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I connected my esp8266 with USB to TTL CP2102 as follows:

USB to TTL      ESP
----------------------------------------------------
RX              TX
TX              RX(10K ohm resistor in between them)
GND             GND
3.3V            VCC, CH_PD,GPIO0,Reset

then I connected it with my laptop and opened arduino IDE. Why isn't responding to my AT command in serial monitor?

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  • \$\begingroup\$ If you are using the ESP8266 with the AT command set and talking to it directly from a PC, your question doesn't concern Arduino, should not be tagged arduino-uno, and is off-topic here. \$\endgroup\$ – Chris Stratton May 21 '16 at 22:24
  • \$\begingroup\$ See sparkfun.com/datasheets/IC/cp2102.pdf page 13... the 3.3V from the CP2102 probably are too weak to supply the ESP8266. \$\endgroup\$ – gone May 22 '16 at 8:13
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You're not giving a lot of details. My first guess is you don't have the AT firmware loaded :)

But:

  • Which ESP module are you using?
  • Are you sure the AT firmware is (pre)loaded/flashed?
  • Does any blinking occur on anything when the module powers on? A ESP always sends some data over serial on bootup, and most CP2102 modules have leds for TX/RX, do they blink?
  • Did you actually install the CP2102 driver, does it show up as a COM port in windows?
  • I don't think it's an issue, but why is the 10k resistor there? You could try without it, but I'd also like to know why for my own projects (I normally don't use it) :)
  • I'm behind a proxy, so can't look it up, but make sure all the pins are held high/low correctly, you seem to have everything on 3v3, isn't there usually some that need to go to GND? Can't remember..
  • Like someone suggested already, CP2102 might not provide enough power, so try a dedicated 3.3v power source. My personal experience is that it is enough as long as WIFI stays off though.
  • Triple check all your wiring :)
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