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diff --git a/blog/led-characterization/index.html b/blog/led-characterization/index.html index 294b090..4c0f8fc 100644 --- a/blog/led-characterization/index.html +++ b/blog/led-characterization/index.html @@ -16,6 +16,9 @@ <a href="/projects/" title="Projects">Projects</a> <a href="/about/" title="About">About</a> </div> + <div class="search"> + <div id="search"></div> + </div> <div class="external"> <a href="https://git.jaseg.de/" title="cgit">cgit</a> <a href="https://github.com/jaseg" title="Github">Github</a> @@ -32,7 +35,7 @@ </ul> <strong>2018-05-02</strong> </header> - <main> + <main data-pagefind-body> <div class="document"> @@ -47,7 +50,7 @@ perception and LED peculiarities.</p> interesting, with up to two RGB or RGBW (red-green-blue-white) LED tapes. For ambient lighting high color resolution was really important so you could dim it down a lot without flickering. I ended up using the same driver stage I used in the <a class="reference external" href="http://jaseg.de/blog/multichannel-led-driver/">multichannel LED driver</a> project for its great color resolution and low hardware requirements.</p> -<figure> +<figure data-pagefind-ignore> <img src="images/rgb_cube.svg" alt="An illustration of the RGB color cube."> <figcaption>An illustration of the RGB color cube. <a href="https://commons.wikimedia.org/wiki/File:RGB_color_cube.svg">Picture</a> by @@ -68,7 +71,7 @@ color. <a class="reference external" href="https://en.wikipedia.org/wiki/HSL_and <em>perceptual</em> color spaces such as <a class="reference external" href="https://en.wikipedia.org/wiki/CIE_1931_color_space">XYZ (CIE 1931)</a> and <a class="reference external" href="https://en.wikipedia.org/wiki/Lab_color_space">CIE Lab/LCh</a> were born, further improving this alignment. In this mathematical model, mapping a color from one color space into another color space is just a coordinate transformation.</p> -<figure> +<figure data-pagefind-ignore> <img src="images/hsv_cylinder.png" alt="An illustration of the HSV color space as a cylinder."> <figcaption>An illustration of the HSV color space as a cylinder. <a href="https://commons.wikimedia.org/wiki/File:HSV_color_solid_cylinder.png">Picture</a> by @@ -83,7 +86,7 @@ XYZ. The fat white curve is a projection of the <em>monochromatic spectral locus XYZ for pure visible wavelengths.</p> <p>As you can see, sRGB is <em>much</em> smaller than XYZ or even the part within the monochromatic locus that we can perceive. In particular in the blues and greens we loose <em>a lot</em> of colors to sRGB.</p> -<figure> +<figure data-pagefind-ignore> <video controls loop> <source src="video/sRGB.mkv" type="video/h264"> <source src="video/sRGB.webm" type="video/webm"> @@ -108,7 +111,7 @@ In practice, the blue channel of my RGB tape to me <em>looks</em> much brighter may be of a slightly different hue compared to the reference red used in <a class="reference external" href="https://en.wikipedia.org/wiki/SRGB">sRGB</a> which would also skew the RGB color space.</li> </ul> -<div class="subfigure"> +<div class="subfigure" data-pagefind-ignore> <figure> <img src="images/driver_ringing_strong.jpg" alt="Strong ringing on the LED voltage waveform edge at about 100% overshoot during about 70% of the cycle time."> @@ -160,7 +163,7 @@ specific to the semiconductor used and is quite precise. White LEDs are in fact and re-emits a broader spectrum of more yellow-ish wavelengths instead. The final LED spectrum is a superposition of both spectra, with some of the original blue light leaking through the phosphor mixing with the broadband yellow spectrum of the phosphor.</p> -<div class="subfigure"> +<div class="subfigure" data-pagefind-ignore> <figure> <img src="images/spectrograph_step1_parts.jpg"> <figcaption>The ingredients. The cup of coffee and Madoka Magica DVD set are essential to the eventual @@ -188,7 +191,7 @@ spectrum of the phosphor.</p> flaw: I wanted to acquire quantitative measurements of brightness across the spectrum. Since I don't have a precise technical datasheet specifying the spectral response of any of my cameras I can't compare the absolute brightness of different colors on their pictures. Some other sensor was needed.</p> -<figure> +<figure data-pagefind-ignore> <img src="images/daylight_spectrum_dvd.jpg"> <figcaption>The daylight spectrum as seen using a DVD as a grating. <a href="https://commons.wikimedia.org/wiki/File:SpectresSolaires-DVD.jpg">Picture</a> by @@ -219,7 +222,7 @@ rejection and a regular non-inverting amplifier using another op-amp from the sa transimpedance amplifier output. I put all the passives setting amplifier response (the gain-setting resistors and the filter resistor and capacitors) on a small removable adapter so I could easily change them if necessary. I put a small trimpot on the virtual ground both amplifers use as a reference so I could trim that if necessary.