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18 votes

What do system LEDs signify?

Current RPi models have some of the following LEDs: PWR (red) Indicates that power has been provided to the board. On A+ and later models it will flash if the voltage drops below 4.63V ACT (green) ...
Dmitry Grigoryev's user avatar
12 votes
Accepted

Are there other act_led_trigger options besides "mmc" and "heartbeat"?

I have tried describing the values mentioned. none No trigger kbd-scrolllock Keyboard scroll lock kbd-numlock Keyboard num lock kbd-capslock Keyboard caps lock kbd-...
Ameer's user avatar
  • 405
11 votes

Is there any built in LED connected with GPIO pin?

Yes, it is possible to control the built-in leds. Green LED is easier. According to here, though it is probably Pi 3 specific, since it didn't work for my Pi 4: In the terminal: sudo echo 1 > ...
Botspot's user avatar
  • 1,779
10 votes
Accepted

Power LED from 3.3V Power Pin without Resistor

You need to consider that the forward voltage of a white LED is likely in the range of 3.0 V to 3.2 V (according to the linked article). Assuming the best case of 3.0 V and a resistor of 330 Ohms and ...
Ghanima's user avatar
  • 15.9k
9 votes

2nd LED not working when connected to different GPIO port

LEDs have different characteristics depending on their color. Of significance is the so called forward voltage. Blue LEDs have a typical forward voltage of 3.3V to 3.4V which is higher than the ...
Ghanima's user avatar
  • 15.9k
9 votes

Is there any built in LED connected with GPIO pin?

though it is probably Pi 3 specific, since it didn't work for my Pi 4 It works on the 4 as well, you just need to set the right trigger. The instructions that you provided are not applicable to the 4 ...
icuwopcui's user avatar
8 votes

I can't get three LED lights to turn off and on in an order

You need to set the pin as an output before you use it. To do that add the following line: GPIO.setup(red, GPIO.OUT) below the matching lines for green and yellow: GPIO.setup(yellow, GPIO.OUT) ...
Steve Robillard's user avatar
7 votes
Accepted

connecting common anode rgb led

Connect the common anode pin to 3.3 volt and each of the other pins to a GPIO (add a current limiting resistor between the LED and the GPIO pin. To Light one of the colors set the corresponding GPIO ...
Steve Robillard's user avatar
7 votes
Accepted

What is the maximum number of RGB LEDs that can be controlled individually?

Actually, with 17 GPIOs you can drive 72 LEDs using time multiplex (8 groups of 9 LEDs are driven one after another for such a short time that our eyes believes they are on at the same time, just less ...
Philippos's user avatar
  • 230
5 votes
Accepted

Powering up a WS2812 led strip with different power supplies

I'm presuming that WS2818 is a typo. For the most part your setup sounds fine. The only thing I'd change would be the connection between the LED strip and the Pi. WS281[x] chips, strictly speaking, ...
goobering's user avatar
  • 10.7k
5 votes
Accepted

Light a led without GPIO board

Yes, You can connect LEDs directly to Pi's pins. The Pi has many GPIOs on the header and you can use any one of them and connect an LED on a breadboard. Here is one very well explained tutorial for ...
HallMark's user avatar
5 votes
Accepted

RPI GPIO Ports default on?

Yes, it is normal. GPIO 0-8 have their internal pulls to 3V3 enabled at boot. That will allow enough current to flow to dimly light a LED.
joan's user avatar
  • 71.1k
5 votes

Are there other act_led_trigger options besides "mmc" and "heartbeat"?

Try any of the values in cat /sys/devices/platform/leds/leds/led0/trigger
Milliways's user avatar
  • 60.3k
5 votes
Accepted

Pi Zero W - Switching camera LED from program or command line

After much searching I attempted to use an overlay as detailed here https://github.com/raspberrypi/linux/issues/1332 however on checking the source dts file it appears that the camera led for the pi ...
Charemer's user avatar
  • 645
5 votes
Accepted

Turn on a Led with Raspberry Pi

The Raspberry Pi GPIO header has 40 pins. There are two 5V pins, two 3V3 pins, some ground pins, and the rest are general purpose - you can use them as input or output pins. These general pins are ...
ben_nuttall's user avatar
  • 2,461
5 votes
Accepted

Dimming a 0-10v dimmable light

For 0-10V DC Dimming, 0V does not equate to 0 light output. The dimming ballast or drivers are rated for a 10-100% or 1-100% dimming range. To turn the fixture completely off, you also need a relay ...
Adam Geron's user avatar
5 votes
Accepted

How can Rpi Python PWM GPIO pins control PT4115 to dim LED strips of 1W 350mA?

