Custom UART Text Sensor

Lots of devices communicate using the UART protocol. If you want to read lines from uart to a Text Sensor you can do so using this code example.

With this you can use automations or lambda to set switch or sensor states.

#include "esphome.h"

class UartReadLineSensor : public Component, public UARTDevice, public TextSensor {
 public:
  UartReadLineSensor(UARTComponent *parent) : UARTDevice(parent) {}

  void setup() override {
    // nothing to do here
  }

  int readline(int readch, char *buffer, int len)
  {
    static int pos = 0;
    int rpos;

    if (readch > 0) {
      switch (readch) {
        case '\n': // Ignore new-lines
          break;
        case '\r': // Return on CR
          rpos = pos;
          pos = 0;  // Reset position index ready for next time
          return rpos;
        default:
          if (pos < len-1) {
            buffer[pos++] = readch;
            buffer[pos] = 0;
          }
      }
    }
    // No end of line has been found, so return -1.
    return -1;
  }

  void loop() override {
    const int max_line_length = 80;
    static char buffer[max_line_length];
    if (available() && readline(read(), buffer, max_line_length) > 0) {
      publish_state(buffer);
    }
  }
};

(Store this file in your configuration directory, for example uart_read_line_sensor.h)

And in YAML:

# Example configuration entry
esphome:
  includes:
    - uart_read_line_sensor.h

logger:
  level: VERBOSE #makes uart stream available in esphome logstream
  baud_rate: 0 #disable logging over uart

uart:
  id: uart_bus
  tx_pin: D0
  rx_pin: D1
  baud_rate: 9600

text_sensor:
- platform: custom
  lambda: |-
    auto my_custom_sensor = new UartReadLineSensor(id(uart_bus));
    App.register_component(my_custom_sensor);
    return {my_custom_sensor};
  text_sensors:
    id: "uart_readline"

Example usage

Here is an example switch using the uart text sensor to set switch state.

Here we use interval to request status from the device. The reponse will be stored in uart text sensor. Then the switch uses the text sensor state to set its own state.

switch:
  - platform: template
    name: "Switch"
    lambda: |-
      if (id(uart_readline).state == "*POW=ON#") {
        return true;
      } else if(id(uart_readline).state == "*POW=OFF#") {
        return false;
      } else {
        return {};
      }
    turn_on_action:
      - uart.write: "\r*pow=on#\r"
    turn_off_action:
      - uart.write: "\r*pow=off#\r"

interval:
  - interval: 10s
    then:
      - uart.write: "\r*pow=?#\r"