Use this forum to chat about hardware specific topics for the ESP8266 (peripherals, memory, clocks, JTAG, programming)

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By sahilautotest
#88962 Hi everyone

I have a bare ESP-07S board and I have been using a USB to RS232 Serial converter cable to try and upload an Arduino sketch and it has been failing. I've linked the datasheet below of the cable I'm using ... CABLES.pdf

Link to the ESP-07S Wifi Module datasheet

The error I get is:
raise FatalError('Failed to connect to %s: %s' % (self.CHIP_NAME, last_error))
esptool.FatalError: Failed to connect to ESP8266: Timed out waiting for packet header

I have been following this tutorial below where I have 4 x 10k resistors and capacitors
in place on my breadboard. I have set GPIO15 and GPIO2 both low, while GPIO2 is set to high. I've also confirmed that I have 3.3 volts running on the module and not 5V because I know that I will fry the module of 5V is applied.

I also placed a capacitor between the EN and GND pin as mentioned in this article below but it was still failing: ... et-header/

Is the best solution just to purchase a USB to TTL converter like this one and not use a USB to RS232 converter cable:

Thank you
User avatar
By eriksl
#88984 RS232 is typically 12-18 V, positive and negative.

"TTL serial", which the ESP's are using can be anything, but are typically 5 V or 3.3 V.

And yes, it's important that they match. Most USB converters can be configured to supply either 3.3 V or 5 V, this will also determine what voltage is used for the signalling.

If you cannot use 3.3 V for whatever reason, you might (!) get away by putting some decent resistors in series with the signalling lines and hope that's enough for the internal clamping diodes in the ESP to be able to do their job without frying them. No guarantees!