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

Question

Hello, so this is my first time learning on how to use a Microcontroller like Arduino Uno and currently, I am planning to do on some mini project which uses these items below:

1. Arduino Uno Rev 3

2. Bluetooth Module HC-05

3. An App to receive the data which I created using MIT App Inventor

4. Door Magnetic Switch.

To be very honest I do not know where to start but I have already designed the User Interface of the Application without the Programming Block. I want it to work in away, when the Door Magnetic Switch formed closed circuit, it will send 1 or "ON" in the App through the Arduino Uno. However, when the Door Magnetic Switch formed an open circuit, it will send "0" of "OFF" in the App.

Is this possible?

Please help me. I am begging you. Please

neilk · Accepted Answer

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 
 Attachments: Classic_BT_basic_data_from_Arduino.zip

neilk · Answer

Looking at your Arduino code, I can see that you are intending to connect the HC-05 Bluetooth module directly to the hardware Rx and Tx of the Arduino. Whilst this will work, it can be unreliable. It's much more reliable to use another pair of digital pins to communicate with your Bluetooth device. Have a look here at my blog:

https://www.element14.com/community/people/neilk/blog/2018/02/14/mit-appinventor-and-arduino-much-improved-method-of-sending-data-from-arduino-and-receiving-on-android-device

I have used HC-06, but it will also work with HC-05 - HC-06 is a slave only device. HC-05 can be programmed as a master or slave device. I think you could actually use HC-06 in your application.

Your MIT AppInventor blocks don't include all that I have found necessary to connect to a Bluetooth device and don't contain any blocks to disconnect from the Bluetooth device.

I always use a connection structure similar to this:

And I also include a disconnection block:

The rest of your blocks look OK, superficially, but I would always develop something as complex as this in small steps, testing each step as I go along. If you take this approach, you will be able to debug your project as you go along.

Hope this helps

Neil

neilk · Answer

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

kikovader · Answer

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)

kikovader · Answer

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!

kikovader · Answer

Besides that, here is the User Interface for the App that I built.

When the magnetic door switch formed a closed circuit, 1. I want "Status 2" of "Flex Stro 1" to display "Unavailable"

When the magnetic door switch formed an open circuit, 0. I want "Status 1" of "Flex Stro 1" to display "Available"

I am just unsure whether I have done it correctly and I have not tried this whole thing yet. But there is something inside me which tells me that it is wrong so yea.

It would be nice if someone can help me out

neilk · Answer

Hi Kim

Your set up is so complex (relatively speaking) that we cannot see the wood for the trees.

Using the emulator doesn't help matters! It's much easier and more reliable to use the MIT AI2 Companion App on an Android device.

I'm a bit confused as to your motivations in this project - using AppInventor when you don't have an Android device on which to run the App??

So, why connecting the HC-05 directly to the Uno Rx and Tx, is unreliable:

Firstly, the presence of the HC-05 across the Rx/Tx lines sometimes, but not always, stops a new sketch from being uploaded the the Uno. To rectify this it is necessary to disconnect the HC-05 from the Uno Rx/Tx

Secondly, the presence of the HC-05 across the Rx/Tx lines sometimes, but not always, stops the HC-05 from accepting a connection request on the Bluetooth side. To rectify this it is necessary to reset the HC-05, by disconnecting the +5V supply.

So back to the project:

You need to simplify your system so that it can be shown to work step by step. I suggest you do this by reproducing the stages in my blog which I referenced in my previous reply.

If you cannot reproduce the steps in my Blog, then we need to delve deeper, and you will need to provide a schematic of the Uno and HC-05 connections.

Until you can demonstrate that you can communicate with the Uno/HC-05 system, using something like Blueterm, there is little point in worrying about the detail of the AppInventor design and blocks.

Hope this helps

Neil

kikovader · Answer

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.

kikovader · Answer

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.

Jan Cumps · Answer

digitalWrite(ledOPen, LOW);

You need to fix a typo in this line. Lower case P

Serial.print(notDetected");

Opening quotes missing.

You could take care to only communicate if the status of the reedswitch changed between digital reads.

neilk · Answer

yes

kikovader · Answer

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.

neilk · Answer

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

phoenixcomm · Answer

Yes but No, Question: How are you determining the door to be "opened" or "closed"? Answer: You need a door switch normally they are a mico switch activated by a magnet! and btw you can get date and time from a public time server (very easy to build one) NTP or Network Time Protocol if you use timestamp then this will involve some network access and the network (Ethernet Shield) do { if ( door == open ) { # maybe send msg door was opened @ time do { } while( door == closed ); #maybe send msg door was closed @ time } else; # fall through }while ( something = 0 );

kikovader · Answer

Hi Sir, I am sorry for the delay in replying to your help. But here is the code:

//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.

//Set the speed of transferring data to default speed.

pinMode(ledOpen, OUTPUT);

pinMode(ledClose, OUTPUT);

pinMode(switchReed, INPUT);

}

void loop()

{

if (digitalRead(switchReed)==HIGH)

{

digitalWrite(ledOPen, LOW);

digitalWrite(ledClose, HIGH);

Serial.print("detected");

}

else

{

digitalWrite(ledOpen, HIGH);

digitalWrite(ledClose, LOW);

Serial.print(notDetected");

}

delay(100);

}

kikovader · Answer

Hi Neil,

I am sorry if I took too long to reply to you but I have been trying to understand what are the differences if I connect my HC-05 to RX TX directly and what if I did not connect it directly.

I tried to follow my original plan which is connecting the HC-05 to RX TX of the Arduino Directly, however faced some issues.

I tried to use the MIT App Inventor Emulator to do the try out. At first it shows this:

When Bluetooth button was picked, the next screen shows nothing, basically it is just black and I do not know how this happen It does not even display the list of Bluetooth Connections available for me to connect. I did not download the App to my phone because I am using iOS L:(

.

In terms of programming block, here is my programming block which I have modified according to your suggestion which is really makes sense:

And the programming code for the Arduino is below:

//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.

//Set the speed of transferring data to default speed.

pinMode(ledOpen, OUTPUT);

pinMode(ledClose, OUTPUT);

pinMode(switchReed, INPUT);

}

void loop()

{

if (digitalRead(switchReed)==HIGH)

{

digitalWrite(ledOpen, LOW);

digitalWrite(ledClose, HIGH);

Serial.print("detected");

}

else

{

digitalWrite(ledOpen, HIGH);

digitalWrite(ledClose, LOW);

Serial.print("notDetected");

}

delay(100);

}

Could you help me to solve this issue Please

neilk · Answer

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: 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 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. 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 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! 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

kikovader · Answer

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.

neilk · Answer

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

Jan Cumps · Answer

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?

neilk · Answer

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

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

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