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Topic: Bad Tutorial? Connect an LED directly to pin 13 without resistor? (Read 743 times) previous topic - next topic

rtek1000

Hello,

Connect an LED directly to pin 13 without resistor?  :o

How can a tutorial teach things like that?  :smiley-confuse:


Arduino: Lesson 1 - Blinking an LED
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Budvar10

This is probably LED for 5V with built in resistor e.g. Kingbright L-7113ID-5V.
Arduino clone with ATmega1284P   http://forum.arduino.cc/index.php?topic=277260.0

rtek1000

This is probably LED for 5V with built in resistor e.g. Kingbright L-7113ID-5V.
Maybe, but it gets too confusing for the beginner, do not you think?
Please avoid private messages, your question may be someone's answer in the future!

Budvar10

Arduino clone with ATmega1284P   http://forum.arduino.cc/index.php?topic=277260.0

pert

This is probably LED for 5V with built in resistor e.g. Kingbright L-7113ID-5V.
No. If you watch the video, they're relying on there being a built-in resistor on pin 13. This was the case with some old Arduino boards before they realized that makes the pin not so good for uses other than blinking an LED. I'm not sure if the pre-v3 Uno used in the video had the resistor or not. Unfortunately Arduino doesn't bother to provide hardware design version history beyond a short text summary in the product page.

Regardless, I still think it was a bad idea to skip the resistor. Even if a beginner happened to have a board with the built-in LED, some will end up assuming that they can get by without resistor on all pins and damage their Arduino board. I think it was done by a kid so we have to give them some slack but it's really frustrating to see people spreading bad information.

Here's one that's much, much worse:
http://johnny-five.io/examples/


That's the first thing you see when you click on Examples on the Johnny Five website. Johnny Five is the most popular Arduino project on GitHub. They are teaching many thousands of people to use Arduino without understanding the most basic concepts. For years, they even had another one of these examples that told you to connect a plain DC motor directly to an Arduino IO pin, which was only fixed in the last few months:
http://web.archive.org/web/20180420163002/http://johnny-five.io/examples/motor/

I wonder how many destroyed Arduino boards and sad, frustrated, confused beginners that was responsible for.

rtek1000

 :o

I get sad just imagining someone doing these tutorials, without knowledge, or even to harm someone.

So people upset because your board does not work, or never worked properly, come here in the forum look for correct information, but it is already too late

:(
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pert

I was thinking the same thing. We always get stuck trying to clean up the mess left behind by all the terrible Instructables, YouTube videos, etc.

Budvar10

.. I'm not sure if the pre-v3 Uno used in the video had the resistor or not. Unfortunately Arduino doesn't bother to provide hardware design version history beyond a short text summary in the product page...
Yes, this UNO used in the video looks like R1. Versions prior R3 have LED with resistor in series between pin 13 and GND. Here is the schematics:
https://www.arduino.cc/en/uploads/Main/arduino-uno-schematic.pdf.
Pin 13 is directly on MCU's output.
Arduino clone with ATmega1284P   http://forum.arduino.cc/index.php?topic=277260.0

westfw

There hasn't been a series resistor between the avr and the pin 13 connector since WAY before any rev of Uno.  Early UNOs have a resistor and led on the board connected the the avr, and r3 UNOs have the opamp half as a driver.  But even diecimilla had gotten rid of the resistor to the pin...

On the plus side, it turns out that driving an led from an avr with a resistor usually doesn't burn out either the led or the avr, even if it isnt "good practice"

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