user23739: I would like to connect an Arduino Uno and an ESP 01 module. I use the Arduino IDE and I tried to test communication via serial monitor. I get the "ready" message from the ESP 01, but I am not able to issue AT commands from the serial monitor. It only displays random characters on the console. 
It seems that no newline character is issued, because if I try to insert commands, they are inserted next to previous characters. I use "Both NL & CR" and 115200 baud settings in Arduino IDE. I tried 9600 baud too, but then the text is unreadable.
I used the following pins on my ESP-01:
Vcc -> 3,3V
Gnd -> Gnd
Rx  -> Tx(pin 0) of my Arduino, used voltage divider to make it 3.3V.
Tx  -> Rx(pin 1) of Arduino
CH_PD -> 3.3V

Please see serial monitor screenshot:

EDIT: PROBLEM RESOLVED:
My Arduino is connected to my PC via USB, so I changed pins for communication with the ESP by SoftwareSerial to pins 10 and 11. Now it works. Thank you.

user653: Just to have an answer instead of just an edit/addition to the question:

EDIT: PROBLEM RESOLVED:
My Arduino is connected to my PC via USB, so I changed pins for communication with the ESP by SoftwareSerial to pins 10 and 11. Now it works. Thank you.

Ok... sure... your Uno's Atmega384 was talking with pins 0 and 1 to the USB adaper chip (Atmega16u2 on Uno R3) and at the same time to the ESP-01.
Read the fine schematic: Arduino Uno R3

23739: <p>I would like to connect an Arduino Uno and an ESP 01 module. I use the Arduino IDE and I tried to test communication via serial monitor. I get the "ready" message from the ESP 01, but I am not able to issue AT commands from the serial monitor. It only displays random characters on the console. </p>

<p>It seems that no newline character is issued, because if I try to insert commands, they are inserted next to previous characters. I use "Both NL &amp; CR" and 115200 baud settings in Arduino IDE. I tried 9600 baud too, but then the text is unreadable.</p>

<p>I used the following pins on my ESP-01:</p>

<pre><code>Vcc -&gt; 3,3V
Gnd -&gt; Gnd
Rx  -&gt; Tx(pin 0) of my Arduino, used voltage divider to make it 3.3V.
Tx  -&gt; Rx(pin 1) of Arduino
CH_PD -&gt; 3.3V
</code></pre>

<p>Please see serial monitor screenshot:
<a href="https://i.stack.imgur.com/boUq7.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/boUq7.jpg" alt="enter image description here"></a></p>

<p><strong>EDIT: PROBLEM RESOLVED:</strong></p>

<p>My Arduino is connected to my PC via USB, so I changed pins for communication with the ESP by SoftwareSerial to pins 10 and 11. Now it works. Thank you.</p>
 653: <p>Just to have an answer instead of just an edit/addition to the question:</p>

<blockquote>
  <p>EDIT: PROBLEM RESOLVED:</p>
  
  <p>My Arduino is connected to my PC via USB, so I changed pins for communication with the ESP by SoftwareSerial to pins 10 and 11. Now it works. Thank you.</p>
</blockquote>

<p>Ok... sure... your Uno's Atmega384 was talking with pins 0 and 1 to the USB adaper chip (Atmega16u2 on Uno R3) and at the same time to the ESP-01.</p>

<p>Read the fine schematic: <a href="https://www.arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf" rel="nofollow noreferrer">Arduino Uno R3</a></p>
