Strange resistorless LED sample circuit

I’ve recently acquired an arduino learning kit and while trying out sample projects I bumped into this one:

There is also this video with the circuit running: Control a LED using relay arduino

Why there is no resistor there for the led? Is it a design mistake or … ?

While implementing the project myself I added an 220 Ohm resistor. The LED’s brightness was the same as if I connected it directly to 5v (edit: without a relay).

I agree, that tutorial is wrong, there should always be a resistor in series with an LED (unless using a specialized constant current driver, typically used for 1W or higher LEDs). And in the video, the LED is blindingly bright, as you'd expect. I'm stunned it didn't instantly burn out.

Reminds me of a tutorial video of Jeremy Blum.
Seems like a clever guy, but he also uses LEDs without CL resistor (@ 5min20sec).
He assumes there is a CL resistor on pin13 (wrong).
Leo..

Wawa:
He assumes there is a CL resistor on pin13 (wrong).

If that was a really old video he would be correct.

One of the earliest Arduinos had a (bad!) wiring mistake and there really was a resistor on pin 13. :astonished:

Yes, knew that was a 'feature' on ancient boards, but not when they stopped it.

Just saw that the video was made in Jan 2011.
Should be updated for the current Uno version, to stop confusion.
Lots of people are copying bad advice from the internet.
The author of that example book might have watched this video.
Leo..

Just saw that the video was made in Jan 2011.

Then he should have known better. I think it was 2008 when the resistor last was on an Arduino board on pin 13. It was removed because it impeded the SPI interface.

Grumpy_Mike:
It was removed because it impeded the SPI interface.

It certainly did! Reference to that circuit shows that it could never output a logic HIGH and could only just serve to dimly light another LED.