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55 votes
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Why can't RGB or bicolour LEDs produce a decent yellow?

Most probably because of short wavelength of your green LED and not as monochromatic green as you might expect (x and y coordinates closer to the center). If you take a look at the CIE 1931 curve and ...
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30 votes

My DIY RGB LED panel powered by 9V battery works but certain colors like blue, white, and purple don't work

It is a bit hard to see from the picture, but since each LED has six pins, and knowing that it is meant for 12V supply, it is extremely likely that the LEDs might be arranged so that there are three ...
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29 votes
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Why are the three component LEDs in an RGB LED so unbalanced?

Sounds about right. To get white (6500K) using NTSC (colour TV) phosphors, the relative intensities are G=0.59, R=0.3, B=0.11 - most of the energy is in the green, least in the blue. (slightly ...
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19 votes

Why can't RGB or bicolour LEDs produce a decent yellow?

It's even a little worse than winny indicates: Green LEDs are finicky. One result is that green LEDs emit over a broader distribution of wavelengths instead of being a nearly laser-like single ...
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19 votes

My DIY RGB LED panel powered by 9V battery works but certain colors like blue, white, and purple don't work

Blue LEDs require a higher voltage than red and green. If the panels are designed to work on 12 V, there may not be enough voltage to light the blue LEDs when run on 9 V. The blue LEDs must work for ...
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17 votes

Why are the three component LEDs in an RGB LED so unbalanced?

I do not claim the other answers are wrong, but they miss two important points. One of them that I consider the most relevant. RGB-LEDs are not meant to produce white light. They are meant to reach a ...
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16 votes
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Why does a resistor in my Neopixel data line work at all?

The resistor is there to limit the current into the input pin. The input likely has a very high DC resistance (more than 1 megohm) so negligible current flows (on the order uA) and a negligible ...
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15 votes
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Why must resistors be on the respective anode terminals instead of the common cathode terminal of a RGB LED?

The red led will hog all the current because it might only need 2 volts across it to begin conducting. The green and blue LEDs need a higher voltage but because they are all in parallel the red led ...
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13 votes
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Can I replace these many capacitors with just one?

The goal of each capacitor here is to smooth out the power supply of each WS2812B. When you power an array of LEDs, there is a good chance that a transient voltage drop will occur and create a ...
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11 votes

Can I replace these many capacitors with just one?

Those caps are small bypass capacitors, use to filter or buffer the voltage input to an IC. They are cheap and useful and you will find them as close as possible to any IC on any manufactured pcb ...
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10 votes

Can I replace these many capacitors with just one?

These are "decoupling" or "bypass" capacitors. Their purpose is to stabilize the local supply voltage against fluctuations caused by the interaction of varying current consumption in the circuit with ...
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10 votes
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What is the RGB value of Edison Light Bulbs?

I used Firefox Web Developer Eyedropper to grab the RGB from a photo of an Edison Light Bulb. #FACA08 (250,202,8) A lighter pixel This is very close to the color when a 2700K 97 CRI LED was ...
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9 votes
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Building a simple USB notification light

The cable is just that... a cable. The ring light doesn't have a USB interface. The Arduino's role was to interface between USB and the light. You need to keep either some Arduino, or another ...
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8 votes
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Why do LEDs have only RGB (Red, Green, Blue) colors why not others?

LEDS actually come in all colours. However, what we as humans call colour is dictated by the fact that the cones in the human eye are only actually sensitive to three primary groups of wavelengths ...
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8 votes

My DIY RGB LED panel powered by 9V battery works but certain colors like blue, white, and purple don't work

Without knowing the schematic im going to just guess these are standard 5050 leds put in a 3 led series setup. For purple you need Red and Blue 100% on. For white you need Red Green and Blue 100% on. ...
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7 votes

Why must resistors be on the respective anode terminals instead of the common cathode terminal of a RGB LED?

For a single LED you are correct - which side you put it on does not matter. However, an RGB LED is a rather different animal since one side of all of the elements are tied together. This presents a ...
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7 votes

Why are the three component LEDs in an RGB LED so unbalanced?

LEDs of different colors are made with quite different materials and processes and designs. There's no guarantee that they'll turn out to be the same brightness. It makes more sense to put more ...
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7 votes
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Single supply op amp that can swing -0.3v and output -0.6v

Composite video signals are usually AC coupled, so you shouldn't need to pull the output below ground. The receiving end will restore the DC level (using the sync pulse as a reference) if it needs to. ...
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7 votes

How much does an op-amp delay?

Using an LTspice simulation with 100 MHz 0.5 V peak sine wave input and the Figure 36 unity gain buffer (+/-5 V supplies), and a 20 pF load, I get about 130 ps. You can see ...
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7 votes

Why would an RGB LED still glow with only the cathode side connected?

LEDs, like all diodes, have reverse leakage current. Because of this leakage, with the common anode left open, if one or more of the cathodes is at a positive voltage (that is, the 'off' state) the ...
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6 votes
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Change RGB leds intensity?

Start by scaling the R,G and B by the intensity value, for your example at 50% intensity you would set 15*0.5, 170*0.5, 230*0.5 (7, 85, 115). The LEDs might have different non-linear responses, so ...
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  • 441
6 votes

LDR + RGB Led = Color sensor. How to calibrate it?

You are attempting to map a triplet of values (the responses of the LDR to your RGB LEDs) to another triplet (the RGB values you used to print the colors on the paper). There are loads of ...
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6 votes

Why do LEDs have only RGB (Red, Green, Blue) colors why not others?

Single LEDs come in orange, yellow, amber, infrared, ultraviolet, cold white, warm white and many other colors/hues. Therefore I assume you mean to ask why multicolor LEDs are typically red, green and ...
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5 votes

RGB & Proximity Sensor at about 6 feet

Light sensors aren't limited to any distance. It makes no difference whether the photons they sense came from someone's clothes 1 foot away or the sun 93 Mmiles away. Your problem with distance is ...
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5 votes
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Dimension RGB LED for peak current

The 100mA/10% duty cycle is absolute maximum rating at 25°C ambient temperature. It is not something you should be designing to, and note that it only gives you 10mA average current per LED. It should ...
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5 votes

How a decoded picture is stored in a memory?

Your result isn't a matrix of MxNx3. Your result is a sequence of numbers. You can store them however you like. Take the LCD screen you're reading this on, for instance. That is a 2D device, isn't ...
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5 votes

How does a PC detect a VGA monitor?

Computers detect screens by something called Display Data Channel It's a low rate data signal on four pins in the VGA connector that tells the computer about its presence, allowed modes and ...
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5 votes
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how to get the RGB value of a color using phototransistor or photodiode?

To understand the results you are getting you have to consider the spectral response curves of your light source, detector, and the object being measured. The final result is a combination of all ...
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5 votes
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tricolor single package LEDs do not have same intensity for each color, why?

Simple. Different colors correspond to different wavelengths of light, shorter wavelengths of light require more energy, producing photons of higher energy requires a larger bandgap in the ...
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5 votes
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Use an Arduino to control a 12v rgb strip

Yes. A N-Channel transistor of the right collector current capacity on the R, G & B pins can be used.
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