electrical
equipment, advertisement on billboard.
About 70% of American people who notice a digital video display,
among 47% of them can speciﬁcally recall them
14inch * 48inch LED billboard(10000 diode) consumes 162,902 KWh
per year

Motivation Behind Our Study
The power hungriness of a LED display system such as dot matrix
display is higher than any other components of an electronic device
[dotmatrix]

[dotmatrix]
Pulse width modulation (PWM) operation, i.e., varying the duty cycle
is selected as the best dimming strategy
[Rodrigues,Morais, Garcia,Dalla-Costa]

[dotmatrix]
Pulse width modulation (PWM) operation, i.e., varying the duty cycle
is selected as the best dimming strategy
[Rodrigues,Morais, Garcia,Dalla-Costa]
Varying the duty cycle on dot matrix display and ﬁnding the optimal
operating point is yet to be addressed.

Related Research Work
[Koh,Wang]
A low voltage DC (LVDC) grid powered LED lighting system was proposed
here. About 44.2% energy saving is possible in this proposed system which
is a perfect dominance over AC ﬂuorescent system.

Related Research Work
Focuses on only power consumption reduction ignoring brightness,
visibility etc.
No trade-oﬀ between brightness and power consumption reduction
An optimal operating point is yet to be proposed

Our Research Context
Reducing the power consumption of LED dot matrix based signage display
by exploiting the three fundamental parameters.
Duty Cycle

Duty Cycle
Frame Rate

Duty Cycle
Frame Rate
System Frequency

Can We Experiment with a Large Signage Display?

Solution
Figure: 8*8 dot Matrix Display

Overview of Experimental Procedure
Figure: Block Diagram

The Instrumentation
2*4 dot matrix display

The Instrumentation
8 display arranged in 2 row

The Instrumentation
Shift registers & Darlington transistor arrays

The Instrumentation
Shift registers & Darlington transistor arrays
Power consumption reduction

The Instrumentation
Figure: Setup of Experiment

Unveiling the Parameters
Duty Cycle: At which proportion system is operational
Pavg = Ppeak × dutycycle (1)

Duty Cycle: At which proportion system is operational
Pavg = Ppeak × dutycycle (1)
By pausing the row selection for small amount of time (95% duty
cycle) brightness does not reduce signiﬁcantly.

Frame Rate: Determines how fast LED’s are illuminated

Cannot animate all LED’s at once

Animate one by one within 0.1 second to deceive human eye.

Animate one by one within 0.1 second to deceive human eye.
Reduced frame time or high frame rate reduces power consumption

System Frequency Frequency of micro-controller( Atmega32)

Two system frequency (16MHz, 8MHz)

Two system frequency (16MHz, 8MHz)
Reduced frequency leads to reduced power consumption

Experimentations and Findings
Luminous Eﬃcacy
Luminous eﬃcacy(per unit area) = Illuminance / Power consumption
A portion of Calculation Table:

Figure: Duty cycle versus luminous eﬃcacy per unit area at 16 MHz system
frequency

Figure: Duty cycle versus luminous eﬃcacy per unit area at 8 MHz system
frequency

Summary of ﬁndings
The minimum frame rate to avoid ﬂickering are 50% and 100% for
16MHz and 8MHz system frequency.

The maximum eﬃcacy is at 85% and 60% duty cycle at 16MHZ and
8MHz frequency.

The maximum eﬃcacy is at 85% and 60% duty cycle at 16MHZ and
8MHz frequency.
Power reduction at those points are 14.54% and 40% and brightness
decreased about 12.5% and 37.5%

User Evaluation and Optimality
User selection criteria:
Wear no spectacles
Both male and Female
Optimality
The optimal operating point is 85% duty cycle, 50Hz frame rate and
16MHz system frequency.

Future Work
Color blind people
People with eyesight problem
All other dot matrix display

References
Dot Matrix Display datasheet. https://goo.gl/RpGnLj.
Rodrigues, W.A., Morais, L.M.F., Donoso-Garcia, P.F., Cortizo, P.C. and Seleme,
S.I., 2011, September. Comparative analysis of power LEDs dimming methods. In
XI Brazilian Power Electronics Conference (pp. 378-383). IEEE.
Garcia, J., Dalla-Costa, M.A., Cardesin, J., Alonso, J.M. and Rico-Secades, M.,
2009. Dimming of high-brightness LEDs by means of luminous ﬂux thermal
estimation. IEEE transactions on Power Electronics, 24(4), pp.1107-1114.
L. H. Koh, Y. K. Tan, Z. Z. Wang and K. J. Tseng, An energy-efcient low voltage
DC grid powered smart LED lighting system, IECON 2011 - 37th Annual
Conference of the IEEE Industrial Electronics Society, Melbourne, VIC, 2011, pp.
2883-2888.

Thank You
Questions Are Welcome!!

An approach towards greening the digital display system

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