Parsing Multiple Data Segments on Bluetooth Using readStringUntil

Projects General Guidance
1

I've an App Inventor app that sends small packets of data to my ESP32 in the following format:

d12|1

Where "d12" is the data identifier, "|" is a delimiter and "1", in this case is the data. In all cases, the data being received is an integer.

This is my code:

/Bluetooth read data from phone
  if (espBT.available()) //check if data is available in the buffer
    {
      //set incoming variable to data sent from
      incoming = espBT.readStringUntil('|'); //get the button descriptor
      String button = String(incoming);
      incoming = espBT.readStringUntil('\n'); //get the associated button payload
      String butvalue = String(incoming);

      //debug
      Serial.println("button: " + button + " value: " + butvalue);

      //Parse received data
      if (button.equals(String("d10"))) { d10 = butvalue.toInt(); } //App button volume
      if (button.equals(String("d11"))) { d11 = butvalue.toInt(); } //App rotate anticlockise 90 degrees (fast)
      if (button.equals(String("d12"))) { d12 = butvalue.toInt(); } //App Drive (1)/Stop (0) 
      if (button.equals(String("d13"))) { d13 = butvalue.toInt(); } //App Calibrate motor
      if (button.equals(String("d14"))) { d14 = butvalue.toInt(); } //ESP Current Home position
      if (button.equals(String("d15"))) { d15 = butvalue.toInt(); } //ESP Cumulative motor position
      if (button.equals(String("d16"))) { d16 = butvalue.toInt(); } //App rotate clockwise 90 degrees (fast)
      if (button.equals(String("d17"))) { d17 = butvalue.toInt(); } //ESP Millis Count
      if (button.equals(String("d18"))) { d18 = butvalue.toInt(); } //ESP Temporal start Position
      if (button.equals(String("d19"))) { d19 = butvalue.toInt(); } //ESP Temporal End Poistion
      if (button.equals(String("d20"))) { d20 = butvalue.toInt(); } //App Go Home button value
      if (button.equals(String("d21"))) { d21 = butvalue.toInt(); } //App Go Home number of steps required
      if (button.equals(String("d22"))) { d22 = butvalue.toInt(); } //App Go home estimated time
      if (button.equals(String("d23"))) { d23 = butvalue.toInt(); }
      if (button.equals(String("d24"))) { d24 = butvalue.toInt(); }
      if (button.equals(String("d25"))) { d25 = butvalue.toInt(); } //App Motor Start Time
      if (button.equals(String("d26"))) { d26 = butvalue.toInt(); }
      if (button.equals(String("d27"))) { d27 = butvalue.toInt(); }
      if (button.equals(String("d28"))) { d28 = butvalue.toInt(); }
      if (button.equals(String("d29"))) { d29 = butvalue.toInt(); }
               
    }

As you can see, I expect data with identifiers from d10-d29 (not all are currently utilised).

Currently, I send one "packet" per identifier at time and this is quite sparse, time-wise.

However, If I send two discrete messages in quick succession, something goes wrong and the second message is not received. Refer to a question i've raised in the MIT App inventor forums:

Unfortunately, no help there.

I was wondering if I should just send a single packet with multiple data identifiers from the app, in which case i'd need to improve the Arduino code somewhat. I'm really looking for some guidance on how to establishing a more robust parsing protocol that could receive multiple data messages in the one "packet".

My guess is to simply stack them, eg: d10|3|d25|234554643|d18|240\n

I'm just not sure how to resolve the parsing of the final data entry where I need to identify if the next delimiter is a "|" or an \n.

Is the key to this using the .peek() function in some way?

2

So as it turns out, the following simple changes work:

Change my messages from the app to be in the following format:
d12|0|
d10|1|d25|1234|

Basically use a '|' as a backstop to each entry.

Change my incoming parse code to:

//set incoming variable to data sent from
      incoming = espBT.readStringUntil('|'); //get the button descriptor
      String button = String(incoming);
      incoming = espBT.readStringUntil('|'); //get the associated button payload
      String butvalue = String(incoming);

Picks up each complete message one at a time and then follows with the second on the second loop around and so on...

The terminating character '\n' seems to be removed either once i've read the last '|' in the bluetooth serial buffer or as i read the next sent command and the system does away with it at the front end of the 'd**' command.

3

Good that you have a solution. For future using (serial) communication, you can get ideas from Robin's Serial Input Basics - updated.

Assuming d10 .. d29 are variables, you might benefit from the use of arrays.

4

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