An LED is a light-emitting diode. Lighting an LED is considered the "Hello world" of a circuit design, and it can be as simple as putting a series resistor or can get more complicated, involving PWM and multiplexing.

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PWM LED using TIM1 on STM32

I need to PWM my LED on STM32F3 Discovery which is on PE8. I have found code which is using PWM on PA8 and PC8 (one using TIM1) but unfortunately I can't change it to PE8. How to do it? Or maybe you ...
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4answers
89 views

How do I find out about the technical details of an LED if I don't have the fact sheet?

I have bought a bunch of LEDs from the rummage table of my local electronics store. Now, I don't have a fact sheet, neither I do know the vendor and / or the article number. How do I find out about ...
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3answers
57 views

Any way to create a 3 LED chaser with only a 555 IC?

I've seen single and dual blinking circuits, but wanted to know if there was some easy way to squeeze in a third? I don't have a 4017 IC at the moment, unfortunately.
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1answer
54 views

light up a 5v led with arduino

I need to build a big 6 digit display using 7 segment displays controlled with an Arduino, but the every display I find uses 5V LEDs like this one: ...
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0answers
29 views

Multiple led fade using charlieplexing at Arduino

Fading single led using charlieplexing is simple (example code). Is it possible to fade all leds independently? (I would like to fade them all simultaneously and randomly with different periods using ...
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1answer
29 views

Minimize Current Sensing Loss in LED Driver

Design voltages and currents: Vo = 100V. Iout = 50mA. Po = 5W. R4 is the output current sense resistor. The reference voltage for the error amplifier is 2.5 V which implies that under the target ...
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1answer
49 views

High Power LED connected to Dry battery

I am new to electronics as i love working with circuits. I have 12V 6W SMD LED, which I want to attach with Battery Powered Driver which currently gives me from 10v-14v DC with 50mAmp. Shall I connect ...
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36 views

Delayed power to led [on hold]

I own a bunch of led lights and I would like to apply power and after 3 or 4 seconds the LEDs would flash once then stay off until the power is disconnected then reconnecting.
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2answers
115 views

Controlling 10 high power LED with a Raspberry Pi

I'm trying to figure out how to control 10 Luxeon Rebel LED (700mA) from a Raspberry Pi. I want to be able to turn them on and off from code, but I don't need to have two or more LEDs turned on at ...
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1answer
49 views

Simple Series Circuit: depending where the resistor is, I get different results. Explanation?

I am building a very simple Series circuit with a better (9V), two LEDs (Red, 5mm) and a resistor (220Ω). See the circuit below. Now, when I connect it all together, here is what happens: 1) (+), ...
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2answers
76 views

Help please! I need to give constant current to an LED from a Lipo battery

I'm trying to drive an LED from a Lipo battery. The useable voltage range of the Lipo goes from 4.2V down to 3.4V, and the forward voltage of the LED is 3.2V. With a resistor in series with the LED, ...
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0answers
51 views

very short range wireless on/off switch [duplicate]

I am in need of suggestions for a wireless on/off switch for my project. I will be using it to trigger an LED and or a sounded alert but am struggling to find one that meets my requirements; It ...
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4answers
113 views

Use transistors to amplify a very small voltage

I'm new to electronics and I have a problem. I want to use a LED to detect light but the voltage it provides is very small (30 mV) and I don't think it can open a transistor. How can I amplify this ...
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1answer
87 views

Using LEDs to indicate if a toilet is occupied or not?

We have two toilets in our office. I want to setup two LEDs in rooms that show which toilet is occupied and which not. How can I do that?
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32 views

Why does a photosensor affect the power factor of an LED

Using a kill-a-watt meter I measured the power factor of my LED light bulb to be 0.60. I then screwed the light bulb into a photosensor that turns the light on at dusk and off at dawn. I re-measured ...
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1answer
118 views

How to Generate Light in the 10,000K Spectrum?

I need to generate a lot of light with the same spectrum as the sun - 10,000 Kelvin (10000K). I have searched around for hours, however all full spectrum lights available are either 5500K or 6500K - ...
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1answer
52 views

I want to wire a single led off a motorcycle battery [duplicate]

I want to use my motorcycle battery to power a single led that has a maximum voltage of 3.6 volts. what resistance do i need to drop the voltage from 12 volt to 3?
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1answer
62 views

How to Convert 20,000 Lumens to Lux?

