Communication between two ESP32, USART vs RS232 with MAX3232

Question

I have two ESP32 that are communicating via USART (TTL) on the Serial2.

The TX2 pin of ESP_Alice is connected with the RX2 pin of ESP_bob.

The RX2 pin of ESP_Alice is connected with the TX2 pin of ESP_bob.

(left on the image)

It works, but it's a noisy channel and I need to increase cable length. I bought two MAX3232-based boards and I connected them as in the right scheme on the image:

TX2 RX2 between ESP and MAX3232 boards are connected directly (on the TTL SIDE), the TX and RX pin of the two boards (on the RS232 side) are crossed.

Boards are powered with 3.3 V and GND pin connected to ESP_Alice

It does not communicate at all (same program that works correctly when the two boards are connected directly with the TTL USART).

ESP32 connections

Connections of RS232 to TTL boards

What am I doing wrong here?

• dda: On the right side, 3.3v and GND, and GND on the second board, are connected to the wrong pins.
• Edan Lee: try to esp tx <--> rx max3232 And esp rx <--> tx max3232
• the busybee: @EdanLee Look at the arrows on the PCB: TXD of the MAX3232 boards is an input, so connecting ESP's TX here is correct.

Answer 1

You seem to have the polarity of the supply to the RS232-TTL boards reversed.

There is a + symbol next to the pads that you have the GND connected to.

It should be like this:

Corrected supply polarity

• Carlo Tavian: Sorry, I messed up with the second image that I meant to use as an 'enlargement' of the first one. The wiring is already connected as you suggest in your image. I'll try to update my question with your image