user88178: I'm still quite new to electronics, so please forgive me if the answer is obvious.
I was wondering why virtually all the example circuits I find use the 5V power supply with resistors for all the components instead of the 3V3 power supply directly.
Even for the most simplistic "Blink" example, they use 5V pin and a 220 Ohm resistor to protect the LED instead of using the built-in 3.3V pin.
Yes, I know that in former times "everything" ran on 5V, but since we already have a lower voltage built-in, why not use it and reduce the number of components needed?
TIA for anyone who can solve this puzzle for me.
mav

user10794: First, even with 3.3V, an LED needs a resistor to limit the current through it. So, running with 3.3V doesn't solve that particular problem. Try Googling for "LED current limiting resistor".
Second, many Arduinos are designed to run using 5V. In many cases they have an input power jack which can accept a range of voltages and use a voltage regulator to convert it down to 5V,
Why not convert down to 3.3V you might ask? Well, the higher the voltage, the faster the processor can run, within its design limits. For example, the Atmega328P (which is in the Arduino Uno, and others) could only run at 13 MHz at 3.3V rather than 16 MHz.

... instead of using the built-in 3.3V pin

But that pin is only provided for convenience. You can't turn it on or off by a program.
The higher voltage (5V vs 3.3V) can be more convenient in some situations, for example switching motors on and off, or with other devices designed to work with 5V.
Motors or other high-power devices are typically turned on with MOSFET transistors. To be efficient, they need to fully turn on (have a low resistance between Source and Drain) and even so-called "logic level" MOSFETs typically require 5V to fully turn them on, rather than 3.3V. If you tried to control a motor with a 3.3V based board you would probably need extra components to turn the MOSFET on properly, so lowering the voltage could potentially add components, not reduce them.
On the other hand, many components these days are designed to work with 3.3V (or lower) so the choice of 5V is a bit of a compromise.

88178: <p>I'm still quite new to electronics, so please forgive me if the answer is obvious.</p>
<p>I was wondering why virtually all the example circuits I find use the 5V power supply with resistors for all the components instead of the 3V3 power supply directly.</p>
<p>Even for the most simplistic &quot;Blink&quot; example, they use 5V pin and a 220 Ohm resistor to protect the LED instead of using the built-in 3.3V pin.</p>
<p>Yes, I know that in former times &quot;everything&quot; ran on 5V, but since we already have a lower voltage built-in, why not use it and reduce the number of components needed?</p>
<p>TIA for anyone who can solve this puzzle for me.<br />
mav</p>
 10794: <p>First, even with 3.3V, an LED needs a resistor to limit the current through it. So, running with 3.3V doesn't solve that particular problem. Try Googling for &quot;LED current limiting resistor&quot;.</p>
<p>Second, many Arduinos are designed to run using 5V. In many cases they have an input power jack which can accept a range of voltages and use a voltage regulator to convert it down to 5V,</p>
<p>Why not convert down to 3.3V you might ask? Well, the higher the voltage, the faster the processor can run, within its design limits. For example, the Atmega328P (which is in the Arduino Uno, and others) could only run at 13 MHz at 3.3V rather than 16 MHz.</p>
<blockquote>
<p>... instead of using the built-in 3.3V pin</p>
</blockquote>
<p>But that pin is only provided for convenience. You can't turn it on or off by a program.</p>
<p>The higher voltage (5V vs 3.3V) can be more convenient in some situations, for example switching motors on and off, or with other devices designed to work with 5V.</p>
<p>Motors or other high-power devices are typically turned on with MOSFET transistors. To be efficient, they need to fully turn on (have a low resistance between Source and Drain) and even so-called &quot;logic level&quot; MOSFETs typically require 5V to fully turn them on, rather than 3.3V. If you tried to control a motor with a 3.3V based board you would probably need extra components to turn the MOSFET on properly, so lowering the voltage could potentially add components, not reduce them.</p>
<p>On the other hand, many components these days are designed to work with 3.3V (or lower) so the choice of 5V is a bit of a compromise.</p>