I need to generate 20,000 lux of light in an indoor environment. I am having trouble converting the lumens to lux using online converters ( I know there are many such converters but the questions they ...
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1answer
20 views

If a meanwell ldh-45 led driver provides a range of voltage outputs at a constant current, how is my desired voltage selected?

http://www.meanwell.com/search/LDH-45/LDH-45-spec.pdf 350mA = current. Lets say my LED forward biases at 42v. Is it a 120 ohm resistor that I need? 42V = 0.35A*120 Ohms I am a bit confused. ...
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1answer
62 views

What does “zo <=500Ω” on the pin diagram means?

There is device (viewfinder). It has "Tally" LED. On the camera's output diagram, on the "Tally OUT Indicator" pin there is marking "zo <=500Ω". What does it mean? Should I supply + voltage on this ...
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1answer
34 views

Dimmer Switch For A NeoPixel Ring

I purchased a set of 4 NeoPixel ring segments and assembled them into a circle. I am trying to create a circular lamp that will be fitted inside a camper van in the ceiling and driven from a 12V ...
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2answers
27 views

Technique to measure/infer Vf for LED given If

This isn't the normal resistor question, and I'm familiar with the theory and Which is better: using a resistor with an LED, or "precisely" matching the Vs to the given LED's Vf rating? ...
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2answers
38 views

Forward current for assorted LEDs

I have an assortment of T1 and T1¾ LEDs from sampler kits and beginner kits. The kits have sketchy documentation, with missing or inaccurate part numbers. I was able to track down datasheets for some ...
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0answers
34 views

multiple RGB LEDS on minimal pwm pins VS current limitions

the theory explained at Hooking up multiple RGB LEDs while using a minimal number of PWM pins on an Arduino? isn't really working with the arduino current limitations mentioned at ...
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2answers
106 views

How to combine two LED indicators (one to VCC, one to GND)

I have two seperate sub-circuits that each have an indicator LED and only one circuit will have power at a time. So far so good, however I would much prefer to have only a single indicator light. My ...
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77 views

What are the different elements on this circuit board?

Can you identify the parts on this thing? I don't understand how it is turning on when I put my finger on it. And besides the LED's, what are the other elements on the board lighting up? Light up ...
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2answers
76 views

How to calculate a electrolytic capacitor based on current and voltage to have the smallest ripple

I have built a circuit involving LEDs powered on 230V AC. The LED current driver that is powered on 30V and contains 10 LEDs of 1W each. 10 of these modules are linked in series and are ...
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1answer
97 views

LED Driver Circuit

I'm building a circuit using a sensor and a "Goldilocks" LED setup. The LEDs are set up to be turned on and off using the outputs from an op-amp, which is wired up in a window detector config. The ...
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2answers
53 views

Calculate resistor for red Led in series

Hello guys i am really confused about the whole resistor issue. I have visited so many sites that tells you what resistor you need but i don't know the volt drop that asks to complete or the current. ...
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0answers
56 views

Really weird AVR issue

So the other day I was changing some fuse bits on a 324p and screwed up. Well I set up a 88A to act as a clock out. Great. Well I went through 4 different chips, including a 48A, because of some ...
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3answers
64 views

What is a suitable candela for a status led?

What is a suitable candela value for a LED to have that doesn't blind you if you stare at it, and will still allow you to view silkscreen markings on the PCB but not to dim that you can see the ...
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2answers
86 views

AC transformer for LED

How do I select the correct transformer (voltage) to drive a series of LED's. Note: I have seen other Questions about this, but not like this here. The voltage for a series of ordinary LED's are ...
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3answers
57 views

Parallel LED strings of different colors and Arduino

I need to use 7 strings of led, each one of a different color. I will control each string using a Arduino and the BC 337 Transistor. The string will be connected to a 12V power supply. I have read ...
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2answers
48 views

led wont turn on in series circuit

I have a bike flash light which is consisted of 5 LEDS (red). Which looks like this. I unsoldered three of them and put it in a series circuit using two AAA bateries. The Leds did not turn on. I ...
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4answers
51 views

LED Driver PFC and Flicker

I have been reading up on LED bulbs and it seems power factor correction (PFC) is quite needed in most designs. My goal is to achieve a PF greater than 0.9. I am considering using an LED Driver with ...
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1answer
51 views

How to power 30 LED 9W downlight?

