user77997: Hello. I've got a question about DHT11 sensor. Why should pullup resistor be connected as on the image below:

while as far as I know, pullup resistor should be placed between Arduino 5V pin and Vcc of sensor as shown here:

PS: I know that there is a wrong icon of DHT11, but I couldn't find a correct one.

user4143: You require a pullup resistor between the data wire and VCC because the DHT11 uses a bidirectional communication system on a single wire.  When neither end is communicating both ends of the link will be in "high impedance" mode - i.e., input mode. In that case the signal will be "floating" and needs the pullup to keep it in a known state.
When actively communicating the outputs switch to "open drain" mode to allow then to pull the signal low against the pull of the pullup resistor.
A resistor in series with the Arduino's 5V and the VCC of the DHT11 is not a pullup resistor. It is not an arrangement that you would ever want, since it would make the voltage to the DHT11 unstable.

77997: <p><strong>Hello. I've got a question about DHT11 sensor. Why should pullup resistor be connected as on the image below:</strong>
<a href="https://i.stack.imgur.com/7iDG3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/7iDG3.png" alt="enter image description here" /></a></p>
<p><strong>while as far as I know, pullup resistor should be placed between Arduino 5V pin and Vcc of sensor as shown here:</strong>
<a href="https://i.stack.imgur.com/RrSgf.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/RrSgf.png" alt="enter image description here" /></a></p>
<p><strong>PS: I know that there is a wrong icon of DHT11, but I couldn't find a correct one.</strong></p>
 4143: <p>You require a pullup resistor between the data wire and VCC because the DHT11 uses a bidirectional communication system on a single wire.  When neither end is communicating both ends of the link will be in &quot;high impedance&quot; mode - i.e., input mode. In that case the signal will be &quot;floating&quot; and needs the pullup to keep it in a known state.</p>
<p>When actively communicating the outputs switch to &quot;open drain&quot; mode to allow then to pull the signal low against the pull of the pullup resistor.</p>
<p>A resistor in series with the Arduino's 5V and the VCC of the DHT11 is <em>not</em> a pullup resistor. It is not an arrangement that you would ever want, since it would make the voltage to the DHT11 unstable.</p>