</p> -<figure> +<figure data-pagefind-ignore> <img src="images/preamp_schematic.jpg" alt="A drawing of the photodiode preamplifier's schematic"> <figcaption>The photodiode preamplifier schematic. Schematic drawn with an unlicensed copy of DaveCAD.</figcaption> @@ -232,7 +235,7 @@ SMD-to-DIP adapter.</p> <p>Flying-wire construction is just fine for this low-frequency circuit. In a high-speed photodiode preamp, the transimpedance amplifier circuit would be highly sensitive to stray capacitance, but we're not aiming at high speed here.</p> -<div class="subfigure"> +<div class="subfigure" data-pagefind-ignore> <figure> <img src="images/preamp_front.jpg"> <figcaption>The front side of the preamplifier board.</figcaption> @@ -258,7 +261,7 @@ this wire does not put too much strain on it.</p> the linear stage in front of the spectrometer viewing window. A line on the screen paper points to the photodiode die in parallel to the linear stage allowing precise alignment.</p> <p>The whole unit with photodiode preamplifier, linear stage, photodiode and stepper motor driver finally looks like this:</p> -<figure> +<figure data-pagefind-ignore> <img src="images/electronics_whole.jpg" alt="The complete electronics setup of the spectrograph. In the back there is the DVD drive stepper stage. In front of it, mounted on a piece of wood are a small USB-to-12V switching-regulator module to power the stepper motor in the top left, below on the bottom left is the @@ -295,7 +298,7 @@ notebook is capable of live-updating a graph with the in-progress spectrum's dat check for when I made some mistake easy to spot in the resulting data.</p> <p>After one color channel is captured, the LED tape has to be manually set to the next color and the next measurement can begin.</p> -<figure> +<figure data-pagefind-ignore> <img src="images/raw_plot_cheap_rgb.svg" alt="A plot with three wide peaks, two large peaks on both sides and one smaller one in the middle. The middle one overlaps the two on the sides. The large ones are about 2.5V in amplitude. Overall, the plot is about 300 stepper steps wide with each peak being around 130 steps wide."> @@ -324,7 +327,7 @@ estimate of the three colors' peaks' locations and widths.</p> <p>The photodiode's response is strongly wavelength-dependent. In particular in the blue band, the photodiode's sensitivity gets very poor down to about 20% at the edge to ultraviolet. This effect is strong enough to move the apparent location of the blue peak towards red.</p> -<figure> +<figure data-pagefind-ignore> <img src="images/photodiode_sensitivity.svg" alt="A plot of photodiode sensitivity against wavelength relative to peak sensitivity at 820nm. The sensitivity rises from 20% at 380nm approximately linearly to 80% at 620nm, then the rise rolls off."> @@ -338,7 +341,7 @@ using this coarse measurement. Then all three channel peaks are measured in the estimate is produced by a least-squares fit of a linear function. This fine estimate is then used for a second sensitivity correction of all original measurements and the scale is changed from stepper motor step count to wavelength in nanometers.</p> -<figure> +<figure data-pagefind-ignore> <img src="images/processed_plot_cheap_rgb.svg" alt="A plot with three wide peaks, all three of different heights. The leftmost peak is highest at 6nA, the middle peak lowest at 1.6nA and the rightmost peak in between at 4nA. The middle one overlaps the two on the sides. Overall, the plot spans about 300nm on its x axis with @@ -365,7 +368,7 @@ space (colorful) as well as sRGB (white) for comparison plotted within CIE 1931 both so for this illustration the LED color space has been scaled to fit. These figures were made with blender and a few lines of python. The blender project file including all settings and the python script to generate the color space models can be found in the <a class="reference external" href="https://github.com/jaseg/led_drv">project repo</a>.</p> -<figure> +<figure data-pagefind-ignore> <video controls loop> <source src="video/led_within_srgb_scale=1.0.mkv" type="video/h264"> <source src="video/led_within_srgb_scale=1.0.webm" type="video/webm"> @@ -419,13 +422,18 @@ can view the Jupyter notebook most of the analysis above <a class="reference ext / <a href="/about/">About</a> / <a href="/imprint/">Imprint</a> </footer> -<script> +<script src="/pagefind/pagefind-ui.js"></script> + <script> if(navigator.getEnvironmentIntegrity!==undefined)document.querySelector('body').innerHTML=`<h1>Your browser contains Google DRM</h1>"Web Environment Integrity" is a Google euphemism for a DRM that is designed to prevent ad-blocking, and which Google has forced into their browsers against widespread public opposition. 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