On the ESP side, I have connected IO0 and IO15 to GND through pulldown resistors and CHIP_EN to VCC through a pullup resistor. 3.3V and GND are connected to an external regulated 3.3V power supply, and TX/RX are connected to my arduino uno TX/RX through a logic-level-converter. I have also tried directly connecting the ESP TX and connecting the ESP RX through a voltage divider, this does not seem to make a difference.
On the arduino uno side, in addition to the TX/RX, the atmega chip is removed and the device is connected to USB.
When I try to upload the blink sketch (with Generic esp8266 selected as the board with settings shown here.
When I try to upload the sketch (CTRL+U), I get the following messages:
Sketch uses 202,100 bytes (46%) of program storage space. Maximum is 434,160 bytes.
Global variables use 32,982 bytes (40%) of dynamic memory, leaving 48,938 bytes for local variables. Maximum is 81,920 bytes.
warning: espcomm_sync failed
error: espcomm_open failed
I notice that the RX LED (transmitting from arduino) on the arduino flashes regularly but the TX LED (receiving) never lights up.
Additionally, if I boot the ESP with IO0 pulled high instead of low (regular boot instead of boot into flash mode), the existing sketch on the device runs perfectly. I cannot seem to re-upload a new sketch and cannot figure out what I am doing wrong.
Can anyone see any obvious mistake I am making?