ESP32 UART to Raspberry Pi I2C

Question

I am trying to understand how to connect an ESP32's UART pins to my raspberry pi 3B+'s I2C pins. I see several bridge chips available for this like TI's MSP430 Datasheet. But I am not very circuit savvy so I am having a difficult time. The pins I need to use on the ESP32 are: GPIO 9 and 10, RX and TX respectively (UART1). On the Raspberry Pi: GPIO 2 and 3, SDA and SCL respectively. Does anyone know answers to the questions below?

1. Besides connecting the RPi, ESP, Vcc, GND pins to the bridge at the correct I/O positions on the chip, what additional circuitry would be needed to make good communication?

2. What the ESP32 code would look like (Arduino IDE)?

3. What the Pi's code would look like (python)?

Answer 1

^{simulate this circuit – Schematic created using CircuitLab}

The ESP32 has more than 1 UART. Although it is common to only use one of them in the default configuration, the ESP32 has 3 UARTs. You can configure which GPIO pins to use by using the uart_set_pin() function. You should check the datasheet or the Espressif website for the details.

Using multiple UARTs allows the ESP to act as a Serial Bridge. This function is frequently implemented with the different flavors of ESPs as a WiFi Serial Bridge, but it works for wired connections as well.

UART Page

Answer 2

A others have commented, the easiest way to communicate between the ESP32 and RPi is using asynchronous serial; if you don't have a spare serial port on the Pi, you can add a USB-to-serial adaptor.

If you choose one with an FTDI chip, then just plug it in to the Pi and you get another serial port; the other common type of adaptor uses the CP2102 chip, and I think this might require you to install a driver on the Pi, but you'll find plenty of instructions how to do this on the Web, e.g. this page

Make sure that you are using an adaptor with the correct voltage level (3.3V logic signals, not 5V or RS232 voltages), then connect the ground wires together, and Tx on Pi to Rx on ESP32, Rx on Pi to Tx on ESP32.

With regard to how you use this link to communicate, any character you send on one side will just appear at the other. However, it is prudent to create a simple communication format, such as a command letter, maybe some numeric values, then a Carriage Return to signal the end of the command line. This has 2 benefits; it means you can use a serial terminal to enter commands manually, and also it avoids the possible confusion where the recipient tries to take action when it has only received part of a command.