JunMultiLED - Revision history

imported>Student2018: /* Appendix */

2018-12-15T04:51:39Z

Appendix

← Older revision		Revision as of 04:51, 15 December 2018
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	==Appendix==		==Appendix==

	The project was focused on designing a lighting system capable of uniform output. In the process however, it was found that a simple smoothing filter would be able to correct for non-uniform input. A Savitsky-Golay filter with a window length of 51 elements and 3rd-order polynomial smoothed the raw BGR value to the point where the peak-to-peak value of the gradient of the BGR value was significantly reduced.		The project was focused on designing a lighting system capable of uniform output. In the process however, it was found that a simple smoothing filter would be able to correct for non-uniform input. A Savitsky-Golay filter with a window length of 51 elements and 3rd-order polynomial smoothed the raw BGR value to the point where the peak-to-peak value of the gradient of the BGR value was significantly reduced. This was done after the application of an RFFT found that distortion could not be isolated to specific frequencies.

	[[File:SavitskyGolay.png\|800px\|thumb\|center\|'''Figure 17:''' Sample BGR Figure converted to BGR plot]]		[[File:SavitskyGolay.png\|800px\|thumb\|center\|'''Figure 17:''' Sample BGR Figure converted to BGR plot]]

imported>Student2018: /* Introduction */

2018-12-15T04:50:11Z

Introduction

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	==Introduction==		==Introduction==

	Multispectral imaging has enabled identification and analysis of targets across sectors, from agriculture to defense. This project focuses on the practical engineering-related aspects of creating an illumination system for future use in a portable multispectral imager. Specifically, this work describes efforts to characterize and evaluate the non-uniformity of high-power LEDs for this illumination system, as well as efforts to mitigate the associated challenges from running such a system. Non-uniformity of output light must be controlled to minimize any artifacts or distortions that the illuminations system itself introduces. Below shows an example of how a commercially-available multispectral imager (the Forenscope) can be used to visualize anomalies in dental tissue.		Multispectral imaging has enabled identification and analysis of targets across sectors, from agriculture to defense. This project focuses on the practical engineering-related aspects of creating an illumination system for future use in a portable multispectral imager. Specifically, this work describes efforts to characterize and evaluate the non-uniformity of high-power LEDs for this illumination system, as well as efforts to mitigate the associated challenges from running such a system. Non-uniformity of output light must be controlled to minimize any artifacts or distortions that the illuminations system itself introduces. Below shows an example of how a commercially-available multispectral imager (the Forenscope) can be used to visualize anomalies in dental tissue, an example of point-of-contact medical scenarios where such a portable imager may be helpful.

	[[File:ForenscopeImages.png\|800px\|thumb\|center\|'''Figure 1:''' Multispectral Images of Teeth [1]]]		[[File:ForenscopeImages.png\|800px\|thumb\|center\|'''Figure 1:''' Multispectral Images of Teeth [1]]]

imported>Student2018: /* Camera */

2018-12-15T04:49:19Z

Camera

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	The Point Grey Flea3 USB camera was used to capture images.		The Point Grey Flea3 USB camera was used to capture images.

	[[File:Flea3.jpg\|600px\|thumb\|center\|'''Figure 8:''' Point Grey Flea3 [5]]]		[[File:Flea3.jpg\|600px\|thumb\|center\|'''Figure 8:''' Point Grey Flea3 [6]]]

	Two separate configurations were used:		Two separate configurations were used:

imported>Student2018: /* LED Driver */

2018-12-15T04:48:59Z

LED Driver

← Older revision		Revision as of 04:48, 15 December 2018
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	A DC-DC step-down converter, alternatively known as a buck converter, was used to limit and control the current supplied to the LED. Although many options were available, the AL8805 was ultimately selected. Its 6V to 36V input was within the 12V range of the lab’s power supply, eliminating the need to purchase additional test equipment. The control voltages for the IC were 2.6V to 5.5V, meaning most micro controllers could directly interface with the IC. Most importantly though, the AL8805 could tolerate up to 1A of continued switch current but could be set to a lower output current based on the feedback resistors interfaced to it. The IC was set to output approximately 350mA of current, lowering the total dissipated heat. The IC and supplementary passives were available as a PCB from Sparkfun; the board’s schematic and picture follow below:		A DC-DC step-down converter, alternatively known as a buck converter, was used to limit and control the current supplied to the LED. Although many options were available, the AL8805 was ultimately selected. Its 6V to 36V input was within the 12V range of the lab’s power supply, eliminating the need to purchase additional test equipment. The control voltages for the IC were 2.6V to 5.5V, meaning most micro controllers could directly interface with the IC. Most importantly though, the AL8805 could tolerate up to 1A of continued switch current but could be set to a lower output current based on the feedback resistors interfaced to it. The IC was set to output approximately 350mA of current, lowering the total dissipated heat. The IC and supplementary passives were available as a PCB from Sparkfun; the board’s schematic and picture follow below:

	[[File:LEDDriverCircuit.png\|600px\|thumb\|center\|'''Figure 6:''' Converter schematic[4]]]		[[File:LEDDriverCircuit.png\|600px\|thumb\|center\|'''Figure 6:''' Converter schematic [5]]]