Question How can Rpi Thonny Python PWM GPIO pins control brightness of white LED strips of 3 to 4 1W 350mA power LEDs? It would be nice to start easy with a cheap module, and later do a DIY project ...
tlfong01's user avatar
  • 4,695
4 votes

Why is a resistor needed for LEDs?

The Question: Why is a resistor even needed, and how would you know what ohms it should be? The Short Answer: A resistor is not needed. The parameter of primary importance is the current to be ...
Seamus's user avatar
  • 22.2k
4 votes

How to blink LEDs on/off continually, while continuing execution of a script?

I'm relatively new to Python, but I have been able to flash the LEDs while continuing execution by using Pulse Width Modulation(PWM) which is built into the RPi.GPIO module. This in my opinion was a ...
josxou15's user avatar
4 votes
Accepted

How to calculate how many watts a resistor need?

Watts(P) are the product of Voltage(V) and Amperage/Current(I). So if this is hooked up to the GPIO of the RPi, you know V=3.3V (assuming you didn't wire this up to the 5V pin). Assuming the LED has a ...
Phil B.'s user avatar
  • 5,043
4 votes
Accepted

Powering WS2812B LED strip from Pi brownouts

Powering the Pi using the pins at the GPIO connector and connecting the LEDs at the other pins of the same connector bypasses the Pi's protective circuitry that could not handle that much current. ...
Ghanima's user avatar
  • 15.9k
4 votes

What is the maximum number of RGB LEDs that can be controlled individually?

Yes and no. If you are talking about discrete LEDs then yes each one will need 3 pins and a common power or ground connection. However, they also make individually addressable RGB LED strips, rings ...
Steve Robillard's user avatar
4 votes

Pi 3 extend the green status led

If you have to ask this question you almost certainly do not have the tools to perform this task, which would be a bad idea. Putting LEDS in parallel seldom works, and it would be a difficult task. ...
Milliways's user avatar
  • 60.3k
4 votes
Accepted

Why optocoupler (4N35) needs resistor?

Inside the optocoupler is an IR LED on one side (between pins 1 and 2) in the image below and a phototransistor on the other (pins 4, 5 and 6). And so the resistor is there for exactly the same ...
Steve Robillard's user avatar
4 votes

How complicated is it to light an LED?

No, it's not more complicated. Getting your first program to run (and work) can sometimes be a bit confounding. It could be my eyes, but it looks like you're connected to pin 4 (+5v) and pin10 (...
tbitson's user avatar
  • 161
4 votes
Accepted

How many MAX7219 8x8 can a Raspberry Pi 3 power?

From the 5 V pin, you can draw as much current as your power supply allows, as stated on eLinux: Maximum permitted current draw from the 5 V pin is the USB input current (usually 1 A) minus any ...
Aurora0001's user avatar
  • 6,328
4 votes
Accepted

How to turn off pin 23 correctly? SSH connection crashed

Assuming your SSH session is restored, otherwise reboot ... On the standard terminal command line: gpio -g mode 23 out gpio -g write 23 0 From Python: import RPi.GPIO as GPIO GPIO.setmode(GPIO.BCM) ...
John Hawthorne's user avatar
4 votes
Accepted

How to control 12V LED with the GPIO?

As per your requrement if your LED supply is 12v then you can't connect LED directly to GPIO pins. Because it only give 3.5v & 50mA at output. Simply you connect driver circuit between LED and ...
pranav patil's user avatar
4 votes

Powering 100mA LED

OP asked, "... any boards available for this purpose?" This seems more of a "shopping question" than a technical question, but I'll try to answer it to provide some ideas on what you may want to ...
Seamus's user avatar
  • 22.2k
4 votes

Controlling LED strip from GPIO Help?

Make sure you have a common ground between the Pi, the LEDs and the power supply so that referenced voltages are consistent.
CoderMike's user avatar
  • 6,987

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