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I would like to connect Arduino UNO and ESP 01 module. I use Arduino IDE and I tried to test comunication via serial monitor, I get "ready" message from ESP 01, but I am not able to issue AT command from serial monitor. It only inserts random characters to console. It seems that no new line character is issued, because if I try to insert mode commands, they are inserted next to previous characters. I use "Both NL & CR" and 115200 baud settings in Arduino IDE. Tried also 9600 baud, but then text is unreadable.

I used folowing 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 screenshot of Serial monitor: enter image description here

EDIT: PROBLEM RESOLVED:

My arduino is connected to PC via usb, so I changed pins for communication with ESP by SoftwareSerial to pins 10 and 11. Now it works. Thank you.

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It could be the case, that the Arduino power supply is insufficient.

"[...] note that the Arduino 3.3V regulated output (50 mA max) can't drive the current requested by the ESP (Up to 200 mA). Some tutorials on the Internet use the Arduino 3.3V to power the ESP, but it didn't worked for me. I'm using an external power supply (An old 5V Android charger)."Source

Possible, that the power consumption was within range when the readable text was printed and too high when all the unreadable stuff was sent.

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Tried to use power supply with 3,3V / up to 1A and now and received only random characters instead of "ready"message :( – Petr Jul 10 at 12:41
    
Also, I inserted power source directly to Vcc pin of ESP, didnt uset any kind of diode/stabilizator etc, this could problem maybe? – Petr Jul 10 at 13:03
    
Also, my voltage divider is: 3300 Ohm and 6600 Ohm, not sure if this is ok :x – Petr Jul 10 at 13:21

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