Arduino does not read data from NODEMCU

Other Hardware 3rd Party Boards
1

Arduino (ARD) does not read data from NODEMCU (NDU)

I want the Arduino to exchange data with a UDP / TCP server. I connected the ARD to the NDU via a serial port (ARD TX - RX NDU, ARD RX - TX NDU), I connected the Transmit line from the Arduino via a voltage divider to the receiving line of the NDU. In Arduino, I uploaded a terminal emulation program. I use SoftwareSerial to communicate with NDU. The Arduino does not receive data from the NDU. I tested the same program with MEGA 2560 and the result is the same - wrong. NDU modul is powerd by external power supply.

That's why I connected the Arduino to a USB Serial TTL adapter. This combination works perfectly. I also connected the NDU to a USB serial TTL port. And this combination works flawlessly.

When I connect ARD to NDU and enter an empty program in ARD, then the ARD Serial Monitor exchanges data with the NDU module.

When ARD is connected to MDU I have proved that NDU receives correct data from ARD. The TX line of the NDU, which is connected to the RX line of the ARD, I connected in parallel with a special USB TTL adapter. I found that the MDU was sending correct responses to commands from the Arduino. I send AT commands to the NDU module. I don't know why the Arduino can't read data from the NDU module.

I searched this forum and did not encounter a similar problem. Any idea, suggestion is welcome, Thank you.

2

I have solved the problem and I want to share the solution with you. It will probably be useful to some of you. The solution to the problem is unusual and has only confirmed the definition of theory and practice. The theory is when everything is clear to you, but your device does not work (my case). The practice is when your device works but you don't know why (my case),

I solved the problem when I removed the voltage divider and connected the transmit line from the Arduino directly to the NODEMCU receiving line (although this is not recommended). Let me remind you that the problem was not on the receiving side of NODEMC but on the receiving side of Arduino.

Although I have solved the problem, I have no explanation for the solution. If any of you know the explanation it would be good to share it with us.

3

I'm glad you solved your problem.

Difficult to comment without seeing your setup, but my best guess would be using breadboard and loose wires, removing the divider moved a badly connected wire and improved the connection.

If you want a better answer please post a schematic and some photos of what you have.

Thanks,