Arduino Uno Rev 3 + MIT App Inventor + Bluetooth Module HC05 + Door Magnetic Switch

The state can be changed in the UNO firmware or the App Inventor software with one or two lines of code or it can be changed in the hardware at the switch by altering how the magnetic switch is connected. Which method would you prefer?

I am planning go display change of state in the MIT App Inventor Application which I built. In a way that, I want to use this App to monitor whether the door is close or open.

I am just confused whether my codes in the Adruino IDE is correct and at the same I am also doubting my programming block in MIT App Inventor.

Do you think it is possible to do this Sir?

Hello Neil, I am extremely sorry for the delay in replying to your reply as I did not know why suddenly I could not log in to the e14 and I couldnt find my thread at all . Little did I know, it was actually being reported as a spam but it is okay as during that period of time I managed to solve the connecting issues. The current status is that, I managed to connect my HC-05 to an Android Phone. However, I faced another issue which is some instability in terms of transferring data. When the door magnetic switch forms 1 (when both are attracted to each other) the status which should be displayed in my app is supposed to be "AVAILABLE" and whe nthe door magnetic switch forms 0 (when the switch is not attracted to any magnet) the status which should be displayed in my app is supposed to be "UNAVAILABLE".

The current status is that, when the door magnetic switch forms open circuit it satisfies the criteria which is in the app it displays "UNAVAILABLE".
However, when the door magnetic switch forms closed circuit, the status keeps switching from "UNAVAIALBLE" to "AVAILABLE". I cannot receive "AVAILABLE" as the status as it keeps switching between the two status.


In terms of connection.
HC05 RX is connected to TX of Arduino (Pin 1)
HC05 TX is connected to RX of Arduino (Pin 0)
Door Magnetic Switch is connected to Pin 2 of Arduino.

Both modules use common GND and common Vin.

In terms of programming block I used in MIT App Inventor:

Here is a short video which shows the issue I am facing:

I hope to hear from you soon Sir. Cause I am just stressing over this thing right now. I have been stuck for quite sometimes (1 month)

Hi kikovader Sadly, your video is still encoding, so I am unable to watch it!

However, now that you have a connection, you have been able to supply some information that shows up several problems:

1. The Arduino code you posted your reply of November 13 has the Reed Switch connected to Arduino Pin 4; in your most recent reply, you say it is connected to pin 2
2. Your Arduino code uses Serial.print to send either "detected" or "notDetected" to both the IDE serial monitor and the HC-05, simultaneously. You need to include a delimiter., otherwise the AppInventor Bluetooth block will almost certainly get confused! The AppInventor  block expects a default of Cr/Lf, so you should use Serial.println instead.
3. You are checking the Reed Switch every 100 mS - delay(100); What time have you set the AppInventor Clock1 block to fire at? The default is 1 second, if you haven't changed it, then your AppInventor Bluetooth buffer will be flooded. You need to fire the AppInventor Clock1 slightly faster than the Arduino Loop - say 90 mS, to ensure that you read each message from the Arduino as soon as it is sent
4. In AppInventor, you only check for "notDetected" and assume that if you didn't receive "notDetected", then you must have received "detected". In fact the way things are set up, you are receiving an almost continuous stream of text, containing no delimiters. What you actually read in AppInventor is a matter of luck!
5. I'm pretty sure your Clock1 block could be simplified:  The second If:

          Is almost certainly redundant and may well be contributing to your problem

Not wishing to preach about step-wise development, but if you had actually stepped back and temporarily displayed within your User Inteface what you were actually capturing in AppInventor, then you might have better understood your problem. You would certainly have been able to provide more information here to help with diagnosing the problem.

Hope this helps

Neil

neilk  wrote:

 

Hi kikovader  Sadly, your video is still encoding, so I am unable to watch it!

 

...

The same for me. neilk, can you try to reload it?

Hi Neil, I am deeply sorry for the late reply again because I have been busy with examinations lately as I am still a student.

I would like to reply to your bullet points.

1. Initially, it was connected to pin 4 because I have connected pin 2 and 3 to LEDs just to check whether my Door Magnetic Switch is working perfectly by looking at the LED. When Door Magnetic Switch forms a closed circuit, LED connected to pin 3 will light up and when it forms an open circuit, LED connected to pin 2 will light up.

2. I understand about this statement but I am still quite unsure on how to use a delimiter in Arduino IDE. I have been trying to research for some resources also but I did not find anything useful at all. Correct me if I am wrong, based on my past researches delimiter is basically to split a string or character?

3. The delay I set in Arduino IDE was 100ms and just now I checked the MIT App Inventor for my clock interval it was measuring at 10ms. Do you think this might contribute the instability issue which I have currently?

