Multiple sensor data via bluetooth on App ERRORS

I'm working on an Air quality monitoring project using an Arduino nano 33 IoT and 4 sensors (an MQ7, MQ135, DHT22, MP503). I'm also using an HC-05 bluetooth module to send the sensor data from all of the sensors to my MIT App. The app runs smoothly for some time and then a few errors pop-up.I found that a few of the sensor readings appear at the wrong labels in the app. I have attached the screenshots of the errors. Also attaching my arduino code and MIT aia file.
AEROSENSE.aia (760.3 KB)

Arduino Code:

#include "DHT.h"
#define PIN_MQ135 A0
#define DHTPIN A2
#define MQ7_PIN A6
#define MP503_PIN A4

#define DHTTYPE DHT22 

//MQ135 mq135_sensor(PIN_MQ135);

void setup() {

void loop() {
  float humidity = dht.readHumidity();
  float temperature = dht.readTemperature();
  int MQ135PPM = analogRead(PIN_MQ135);
  int MQ7OP = analogRead(MQ7_PIN);
  int MP503OP = analogRead(MP503_PIN);

String airQuality;
if (MQ135PPM <=200 && MQ7OP <=100 && MP503OP<=300){
  airQuality = "Good";
  } else if (MQ135PPM<=400 && MQ7OP<=350 && MP503OP<=600){
  airQuality = "Moderate";
  } else {
  airQuality = "Bad";

      Serial.print(F("Temperature: "));

    Serial.print("  Humidity: ");

    Serial.print("  MQ135 Analog value: ");

    Serial.print("  MQ7 Analog value: ");

    Serial.print("  MP503 Analog value: ");

    Serial.print("  AIR QUALITY: ");

    //Bluetooth send part

Be sure to use println() at the end of each message to send from the sending device, to signal end of message.

Only use print() in the middle of a message.

Be sure not to println() in the middle of a message, or you will break it into two short messages and mess up the item count after you split the message in AI2.

Do not rely on timing for this, which is unreliable.

In the AI2 Designer, set the Delimiter attribute of the BlueTooth Client component to 10 to recognize the End of Line character.
Also, return data is not immediately available after sending a request,
you have to start a Clock Timer repeating and watch for its arrival in the Clock Timer event. The repeat rate of the Clock Timer should be faster than the transmission rate in the sending device, to not flood the AI2 buffers.

In your Clock Timer, you should check

  Is the BlueTooth Client still Connected?
  Is Bytes Available > 0?
     IF Bytes Available > 0 THEN
       set message var  to BT.ReceiveText(-1) 

This takes advantage of a special case in the ReceiveText block:

Receive text from the connected Bluetooth device. If numberOfBytes is less than 0, read until a delimiter byte value is received.

If you are sending multiple data values per message separated by | or comma, have your message split into a local or global variable for inspection before trying to select list items from it. Test if (length of list(split list result) >= expected list length) before doing any select list item operations, to avoid taking a long walk on a short pier. This bulletproofing is necessary in case your sending device sneaks in some commentary messages with the data values.

Some people send temperature and humidity in separate messages with distinctive prefixes like "t:" (for temperature) and "h:" (for humidity).
(That's YAML format.)

The AI2 Charts component can recognize these and graph them. See Bluetooth Client Polling Rate - #12 by ABG

To receive YAML format messages, test if the incoming message contains ':' . If true, split it at ':' into a list variable, and find the prefix in item 1 and the value in item 2.


Thank you for the reply, I'll try doing this.

@ABG I think I've solved the errors. I also went through similar issues faced by other users and the fixes you suggested for them(replacing delay with millis() and such). I ran my app for like 15 mins now without any errors popping up. Thanks a lot and really appreciate you spending your valuable time to help me :smiling_face: .

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