user81916: I know the whole controlling a fan with an arduino thing is getting old, but somehow I still don't get it to work. Tried to answer it based on other questions but I am too much of a newbie to extrapolate the info there to my specific problem.
For my project of building an arduino-controlled mushroom grow box, I need to control a PC fan and ultrasonic fogger. I chose these two products:
DC 3-12V Ultrasonic Fogger,
DC 5V Fan
I hoped that by using 5V devices, I could connect them to the 5V pin of the arduino to power them. However, with the whole setup (see circuit and photo), they don't run. I'm using a BC337 transistor. I tried them both separately, but nothing.

I know that there is a resistor missing in the photo, I forgot to put it back in when I took it.

The fan works if I just insert it between 5V and GND but the fogger doesn't do anything.
The code works (and is fairly hard to mess up) but I'm including it anyway.
const int fan = 3;

void setup() {
  pinMode(fan, OUTPUT);
}

void loop() {
  digitalWrite(fan, HIGH);
}

Do I need a higher voltage power supply or is something wrong with my transistor choice? Which parts would be a better fit? Or am I entirely on the wrong track?
In the end the full thing should also contain an LCD display and a SCD41 sensor, both connected via I2C.

Thanks in advance!

user42015: About the ultrasonic fogger:
The product description is misleading. This is a pure transducer. That means it does not generate its own ultrasonic frequency and is thus not DC. You need to provide an AC voltage at the frequency of 113kHz (though one reviewer states to have received products with a resonance frequency of 108kHz. Maybe just try out what you have). You can use utilize Timer1 to generate a fitting square wave at one of its output compare pins.
Note: Since you are more at the lower end of the foggers voltage rating you might see a bad performance when you get it to work. For it to work with its full power you should probably drive it with 12V, utilizing its full range.
About the fan:
As jsotola already stated in the comments, the red wire of the fan is not connected to the circuit. If you look at your breadboard you will see that the blue and red lines are interrupted in the middle of the breadboard. This means, that the rails are disconnected here (divided into the left and the right part of the breadboard). Move the red fan cable to the left of the red LED jumper wire. Then you should be connected.

81916: <p>I know the whole controlling a fan with an arduino thing is getting old, but somehow I still don't get it to work. Tried to answer it based on other questions but I am too much of a newbie to extrapolate the info there to my specific problem.</p>
<p>For my project of building an arduino-controlled mushroom grow box, I need to control a PC fan and ultrasonic fogger. I chose these two products:</p>
<p><a href="https://www.amazon.de/gp/product/B07V72T1T9/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&amp;psc=1" rel="nofollow noreferrer">DC 3-12V Ultrasonic Fogger</a>,
<a href="https://www.amazon.de/gp/product/B07X93XGBD/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&amp;psc=1" rel="nofollow noreferrer">DC 5V Fan</a></p>
<p>I hoped that by using 5V devices, I could connect them to the 5V pin of the arduino to power them. However, with the whole setup (see circuit and photo), they don't run. I'm using a BC337 transistor. I tried them both separately, but nothing.</p>
<p><a href="https://i.stack.imgur.com/z19Rm.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/z19Rm.jpg" alt="Circuit of the fan connected to arduino. Fogger was hooked up the same way" /></a></p>
<p>I know that there is a resistor missing in the photo, I forgot to put it back in when I took it.</p>
<p><a href="https://i.stack.imgur.com/qUO6i.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qUO6i.jpg" alt="How it actually looked - but missing a resistor which I forgot to add in this (Refer to circuit)" /></a></p>
<p>The fan works if I just insert it between 5V and GND but the fogger doesn't do anything.</p>
<p>The code works (and is fairly hard to mess up) but I'm including it anyway.</p>
<pre><code>const int fan = 3;

void setup() {
  pinMode(fan, OUTPUT);
}

void loop() {
  digitalWrite(fan, HIGH);
}
</code></pre>
<p><strong>Do I need a higher voltage power supply or is something wrong with my transistor choice? Which parts would be a better fit? Or am I entirely on the wrong track?</strong></p>
<p>In the end the full thing should also contain an LCD display and a SCD41 sensor, both connected via I2C.</p>
<p><a href="https://i.stack.imgur.com/gEGh4.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gEGh4.jpg" alt="enter image description here" /></a></p>
<p>Thanks in advance!</p>
 42015: <p><strong>About the ultrasonic fogger:</strong></p>
<p>The product description is misleading. This is a pure transducer. That means it does <strong>not</strong> generate its own ultrasonic frequency and is thus not DC. You need to provide an AC voltage at the frequency of 113kHz (though one reviewer states to have received products with a resonance frequency of 108kHz. Maybe just try out what you have). You can use utilize Timer1 to generate a fitting square wave at one of its output compare pins.</p>
<p>Note: Since you are more at the lower end of the foggers voltage rating you might see a bad performance when you get it to work. For it to work with its full power you should probably drive it with 12V, utilizing its full range.</p>
<p><strong>About the fan:</strong></p>
<p>As jsotola already stated in the comments, the red wire of the fan is not connected to the circuit. If you look at your breadboard you will see that the blue and red lines are interrupted in the middle of the breadboard. This means, that the rails are disconnected here (divided into the left and the right part of the breadboard). Move the red fan cable to the left of the red LED jumper wire. Then you should be connected.</p>
