Using a second Serial Port

On the ESP32 UART0 is normally reserved for interactive use with REPL. Sometimes we need a UART to communicate with external devices. Typical examples are:

  • fingerprint readers using a serial communication protocol
  • GPS modules
The ESP32 has 3 UARTs of which however UART1 is reserved for use with flash memory. However UART2 is free.

Connect the USB to Serial adapter to the ESP32 as shown in the table below

USB to Serial Adapter ESP32 pins
Rx GPIO 17
Tx GPIO 16
Gnd Gnd
As a first quick test we can try to write "Hello World to UART2 to which we connect a minicom virtual terminal.

thonny is connected to UART0 on /dev/ttvUSB0 (connect this first). minicom is connected to UART2 on /dev/ttyUSB1. Start minicom with:

minicom -D /dev/ttyUSB1

Here is the screen dump of the REPL session

uart2.png

And this is what we see on minicom:

uart2-minicom.png

... if you are too lazy to type, here is the corresponding script:

https://iotworkshop.africa/pub/IoT_Course_English/SerialPorts/uart.py.txt

-- Uli Raich - 2020-05-09

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PNGpng uart2-minicom.png r1 manage 23.7 K 2020-05-09 - 19:57 UliRaich  
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