So you're a Noob? Post your questions here until you graduate! Don't be shy.

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By Bram van Oosterhout
#83218 Update 8 October 2019.
Following advice received and further experimentation I have answered my own questions in post #8.
The reported voltages do no harm and the upload was affected by a power issue.
For details see post #8
Thanks for all your help

Original question
Hi there,
I have some experience with the Arduino, but this is my first attempt using the ESP8266. I purchased
Geekcreit® ESP8266 ESP01 WIFI Transceiver Wireless Module + USB To ESP8266 Serial Adapter Wireless WIFI Develoment Board from Bangood.
I purchased multiple ESP8266 ESP01 WIFI Transceiver Wireless Module and a single programmer.

I have 2 questions.
1. I measure the following voltages
on the pins of the USB To ESP8266 Serial Adapter . There are many warnings on the web that the ESP8266 does not tolerate 5V. Is the 5V on the RX GPIO3 of concern?

This module works properly when I connect TX to RX. The Serial monitor in the Arduino IDE faithfully echos all characters.

Here are the voltages:
Code: Select allPin                --------------Voltage to GND----------------
                     without    with ESP8266 plugged in
Vcc 3.3V            3.6                    3.6
RST                   0                       2.8
CH_PD/EN             3.6                     3.6
TX GPIO1              3.6                    3.6
RX GPIO3              5                       5
Flash GPIO0          2.4                    2.4
GPIO2               2.4                    3.6
GND                  0                       0

2. How to load a sketch?
I think I confuse the term "Flash" with "Loading a sketch"
I use the Arduino IDE. When I plug in USB-UARTESP8266 combo I pull GPIO0 to ground as described by Arjun SK here. Then I attempt to load the default sketch:
Code: Select allvoid setup() {
  // put your setup code here, to run once:


void loop() {
  // put your main code here, to run repeatedly:


but the upload fails with "esptool.FatalError: Failed to connect to ESP8266: Timed out waiting for packet header"

On the other hand, The wiki, in article All in one ESP-01 to USB converter suggest that GPIO0 is pulled down when you want to update the firmware. Not when you want to load a sketch.

I assume the wiki is correct. And I should be able to upload a sketch without any trickery. is that correct?

Thanks for reading this far. Looking forward to your answers.
Bram van Oosterhout
Last edited by Bram van Oosterhout on Tue Oct 08, 2019 6:01 am, edited 1 time in total.
User avatar
By mgsecord62
Bram van Oosterhout wrote:Is there anyone who can answer these questions? I am still interested.

1. The ESP8266 voltage rating is 3.6 volts max. The 5 volts on GPIO3 is a big concern. Hopefully the ESP8266 chip has not been damaged.
2. You need to apply power when GPIO0 is grounded to put the device in the download mode or if GPIO0 is grounded after power is applied you can momentarily connect RST to ground to restart in the download mode. Then you should be able to load the sketch.