Help writing a component to read UART data

[Tmp2k (Steven Tomlinson)]

Hi, I’m an experienced dev, but new to ESPHome and rusty on C++

I have a UHF RFID reader that just outputs a series of bytes via UART on successful read. I’ve go this working using the generic UART bus with a debug call.

I’d like to create a custom component that listens for UART, then on a delimiter e.g. 0x00 (or possibly a 100ms timeout) takes the buffer (which will contain the last read card ID as a list of bytes). Then publishes this as a hex string to a given MQTT topic, as a JSON string with some other stuff.

I want to be able to configure it with the following:

optional UART bus ID - If none configured then just default to UART bus
mqtt topic - the topic to publish the data to
device-name - can this be gotten from somewhere?

example:

uhf-rfid:
  topic: example/rfid/read

This would publish {"device":"my-card-reader","card":"23-23-64-62-14"}

I made a start here → GitHub - NemiahUK/esphome-uhf-rfid but it’s just based on the very limited example in the docs. Any help would be massively appreciated.

Thanks!

[tom_l]

@Tmp2k

I’d like to create a custom component that listens for UART, then on a delimiter e.g. 0x00 (or possibly a 100ms timeout) takes the buffer (which will contain the last read card ID as a list of bytes). Then publishes this as a hex string to a given MQTT topic,

Your component should do the UART RX only. The mqtt publish part should be done using existing ESPHome components and automations.

See: MQTT Client Component — ESPHome

[Mahko_Mahko]

You can probably do this without a component if you want.

[How to] UART read without custom component

The UART Bus component provides a write action but no read actions. Typically the UART read is implemented in a custom component that also does the processing. The UART debug sequence can be exploited to act like a call back function whenever there is received data to process. So basically instead of creating a small custom component a large lambda call can be used in the UART debug yaml. This is shared to hopefully help make implementing UART devices a bit easier for average users. It seems t…

[How to] UART read without custom component

Just providing this little example. uart: id: uart_bus tx_pin: GPIO21 rx_pin: GPIO20 baud_rate: 9600 debug: direction: BOTH dummy_receiver: true after: # bytes: 9 # timeout: 10ms delimiter: [0x7E] #Specific end byte sequence: - lambda: |- UARTDebug::log_int(direction, bytes, ','); // Log the message as int. UARTDebug::log_hex(direction, bytes, ','); // Log the message in hex. …

@Tmp2k

device-name - can this be gotten from somewhere?

There is a way which I can’t seem to find right now. But substitutions might do the job.

Edit: have a read of this thread.

How to printf device name?

Use App.get_name().c_str() for WHATGOESHERE.

[Tmp2k (Steven Tomlinson)]

Good point, I’m using this methodology elsewhere.

So I need the component to have an event like on_tag that passes the card ID as x then use lamda to do the rest e.g.

uhf_rfid:
  on_tag:
    then:
      - mqtt.publish:
          topic: ${namespace}/rfid/read
          payload: !lambda return "{\"device\":\"${device_name}\",\"tag\":\""+x+"\"}";

[Tmp2k (Steven Tomlinson)]

Thanks for the info. I’m currently using the UART debug and a lambda call but the delimiter option just doesn’t seem to work properly.

The UART device returns a fixed number of bytes per read, each one is separated by a few 100ms and they contain the same start and end bytes.

I’ve tried setting the delimiter to time based, a specific byte and a fixed length, however it seems to wait until an arbitrary amount of data is in the buffer then dumps it all in one go.

uart:
  tx_pin: 14
  rx_pin: 13
  baud_rate: 9600
  debug:
    direction: RX
    dummy_receiver: true
    after:
      delimiter: [0x00]
    sequence:
      - lambda:
          UARTDebug::log_hex(direction, bytes, ' ');
          id(mqtt_client).publish("${namespace}/rfid/read", "{\"device\":\"${device_name}\",\"tag\":\""+format_hex(bytes)+"\"}");
      - lock.unlock: door_lock

That’s what I have now, but it just returns around 3-4 tag reads with the last one truncated.