60 votes
Accepted

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 ...
winny's user avatar
  • 14.7k
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 ...
Justme's user avatar
  • 149k
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 ...
IceGlasses's user avatar
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 ...
Peter Bennett's user avatar
13 votes
Accepted

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 ...
Simon Marcoux's user avatar
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 ...
Passerby's user avatar
  • 73k
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 ...
ajb's user avatar
  • 3,414
10 votes
Accepted

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 ...
Misunderstood's user avatar
9 votes
Accepted

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 ...
Kuba hasn't forgotten Monica's user avatar
9 votes
Accepted

RGB digital to analog converter

WS2812 protocol is based on different high/low times to encode bits, it's non standard, and pretty fast (~1-2µs/bit). You could use a microcontroller but it will have to run code in a tight loop to ...
bobflux's user avatar
  • 77.5k
8 votes
Accepted

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 ...
Trevor_G's user avatar
  • 46.7k
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. ...
Passerby's user avatar
  • 73k
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 ...
Spehro Pefhany's user avatar
7 votes
Accepted

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. ...
Bruce Abbott's user avatar
  • 56.4k
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 ...
hacktastical's user avatar
  • 54.1k
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 ...
Dampmaskin's user avatar
  • 3,797
6 votes

Issues driving 3W RGB LED (common anode): Can't light all 3 colors at once

It is not going to work quite this way. The diode with the lowest forward voltage (red<green<blue) will hog the lion's share of the current when you try to operate more than a single one at once....
greybeard's user avatar
  • 1,811
6 votes

Why my 12V RGB LED strip controlled by Arduino Uno has reversed colors and when I set RGB to 0,0,0 (after reverse) strip should be black but its red?

Looks like you have a pictorial diagram that is intended to use N-channel MOSFETs and you've subsituted BD912 PNP transistors (without base resistors). If accurate, that's not going to work and you ...
Spehro Pefhany's user avatar
5 votes

What resistor to use with this RGB LED?

This answer doesn't take into consideration the lumens per mA of each color of LED. Looking at the datasheet for the Cree ds-UHD1110-FKA color LED, page 2 shows the typical electrical and optical ...
Mark Stokes's user avatar
5 votes

Building a simple USB notification light

A USB port can't speak WS2812, you need something else to convert something that USB can send into something that WS2812 understands. It may be possible to port fastled's UART code to pc and use a ...
Jasen  Слава Україні's user avatar
5 votes
Accepted

Why does pixel binning remove colors and provide monochrome image only with CMOS color cameras?

It could be because of the Bayer (color filter) array, although that depends on the camera manufacturer making a particular set of decisions. Adjacent pixels have filters in front of them that make ...
hobbs's user avatar
  • 7,415
5 votes
Accepted

How to manage MOSFET spikes in low side switch switch

The MOSFET gates are tiny capacitances, which depending on the model, range from a picofarads to nanofarads. The AO4630 device has a gate capacitance of over 500pF. Every time one of your voltage ...
Simon Fitch's user avatar
  • 35.2k
5 votes
Accepted

Control WS2812B LEDs independently

Yes there is a way. You just send new data packet to all LEDs, but with only the changes for the LEDs you want to change. Even if you don't want to change the other LEDs, you need to update their data ...
Justme's user avatar
  • 149k
5 votes
Accepted

Why the LED heats up and fails to pass the controlling information further?

I think there are many things not entirely correct. First of all, it is a miracle that you can use that logic level shifter at all. Most people here simply ask why it does not work level translating a ...
Justme's user avatar
  • 149k
4 votes

Single supply op amp that can swing -0.3v and output -0.6v

There is no op-amp that can drive its output below its negative supply rail. Alternative approaches include using a charge pump chip to generate a negative supply rail for your op-amp or offsetting ...
The Photon's user avatar
  • 130k
4 votes
Accepted

Diode destroys square wave?

The simulation looks basically correct. The gate of the MOSFET acts a small capacitor, so each channel's circuit looks like this: simulate this circuit – Schematic created using CircuitLab ...
Abe Karplus's user avatar
  • 2,621
4 votes

How much current do I need for a 5050 RGB strip?

The manufacturer or supplier should specify current per length of strip. As a "rule of thumb" most small LEDs are rated at 20 mA and groups of 3 are connected in series plus a series resistor to 12V. ...
Russell McMahon's user avatar
  • 150k
4 votes
Accepted

Why is my RGB LED strip passing current through the transistor?

You need a LOW side switch. Use NPN transistors instead of PNP. Use a 10 K pull-down resistor at base to prevent false turn ONs due to noise.
Whiskeyjack's user avatar
  • 8,286
4 votes

How to manage MOSFET spikes in low side switch switch

In the simulation, there is no inductance or resistance in any of the wires. Capacitors and wires are superconducting. If you want to make the simulation behave like a real world circuit, then put in ...
Voltage Spike's user avatar
  • 82.5k
4 votes

Issues driving 3W RGB LED (common anode): Can't light all 3 colors at once

You have all the LEDs sharing a single current limit resistor, and that will not work as you have seen. As blue LED requires more voltage than red LED, and if you try to turn both LEDs on they will be ...
Justme's user avatar
  • 149k

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