user69051: How too know whether digitalwrite(HIGH, pin_number) sets the voltage to 5 volts or 3.3 volts. I am yet to purchase arduino uno. I want digital pin voltage to be 5 volts. I am aware that thereis a pin already have 5 volts but I want to know only about the voltage output at digital pins.
Sorry if question is too silly. I am not very knowledgable in Electronics.

user4143: Different boards operate internally at different voltages. This is dictated by the main chip on the board.  That main internal operating voltage is also the voltage at which the IO pins operate.
Most "old" Arduino boards operate at 5V.  This includes, but is not limited to:

Arduino UNO
Arduino Mini
Arduino Leonardo

Newer more powerful boards, many made by other companies, operate at 3.3V. Again, this includes such boards as:

Arduino DUE
Arduino MKR1000
Teensy boards (v3.0+)
chipKIT boards
ESP8266 & ESP32 boards

Some boards come in variants that give either voltage - the most notable being the Pro Mini boards from Sparkfun.  These come in both 5V and 3.3V variants and it is important to pick the right board for your needs.
In general, though:

If it's 8-bit and runs on an ATMega chip it's likely 5V unless otherwise stated
All 32-bit boards will be 3.3V unless otherwise stated.


69051: <p>How too know whether digitalwrite(HIGH, pin_number) sets the voltage to 5 volts or 3.3 volts. I am yet to purchase arduino uno. I want digital pin voltage to be 5 volts. I am aware that thereis a pin already have 5 volts but I want to know only about the voltage output at digital pins.</p>
<p>Sorry if question is too silly. I am not very knowledgable in Electronics.</p>
 4143: <p>Different boards operate internally at different voltages. This is dictated by the main chip on the board.  That main internal operating voltage is also the voltage at which the IO pins operate.</p>
<p>Most &quot;old&quot; Arduino boards operate at 5V.  This includes, but is not limited to:</p>
<ul>
<li>Arduino UNO</li>
<li>Arduino Mini</li>
<li>Arduino Leonardo</li>
</ul>
<p>Newer more powerful boards, many made by other companies, operate at 3.3V. Again, this includes such boards as:</p>
<ul>
<li>Arduino DUE</li>
<li>Arduino MKR1000</li>
<li>Teensy boards (v3.0+)</li>
<li>chipKIT boards</li>
<li>ESP8266 &amp; ESP32 boards</li>
</ul>
<p>Some boards come in variants that give either voltage - the most notable being the Pro Mini boards from Sparkfun.  These come in both 5V and 3.3V variants and it is important to pick the right board for your needs.</p>
<p>In general, though:</p>
<ul>
<li>If it's 8-bit and runs on an ATMega chip it's likely 5V unless otherwise stated</li>
<li>All 32-bit boards will be 3.3V unless otherwise stated.</li>
</ul>