I bought a cheap LED downlight from ebay. The LED driver (spelt DRINER) that came with it, I do not trust - it is probably dangerous. It states that its output is DC12-24V, 300mA. (which does not add ...
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2answers
51 views

LED circuit:: current goes through, no light

I have made the following circuit. Using the multimeter,+ on first and - on last LED, I get 8.7 volts. What are possible reasons for no light? I have checked that I got the connections correct ( + to ...
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1answer
82 views

powering 12V 5m/16ft 5050 RGB LED Strip with 16V power adapter?

I'm new to the forum found this using google. i have 2 (Two) 5050 RGB 12V LED Strips that are 5M/16ft. It's not as bright as i'd hoped it would be. I double powered one of them with the cheap power ...
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3answers
150 views

Use one or two transistors to switch an LED from PIC

I'm fairly new to electronics - I've had a reasonable amount of success with getting PCBs made using Eagle, but it was mostly wiring together breakouts and fairly simple stuff. I've spend the last two ...
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3answers
112 views

Using a 1.5V battery to increase the voltage from a headphone jack so it can switch a transistor at lower volumes

I recently built a circuit using a 2N3904 BJT transistor with the hopes that when connected to a headphone jack, it would light a LED whenever an audio signal was passed through. However, I found ...
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0answers
57 views

RGB LED array without current limiting resistors but PWM

I found this blog post, where it says: Alternatives to using current limiting resistors: Resistors are a simple way to limit current, but they are not efficient. Excess power is wasted as ...
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1answer
83 views

LED Circuit:: First row doesn't light

I made the bellow circuit on breadboard, but my first row of leds ( each directly after the resistors) is not lighting up. What are the possible reasons for it? I tried swapping leds around and again, ...
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1answer
74 views

Circuit for supporting, common anode AND cathode RGB LED Matrices

I'm designing a driver / controller board for 8x8 RGB LED Matrices that then can be daisy chained to e.g. make an 16x64 Matrix or so. So I came up with a couple of designs that I've tested and so ...
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2answers
45 views

install a dimmer to a non dimmable led strip [closed]

I have a led strip installed. the type is 5050 14.4 watts/meter. I do not know if it is dimmable or not. What happens if i install a dimmer to the strip and it is not dimmable?
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1answer
33 views

problem with LED matrix and raspberry pi

I have a raspberry pi model B+ , and an 8x8 LED matrix(single colored) , so I connected 8 GPIO pins to the 8 row pins of the matrix and another 8 GPIO pins to the 8 colomn pins. Note that I am pretty ...
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4answers
67 views

LED Voltage Drop Confusion

Please take a moment to checkout the simple circuit below: simulate this circuit – Schematic created using CircuitLab As you can see, this is a simple circuit consisting of three LEDs in ...
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2answers
44 views

User power supply current limit to avoid current limiting resistors for LED

everyone! I would like to know if I can avoid to use current limiting resistors by pushing my power supply to its limits (it already sounds not like a good idea... btw...). Say I have a 3.3V power ...
4
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2answers
288 views

LED-lighting problem [closed]

I'm trying to explain some LED-lighting phenomena, that we (me and my family) have observed, while changing light bulbs into LEDs. I've had some courses in semiconductor physics, and I've had a basic ...
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2answers
57 views

Constant Current vs Constant Voltage Dimmable LED Drivers

For my circuit, I want to use 110VAC mains power, via a TRIAC dimmer to an LED Driver power supply. For this use case, I am confused on whether to use a constant voltage AC to DC LED driver power ...
5
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3answers
729 views

Simple, efficient “breathing” LED circuit

I'm currently working on a small circuit, which I intend on running off a CR2032. The intent is to have the circuit last at least 2 weeks (the longer the better), pulsing a green LED every 3 seconds, ...