	[[File:BuckBoard.jpg\|600px\|thumb\|center\|'''Figure 7:''' Converter picture[4]]]		[[File:BuckBoard.jpg\|600px\|thumb\|center\|'''Figure 7:''' Converter picture [5]]]

	===Camera===		===Camera===

imported>Student2018: /* Experimental Setup */

2018-12-15T04:48:40Z

Experimental Setup

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	iPixel LED’s 3W “warm white” (3000-3300nm) power LEDs packaged on an aluminum-backed PCB base were chosen for their availability and ease of use. According to the provided datasheet, each LED had an expected forward current of 750 mA with an absolute maximum of peak pulsed forward current of 3A. In addition, the worst-case forward voltage drop across the LED is 3.8V while the minimum voltage drop is 3.2V.		iPixel LED’s 3W “warm white” (3000-3300nm) power LEDs packaged on an aluminum-backed PCB base were chosen for their availability and ease of use. According to the provided datasheet, each LED had an expected forward current of 750 mA with an absolute maximum of peak pulsed forward current of 3A. In addition, the worst-case forward voltage drop across the LED is 3.8V while the minimum voltage drop is 3.2V.

	[[File:PowerLEDPicturewithCoin.jpg\|500px\|thumb\|center\|'''Figure 3: '''Power LED, coin for comparison[4]]]		[[File:PowerLEDPicturewithCoin.jpg\|500px\|thumb\|center\|'''Figure 3: '''Power LED, coin for comparison [4]]]

	With a 5V power supply, the circuit’s ballast resistor needed to accommodate a 1.2V drop with 750mA of current. Using standard values and +/- 5% tolerances, a 1ohm power resistor was selected. The circuit schematic follows below.		With a 5V power supply, the circuit’s ballast resistor needed to accommodate a 1.2V drop with 750mA of current. Using standard values and +/- 5% tolerances, a 1ohm power resistor was selected. The circuit schematic follows below.

imported>Student2018: /* Power LEDs */

2018-12-15T04:48:30Z

Power LEDs

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	===Power LEDs===		===Power LEDs===

	[[File:PowerLEDSpecs.png\|600px\|thumb\|center\|'''Figure 3: '''Power LED Specifications [2]]]		[[File:PowerLEDSpecs.png\|600px\|thumb\|center\|'''Figure 3: '''Power LED Specifications [4]]]

	iPixel LED’s 3W “warm white” (3000-3300nm) power LEDs packaged on an aluminum-backed PCB base were chosen for their availability and ease of use. According to the provided datasheet, each LED had an expected forward current of 750 mA with an absolute maximum of peak pulsed forward current of 3A. In addition, the worst-case forward voltage drop across the LED is 3.8V while the minimum voltage drop is 3.2V.		iPixel LED’s 3W “warm white” (3000-3300nm) power LEDs packaged on an aluminum-backed PCB base were chosen for their availability and ease of use. According to the provided datasheet, each LED had an expected forward current of 750 mA with an absolute maximum of peak pulsed forward current of 3A. In addition, the worst-case forward voltage drop across the LED is 3.8V while the minimum voltage drop is 3.2V.

	[[File:PowerLEDPicturewithCoin.jpg\|500px\|thumb\|center\|'''Figure 3: '''Power LED, coin for comparison[3]]]		[[File:PowerLEDPicturewithCoin.jpg\|500px\|thumb\|center\|'''Figure 3: '''Power LED, coin for comparison[4]]]

	With a 5V power supply, the circuit’s ballast resistor needed to accommodate a 1.2V drop with 750mA of current. Using standard values and +/- 5% tolerances, a 1ohm power resistor was selected. The circuit schematic follows below.		With a 5V power supply, the circuit’s ballast resistor needed to accommodate a 1.2V drop with 750mA of current. Using standard values and +/- 5% tolerances, a 1ohm power resistor was selected. The circuit schematic follows below.

	[[File:LEDSchematic.png\|500px\|thumb\|center\|'''Figure 4:''' LED Schematic]]		[[File:LEDSchematic.png\|500px\|thumb\|center\|'''Figure 4:''' LED Schematic, generated with KiCad]]

	Under these test conditions, resultant current from the test circuit was 1.1-1.3A with worst-case fluctuation of 20 mA. Furthermore, significant heat was emitted to the point that some adhesive used to secure the LED had begun to warp. Although these findings were expected, both the current fluctuation and emitted heat had to be controlled before further work could be done.		Under these test conditions, resultant current from the test circuit was 1.1-1.3A with worst-case fluctuation of 20 mA. Furthermore, significant heat was emitted to the point that some adhesive used to secure the LED had begun to warp. Although these findings were expected, both the current fluctuation and emitted heat had to be controlled before further work could be done.