Just to keep everyone on the same page. The current problem I have right now is that in the Mobile Application which I built using MIT App Inventor it does not show stable results from Arduino Uno using HC05 Bluetooth Connection. I want the App to work under these two conditions:

Condition 1: When Door Magnetic Switch forms a closed circuit (1), I want the App to display "Available"

Condition 2: When Door Magnetic Switch forms an opened circuit (0), I want the App to display "Occupied"

As of now, the App can fulfil Condition 2. However, when the Door Magnetic Switch forms a closed circuit (1), the App is unable to display a Fix "Available". It will keep displaying BOTH condition 2 and 1 at the same time when it forms a closed circuit. The app keeps switching its conditions within miliseconds. So it is not fix and stable. What might be the causes of this issue?

I have tried to post the video also but I am unable to do so

I am sorry I am just a slow learner trying to learn coding sigh.

Hi Kim

Here is a slightly modified version of your Arduino Sketch:

//Define the pins being used.
//Connect the Door Magnetic Switch or Sensor to pin 4.
//
int ledOpen=2;
int ledClose=3;
int switchReed=4;


//When the Door Magnetic Switch formed Closed Circuit = 1


//When the Door Magnetic Swich formed Open Circuit = 0


void setup()
{
//Initialize serial communication with Bluetooth Module HC-05
  Serial.begin(9600); //Serial.begin is used to set the speed of communication in bits per second. By default it is 9600. In short, changing the number will change the speed of transferring data.
  pinMode(ledOpen, OUTPUT);
  pinMode(ledClose, OUTPUT);
  pinMode(switchReed, INPUT);
}
void loop()
{
  if (digitalRead(switchReed)==HIGH)
  {
    digitalWrite(ledOpen, LOW);
    digitalWrite(ledClose, HIGH);
    Serial.println("detected");       // Note use of Serial.println to send a newline after the string "detected" has been sent
  }
  else
  {
    digitalWrite(ledOpen, HIGH);
    digitalWrite(ledClose, LOW);
    Serial.println("notDetected");    // Note use of Serial.println to send a newline after the string "detected" has been sent
  }
    delay(1000);                      // 1 second delay between reads
}

I have also attached a very basic App Inventor app which should read data from the Arduino and display it on the screen of your Android device. You just need to import it into your AppInventor environment. It includes the design and the blocks.

I say it SHOULD work, because I don't have an HC05 set up available for me to test it on!!

Hope this helps

Neil

HELLO NEILLLLLL!!!

I AM SO HAPPY THAT WITH THE HELP OF YOUR PROGRAMMING BLOCKS FOR THE APP IT FINALLY WORKS OMG. THANKKKKK YOU SOOOO MUCH!!! IS IT POSSIBLE FOR ME TO TREAT YOUR A CUP OF STARBUCKS COFFEEEEEE OMG HAHA. All i just need to do right now is trying to change the colour of the text sent to the app but I will figure it out myself. THANK YOU SO MUCH ONCE AGAIN OMG HAHAHAHA...

Can I have your emailll I REALLY REALLY WANT TO TREAT YOUR STARBUCKS OMGGG!

You are welcome, Kim. Very pleased that it worked for you .

You can't change the colour of the text you send from the Arduino to the App. You can, however, change the colour of the text displayed in the App with 2 simple blocks:

Good luck with the rest of your project

Neil

Hi Neil, Its been long since we ever talked.

Recently, I tried to test out the App using MIT App Inventor and the code using Arduino Uno Rev3.
Though, I modified a few lines of the code, the issue which I had previously occur. The Bluetooth does not want to send information to the App which you built using MIT Inventor App.

//Define the pins being used. 

//Connect the Door Magnetic Switch or Sensor to pin 4. 

#include <SoftwareSerial.h>

SoftwareSerial mySerial (0, 1); //RX,TX

int ledOpen=2; 

int ledClose=3; 

int switchReed=4; 

//When the Door Magnetic Switch formed Closed Circuit = 1 

//When the Door Magnetic Swich formed Open Circuit = 0 

void setup() 

{ 

//Initialize serial communication with Bluetooth Module HC-05 

  Serial.begin(9600); //Serial.begin is used to set the speed of communication in bits per second. By default it is 9600. In short, changing the number will change the speed of transferring data. 

  pinMode(ledOpen, OUTPUT); 

  pinMode(ledClose, OUTPUT); 

  pinMode(switchReed, INPUT); 

} 

void loop() 

{ 

  if (digitalRead(switchReed)==HIGH) 

  { 

    digitalWrite(ledOpen, LOW); 

    digitalWrite(ledClose, HIGH); 

    Serial.println("detected");       // Note use of Serial.println to send a newline after the string "detected" has been sent 

  } 

  else 

  { 

    digitalWrite(ledOpen, HIGH); 

    digitalWrite(ledClose, LOW); 

    Serial.println("notDetected");    // Note use of Serial.println to send a newline after the string "detected" has been sent 

  } 

    delay(1000);                      // 1 second delay between reads 

}

The underlined part is the new line which I added. Even though few months ago you adviced me not to use the RX/TX pins from the arduino uno.

