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By JoeSl
#84037 Hello everyone!

This must be a question that is asked a million times on this forum..!
I'm connecting an arduino uno rev3 to a Esp8266-01s module.

I'm following these setups: ... duino-uno/
The arduino is in reset mode and i'm using the arduino ide serial monitor to send commands.

If I don't use a voltage divider, it works. I can send commands and replies are sent (115200 baud, NL+CR). But I was afraid this would damage it in the long run?
If I use a voltage divider with three 1k resistors, when I power the board the TX blue led stays on and nothing happens. The circuit is:

Code: Select allARDUINO_TX -> 1k ----> 1k -> 1k -> GND
                   '-> MODULE_RX     

Could anyone please help out? what is going on?

Thanks a lot!
User avatar
By btidey
#84053 The problem here is that the UNO has a USB to Serial converter on board already connected to the TX and RX pins of the UNO microcontroller. That means both the ESP TX and the UNO microcontroller are trying to drive the RX lines. It might sort of work if one can overdrive the other but it is not a good solution.

Do yourself a favour and get a real standalone USB serial converter rather than trying to use the UNO. They are very cheap.
User avatar
By JoeSl
#84054 Thanks for your reply! I am aware of this but as long as you don't use them at the same time, it shouldn't really be a problem, isn't it? I am able to use the ESP module with my PC (serial monitor) or with the UNO.

My question is solely about the voltage to drive the ArduinoTX->EspRX: works at 5V but doesn't at 3.3V using a 1k+1k+1k voltage divider.