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Topic: Question about Multiple LEDS on one GPIO Pin (Read 385 times) previous topic - next topic

skiedude

In my basic understanding and googling around, from what I can tell you shouldn't chain multiple LEDs across a single GPIO pin due to power constraints. In an effort to make a DIY 'wake up' clock for my kids I stumbled across https://www.instructables.com/id/OK-to-wake-light-with-automated-clock/ , looking at his circuit diagram, from what I can tell all the Green LED are all on the same GPIO pin.



Am I misunderstanding his design?

Wawa

#1
May 12, 2020, 05:49 am Last Edit: May 12, 2020, 05:52 am by Wawa
Yes, you shouldn't build anything from destructables unless you know what you're doing.

The LEDs are set for ~20mA each with the 150 ohm resistors.
That's theoretically 100mA per output pin, which is 2.5 times over the absolute max.
Shows you that 5volt Arduinos are tough cookies.

Other bad things is that a 7-12volt supply on the DC socket is recommended.
And that a servo is powered from the 5volt pin.

The use of resistors with the buttons is an indicator that this dude is still a beginner.

Avoid making this if you want things to last.
Leo..

MK1888

And if you want to switch a bank of LEDs from the Arduino like that you'd use a transistor.

skiedude

Thank you both for the reply. My intention was not to debunk this authors instructable, was just to understand. I did come across another similar one that seems more straight forward with my beginner knowledge as well. https://www.instructables.com/id/Green-Means-Go-10-Light-Up-Clock-for-Kids/

Thanks!

Paul__B

My intention was not to debunk this authors instructable, was just to understand.
And there is the point.  :smiley-eek:

This is an example of the great danger in using any so-called "information" from that site.

There is specifically, no provision for review or commentary, so all errors - and they are frequent - go unchallenged forever as a snare for the "newbie" such as yourself.  In fact, it is perverse that you really should only use the site if you already are fully competent in electronic design!

skiedude

While not to totally derail this thread, but one final post, with that information in mind, where is a good place for a newbie like me to get the right information to start with

Grumpy_Mike

#6
May 13, 2020, 07:47 am Last Edit: May 13, 2020, 07:49 am by Grumpy_Mike
Quote
from what I can tell you shouldn't chain multiple LEDs across a single GPIO pin
The word "chain" implies a series circuit, what you have here is a parallel circuit, so it is wrong to call it chain.

A good source of information is the resellers / manufacturers for the hobbyists, such places as Adafruit and Sparkfun have tutorials that are on the whole reliable. Also look for sites with no advertising as that is a clue to them being independent and not wanting to make money from what they are telling you.

I have my own website which covers some aspects of the hobby, these are aimed not at an absolute beginner but a step up from that. Also seek out Nick Gammon's site, that is more of a narrative style, looking like a forum but it is also very good information.
https://gammon.com.au/forum/bbshowpost.php?bbtopic_id=123

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