I am confused!!!!!!!!

In your post of December 16 2019 you said it was working!

What exactly did you have working?

Were you using a different model of Arduino?

In your latest post, you have misunderstood the use of SoftwareSerial. The whole point of SoftwareSerial is to define and use a different pair of pins!

See my blog here: MIT AppInventor, HC06 and Arduino: much improved method of sending data via Bluetooth - Part 1, The Arduino Side

Hello Neil.

Back then, the Arduino Uno can send the correct data to my App through HC 05. However, as i progressed with the projects by adding more modules. The accuracy of the Arduino just disappeared. I was extremely confused too. The bluetooth can connect to the App, however, the app does not receive any data at all.

I tried to troubleshoot this by checking the health of my HC05 and my HC05 seems to be transmitting and receiving correct data. I checked this by shorting the RX and TX. 

I also checked my magnetic door sensor and it is working perfectly.

After making sure that my HC05 and door magnetic sensors are working perfectly. I decided to troubleshoot by using the IDE programme which u prepared previously together with the .aia file. To my surprise, it is somehow working but the data received by the App keeps toggling from “Available” to “Occupied” even when there is no changes to the door sensors input.

I have read the blog which you have attached alongside. Should I follow the code you type for IDE eventhough you are using HC06 while im using HC05?

Please advise Sir.

Hello Neil.

Back then, the Arduino Uno can send the correct data to my App through HC 05. However, as i progressed with the projects by adding more modules. The accuracy of the Arduino just disappeared. I was extremely confused too. The bluetooth can connect to the App, however, the app does not receive any data at all.

I tried to troubleshoot this by checking the health of my HC05 and my HC05 seems to be transmitting and receiving correct data. I checked this by shorting the RX and TX. 

I also checked my magnetic door sensor and it is working perfectly.

After making sure that my HC05 and door magnetic sensors are working perfectly. I decided to troubleshoot by using the IDE programme which u prepared previously together with the .aia file. To my surprise, it is somehow working but the data received by the App keeps toggling from “Available” to “Occupied” even when there is no changes to the door sensors input.

I have read the blog which you have attached alongside. Should I follow the code you type for IDE eventhough you are using HC06 while im using HC05?

Please advise Sir.

Ii should work with your HC05 - when used in the mode you are in, HC05 and HC06 are supposed to be interchangeable.

Alright. In short, I should just try the code u used for your HC06 am i right?

yes

Hi Neil,

I hope you are doing fine despite the current epidemic happening right now.

I have tried to understand the Guide for your HC-06 and I also tried it out but it looks like there the issue still persist. The current issue as of now is that, the data send by arduino stuck at "notDetected" regardless of the condition of the magnetic switch reed. (in a sense whether it forms HIGH or LOW).

That's the schematic diagram of the mini project and yes, I still insist on using PIN 0 and PIN1 as my RX and TX because I just dont know why suddenly out of the blue it is not working at all. I am extremely confused because when u helped me last december everything seems to be fine. I did not even change anything and I have already checked the health of my components and everything seems to be fine. My Magnetic Switch Reed is working perfectly as I had already test it out to light up an LED. I have also tested my Bluetooth module by shorting the RX and TX together and both transmit and receive the same exact data.

I am just confused right now. Really. What might be the issue right now cause this is so strange.

There are 2 significant differences between your schematic and the the first schematic in my blog:

1. In your schematic you are powering the HC-05 from the Vin pin on the Arduino board, rather than the 5v pin - why?
2. In my schematic, the TXD pin of the Arduino (D1) is connected to the RXD pin of the HC-06 via a voltage divider, which reduces the 5V output of the Arduino to around 3,3V. The HC-05 and HC-06 devices are clearly marked as being restricted to a 3.3 v input - at least mine are!

It's possible that you have damaged your HC-05.  In any case, I suggest you change things and try again.

However, If you read my blog carefully, you will note that in my early experiments, using Arduino pins D0 and D1 to communicate with my HC-06 had initially worked. The reason I switched to using SoftwareSerial and 2 other Arduino pins, was because it stopped working for me....... the very problem you now seem to have.

Neil

I've just noticed that your schematic doesn't have a pull-up resistor on Arduino Pin D4. This means that the pin is "floating" when the reed switch is OPEN and pulled down to ground when the reed switch is CLOSED.

I suggest you connect a 10k resistor between Arduino pin D4 and 5v.. It might help.

Neil