BLE Corrupted String

Hi All,

I encountered a rather odd problem with the strings that I receive from my Arduino. I'm using BLE connection and the same MIT AI2 codes (refer to attached) that I use work perfectly fine with the other game application that I created. But somehow, for my first game application, it shows that i'm receiving corrupted string?

My Arduino program also remains the same so I cant pinpoint the exact issue here. Would greatly appreciate any feedback given, thanks!

Lots going on there Kat

  1. Is the variable reading a List?
  2. Remove the list to csv row list block.
  3. Unless your Arduino Sketch is inserting speech marks ("), there are none - you only see them if you populate a textbox or label with the raw data.
  4. After splitting the data in the list, check that it actually contains 3 values before trying to assign them.

Other things:

  1. Usually, using a bar char (|) as a delimiter is better than a comma since commas can be in the data but bar chars likely not.
  2. Ensure that the Main Loop in your Ardunio Sketch allows enough time for App Inventor to process the data, otherwise you will see the error you have reported. Start with a loop time of at least 2 seconds and, only if necessary, tweak it down from there by trial and error. If it doesn't need to be as fast as two seconds, that's great!

Could you show us your Arduino code?
It's worth the time to check data types on the transmitting side.

Hi Chris,

Thanks so much for the help! I'll try implementing the new codes and post updates here again soon.


I am using TinyShield BLE and TinyZero Accelerometer currently and i have modified from the example program given. Here's the Arduino code that I have modified:

#include <Wire.h>
#include "RTIMUSettings.h"
#include "RTIMU.h"
#include "RTFusionRTQF.h"
#include <SPI.h>
#include <STBLE.h>

#include <EEPROM.h>

//Debug output adds extra flash and memory requirements!
#ifndef BLE_DEBUG
#define BLE_DEBUG true

RTIMU *imu; // the IMU object
RTFusionRTQF fusion; // the fusion object
RTIMUSettings settings; // the settings object

// DISPLAY_INTERVAL sets the rate at which results are displayed

#define DISPLAY_INTERVAL 300 // interval between pose displays

// SERIAL_PORT_SPEED defines the speed to use for the debug serial port

#define SERIAL_PORT_SPEED 115200

#if defined(ARDUINO_ARCH_SAMD)
#define SerialMonitor SerialUSB
#define SerialMonitor Serial

unsigned long lastDisplay;
unsigned long lastRate;
int sampleCount;
String data ="";

uint8_t sendLength = 0;
char sendBuffer[30] = " ";

uint8_t ble_rx_buffer[21];
uint8_t ble_rx_buffer_len = 0;
uint8_t ble_connection_state = false;

void setup()
int errcode;


imu = RTIMU::createIMU(&settings);                        // create the imu object

SerialMonitor.print("ArduinoIMU starting using device "); SerialMonitor.println(imu->IMUName());
if ((errcode = imu->IMUInit()) < 0) {
    SerialMonitor.print("Failed to init IMU: "); SerialMonitor.println(errcode);

if (imu->getCalibrationValid())
    SerialMonitor.println("Using compass calibration");

SerialMonitor.println("No valid compass calibration data");

lastDisplay = lastRate = millis();
sampleCount = 0;

// Slerp power controls the fusion and can be between 0 and 1
// 0 means that only gyros are used, 1 means that only accels/compass are used
// In-between gives the fusion mix.


// use of sensors in the fusion algorithm can be controlled here
// change any of these to false to disable that sensor



void loop()
unsigned long now = millis();
unsigned long delta;

if (imu->IMURead()) { // get the latest data if ready yet
fusion.newIMUData(imu->getGyro(), imu->getAccel(), imu->getCompass(), imu->getTimestamp());
if ((delta = now - lastRate) >= 1000) {
SerialMonitor.print("Sample rate: "); SerialMonitor.print(sampleCount);
if (imu->IMUGyroBiasValid())
SerialMonitor.println(", gyro bias valid");
SerialMonitor.println(", calculating gyro bias - don't move IMU!!");

  sampleCount = 0;
  lastRate = now;
if ((now - lastDisplay) >= DISPLAY_INTERVAL) {
  lastDisplay = now;
  RTVector3 accelData=imu->getAccel();
  RTVector3 gyroData=imu->getGyro();
  RTVector3 compassData=imu->getCompass();
  RTVector3 fusionData=fusion.getFusionPose();
  //displayAxis("Accel:", accelData.x(), accelData.y(), accelData.z());        // accel data
  //displayAxis("Gyro:", gyroData.x(), gyroData.y(), gyroData.z());            // gyro data
  //displayAxis("Mag:", compassData.x(), compassData.y(), compassData.z());    // compass data
  //displayDegrees("Pose:", fusionData.x(), fusionData.y(), fusionData.z());   // fused output
  int x =(fusionData.x() * RTMATH_RAD_TO_DEGREE);
  int y = (fusionData.y() * RTMATH_RAD_TO_DEGREE);
  int z = (fusionData.z() * RTMATH_RAD_TO_DEGREE);

  if (x<0) {
    x = (x+360);
  if (y<0) {
    y = (y+360);
  if (z<0) {
    z = (z+360);
  //SerialMonitor.print("x:"); SerialMonitor.print((x));
  //SerialMonitor.print("y:"); SerialMonitor.print((y));
  //SerialMonitor.print("z:"); SerialMonitor.print((z));
  data =(String) x + "," + (String) y + "," + (String) z;
  SerialMonitor.println (data);
  sendLength = sprintf(sendBuffer, "%s", data.c_str());
  // sendLength = sprintf(sendBuffer, "%d", data);
  lib_aci_send_data(PIPE_UART_OVER_BTLE_UART_TX_TX, (uint8_t*)sendBuffer, sendLength);


void displayAxis(const char *label, float x, float y, float z)
//SerialMonitor.print("x:"); SerialMonitor.print(x);
//SerialMonitor.print("y:"); SerialMonitor.print(y);
//SerialMonitor.print("z:"); SerialMonitor.print(z);

I'm not an expert on the hardware and software you are using, so all I can suggest are some things to check, that might cause garbage to be sent ...

  • You define a baud rate of 115200, faster than the usual default of 9600. A mismatched baud rate between serial components might cause misalignment of the transmitted and received bit signals, causing garbage to arrive.
  • Loose wires?
  • Your comments say you are using objects. Are you printing an object instead of one of its string attributes?
  • Are you printing uninitialized text areas?

Hi Kat

Sketch. Is this your own work?

  • Variables should never be defined/declared in a loop() !
  • It's good that elapsed time is used for the loop(), but how it is implemented is unusual

I'm not familiar with Lib_aci_send_data and there is nothing in App Inventor's BLE Block that needs the exact length of the data - App Inventor just wants a flag marking the end of the data stream. It's also not necessary to concatenate the values into a single string if you use the Serial library.
Example (flesh this out from your existing data collection code):

//ArduinoToApp.ino Chris Ward 28/06/2020 13:09:18 

// include the library code:
#include <SoftwareSerial.h>

unsigned int igUpdateTime;

void setup()
//use this baud rate first
//tweak by trial and error later
       igUpdateTime = millis();

void loop() {

	  if(millis() - igUpdateTime > 1000)  {
          //Loop approx every 1 seconds 

           igUpdateTime = millis();

           if (Serial.connected())
                     //To App via Bluetooth
                     //This tells App "End of Data"
                     //= Ascii Line Feed Char Num 10