Arduino to ESP connection problem

Hello,

I have a ESP 8266 development kit. I have updated AT firmware over it and check using max 3232 module. AT commands working fine over that but when i connect arduino in stand of max 3232 converter that was not working at all. My connection is as below. I use external power source to give 3.3 V power to esp board.

connection:

ESP - Arduino

gnd - gnd
TX - Rxd( pin 19 of arduino mega)
Rx - Txd(pin 18 of mega) (voltage divider ckt is between thr ,20k and 10k resisitor divider to convert arduino 5v to 3.3V to rx pin esp)
3.3V - VCC esp board ( using external power source adjustable)
Arduino is connected to USB of my computer.

I have below board of esp.
http://www.esp8266.com/wiki/doku.php?id=esp8266-dev-boards

Please post the sketch you’re using to test communication with the ESP8266. Use code tags(</> button on the toolbar).