imported>Student2018: /* Area Uniformity Metrics */

2018-12-15T04:48:02Z

Area Uniformity Metrics

← Older revision		Revision as of 04:48, 15 December 2018
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	===Area Uniformity Metrics===		===Area Uniformity Metrics===
	The Information Display Measurements Standard (IDMS)[2] describes multiple methods for area uniformity analysis. The simplest method described is to sample a series of point along a diagonal, horizontal, or vertical line through the center of the image and then plotting pixel value as a function of distance. One optimization the IDMS offers is to plot the image’s pixel values as a surface or mesh plot with an associated colormap, providing a 3D view of the image’s uniformity. The IDMS also proposes another imaging method based on contrast ratios. For this method, white and black luminance data for the display in question must be acquired. Once the two images are acquired, the IDMS proposes an algorithm to calculate a contrast ratio for each pixel; then, the contrast ratios per pixel are rendered in a 2D plot to identify points of non-uniformity. This method works well for displays to identify aberrations in its surface. A more generalizable method to images is to calculate the RMS value of the screen, the minimum value of the screen, and the maximum value of the screen. Once completed, the maximum deviation from the mean can be calculated by taking the maximum of: <br/>		The Information Display Measurements Standard (IDMS)[3] describes multiple methods for area uniformity analysis. The simplest method described is to sample a series of point along a diagonal, horizontal, or vertical line through the center of the image and then plotting pixel value as a function of distance. One optimization the IDMS offers is to plot the image’s pixel values as a surface or mesh plot with an associated colormap, providing a 3D view of the image’s uniformity. The IDMS also proposes another imaging method based on contrast ratios. For this method, white and black luminance data for the display in question must be acquired. Once the two images are acquired, the IDMS proposes an algorithm to calculate a contrast ratio for each pixel; then, the contrast ratios per pixel are rendered in a 2D plot to identify points of non-uniformity. This method works well for displays to identify aberrations in its surface. A more generalizable method to images is to calculate the RMS value of the screen, the minimum value of the screen, and the maximum value of the screen. Once completed, the maximum deviation from the mean can be calculated by taking the maximum of: <br/>
	1) difference between RMS value and maximum value <br/>		1) difference between RMS value and maximum value <br/>
	2) difference between RMS value and minimum value <br/>		2) difference between RMS value and minimum value <br/>

imported>Student2018: /* References */

2018-12-15T04:47:46Z

References

← Older revision		Revision as of 04:47, 15 December 2018
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	==References==		==References==

	[1]http://www.forenscope.com/products/dental		[1]http://www.forenscope.com/products/dental <br/>
	[2]https://www.amazon.com/dp/B00AY0J4OY/ref=cm_sw_r_pi_dp_B1Lqwb0FDFP5A<br/>		[2]https://www.amazon.com/dp/B00AY0J4OY/ref=cm_sw_r_pi_dp_B1Lqwb0FDFP5A<br/>
	[3] Information Display Measurements Standard. Society for Information Display, 2012, pp. 139–149, Information Display Measurements Standard. <br/>		[3] Information Display Measurements Standard. Society for Information Display, 2012, pp. 139–149, Information Display Measurements Standard. <br/>

imported>Student2018: /* Power LEDs */

2018-12-15T04:47:32Z

Power LEDs

← Older revision		Revision as of 04:47, 15 December 2018
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	===Power LEDs===		===Power LEDs===

	[[File:PowerLEDSpecs.png\|600px\|thumb\|center\|'''Figure 2: '''Power LED Specifications[3]]]		[[File:PowerLEDSpecs.png\|600px\|thumb\|center\|'''Figure 3: '''Power LED Specifications [2]]]

	iPixel LED’s 3W “warm white” (3000-3300nm) power LEDs packaged on an aluminum-backed PCB base were chosen for their availability and ease of use. According to the provided datasheet, each LED had an expected forward current of 750 mA with an absolute maximum of peak pulsed forward current of 3A. In addition, the worst-case forward voltage drop across the LED is 3.8V while the minimum voltage drop is 3.2V.		iPixel LED’s 3W “warm white” (3000-3300nm) power LEDs packaged on an aluminum-backed PCB base were chosen for their availability and ease of use. According to the provided datasheet, each LED had an expected forward current of 750 mA with an absolute maximum of peak pulsed forward current of 3A. In addition, the worst-case forward voltage drop across the LED is 3.8V while the minimum voltage drop is 3.2V.

imported>Student2018: /* Background */

2018-12-15T04:47:20Z

Background

← Older revision		Revision as of 04:47, 15 December 2018
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	Photographers use LED-based ring lights to control illumination of a target. These ring lights take the form of an annulus with an inner radius sufficiently large enough to accommodate a camera lens. One example of such a product is shown below:		Photographers use LED-based ring lights to control illumination of a target. These ring lights take the form of an annulus with an inner radius sufficiently large enough to accommodate a camera lens. One example of such a product is shown below:

	[[File:LEDRingLight.jpg\|350px\|thumb\|center\|'''Figure 1:''' LED Ring Light[1]]]		[[File:LEDRingLight.jpg\|350px\|thumb\|center\|'''Figure 2:''' LED Ring Light [2]]]

	The illumination system for the multispectral imager will have a similar form factor to the above figure in order to enhance the uniformity of the output light.		The illumination system for the multispectral imager will have a similar form factor to the above figure in order to enhance the uniformity of the output light.