Difference between blocks at receive text from bluetooth

[Panagiotis]

Ok i am sorry maybe its my fault... lets start over....
I have a sensor which sends temperarure values in this format.....
26.3/30.4

1. What will you receive on the first block and what on the second one?
2. What happens when new data arrive?
3. How will these blocks understand that we have reached a complete reception so to update the variable with new data?

Thank you very much

[Kumaraswamy]

@Panagiotis

What will you receive on the first block and what on the second one?

The block which is ReceiveText(NUMBER_HERE) receives some part of the data. Let's say you have the block below.

Someone has sent you the value 26.3/30.4 then only the number of bytes mentioned in the above block will be received. So you should get the value 26 as the first 2 bytes.

In the second block, you receive the whole available bytes or data.

Note: I have never worked with the Bluetooth component.

[Panagiotis]

Thank you very much for your answer.....

@Kumaraswamy

In the second block, you receive the whole available bytes or data.

so in a new data arrival will update the previous one or wil have 26.3/30.4 28.8/31.2 ???

[Kumaraswamy]

Some person sends data of value 26.3/30.4. Still, you have not used the below blocks

@Panagiotis

then the data will get append or added like "26.3/30.4" is the first value. The person sends another data again like "28.8/31.2". Here you have not used the blocks so when you use the block after the person send data two times then you should get the data "26.3/30.4 28.8/31.2".

Let's say still the person has not sent the second data. "28.8/31.2" value is still waiting to be received. When you receive it completely, there will be no data left so it becomes empty. Next times he sends the second value then the process will repeat.

[Kumaraswamy]

I hope I have not made the post confusing .

[ABG]

Here is the standard boiler plate advice for BlueTooth Delimiters ...

Please see the Delimiter article in FAQ

FAQ Section: Bluetooth < version 4 (BlueTooth Client) and Arduino

Arduino HC-06 tutorials Arduino USB - Pavitra and Thunkable Arduino via USB Delimiter usage for receiving one message per ReadText DHT22 Temperature or Humidity, no Clock - kio4.com How to send CR the hard way http://www.martyncurrey.com/android-mit-app-inventor-auto-connect-to-bluetooth/ Instructables YouTube course on Arduino/AI2 - Magesh Jayakumar Martyn Arduino Bluetooth sketch Sending Slider Data to Arduino - Neil Kenyon Turning a LED on and off with an Arduino, a HC-06 and Andr…

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

ReceiveText(numberOfBytes)
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.

[Panagiotis]

really nice explanation!!! The thing that i dont really like with this reception technique is that if the microcontroller stucks and doesn't send the delimeter byte the program of the mit appinventor also stucks and waits for this particular byte, so to continue...But if a certain amount of time passes...then the companion crashes.... Do you mind if i post my aia file to explain what is happening wrong and if you can help me solve it out??

regards

[ABG]

@Panagiotis

Do you mind if i post my aia file to explain what is happening wrong and if you can help me solve it out??

Please export your project and post it here.

[Panagiotis]

Ok please read this first before reading the blocks so to understand whats happening..
I use 2 ds18b20 sensors with a pic microcontroller.
When everything is on the first run , then you have to add the sensors to the pic microcontroller. One sensor will be used in the input and the other one on the output. When you press the button to add a sensor to the microcontroller then the app sends '*' and waits 'Con_OK' when this is done then you select position of the sensor (in or out) and when it has finished the registration then the microcontroller sends 'Reg_OK' to inform the app that it was a successfull registration.
After that on every 3 seconds the app sends '?' to to inform the microcontroller that request the temperature and the microcontroller sends it in a format of 25.5/30.2
So far so good.... and everything works as expected.....
The problem arises when you want to add a new sensor...
Then it runs the add sensor timer but although the microcontroller sends the text 'Con_OK' it runs the else part which is that the connection has failed.
But after that it appears on the main screen which makes me believe that the buffer does not empty.

Thank you all for your concern Panagiotis

Sup_Sup_Monitor_One_Screen2.aia (97.0 KB)

ps. I have also used the bytes available to receive with same results

[ABG]

I see three Clock Timers, working at cross purposes ...

This connection timer is presumptuous, assuming instantly available input, with a guaranteed '/'. It also fails to check if input is available, before asking for input and blocking if none available.

I would only use this timer to send the '?' polls, and only if connected.

This timer also fails to check if input is available before asking for it, also potentially blocking.
It also assumes it will only ever receive 'Reg_Ok', and discards anything else, like /-delimitted readings.

This also is like the Reg_Ok timer, but with Con_Ok.

Consider consolidating all 3 timers into one timer, responding to input by content:

(draggable)

In the process routine, put a three way if/then/elseif test to respond appropriately to

• Reg_Ok
• Con_Ok
• a message with '/' in it (text CONTAINS block).

[Panagiotis]

You are awesome!!!! Really appreciate it!!! I will try it out and and post my results. But unfortunately i cannot find these 2 blocks at mit appinventor...

And what is your proposal for the interval period of this clock? 100mSec?
Also i cannot get rid of the other clock since i need on every 3 secs, the app to request the temperarute from the microcontroller sending the ? character

[dora_paz]

Global message is a global variable , use blocks to set it

As for the procedure use mutator to add slots , press little gear

[Panagiotis]

Thank you very much for your answer but i still cant find the first arrow i drew.... "call process message block" There isnt such a block on mit appinventor procedures tab.

Regards

[dora_paz]

Different look of the same block

External Inputs

Inline Inputs

[ABG]

@Panagiotis

unfortunately i cannot find these 2 blocks at mit appinventor...

Here is your own copy, ready to drag directly into the Blocks Editor ...

@Panagiotis

And what is your proposal for the interval period of this clock? 100mSec?
Also i cannot get rid of the other clock since i need on every 3 secs, the app to request the temperarute from the microcontroller sending the ? character

100 msec should be okay, as long as you use a shorter interval than the transmitting side, to avoid getting swamped.

Having extra clocks to transmit '?' is okay, as long as those don't try to grab and hog the BlueTooth input stream.

[Panagiotis]

Hello again unfortunately it didnt work.....

Although it receives the Con_OK......
it runs the" else part" with the message W-T-F:Con_OK

****EDIT: I re-wrote the word Con_OK and now seems to work as expected!!! I am currently making tests.... Perhaps it had to do with the drag i did to your post.... Maybe some corrupted characters??? I will post the results!! Also i changed the variable from message to global message

[Patryk_F]

Con_Ok is not the same as Con_OK

[ABG]

Pardon my case errors.

[Panagiotis]

After some tests i did it works like a charm!!! thank you very much!!!! But since i like to learn can you please explain me the blocks below?

1. When does the process run? When it reaches the delimeter byte?
2. I really cant understand the part of -1 it says..... If there is 1 or more bytes available then set the global variable to the received text... But where does the -1 assosiates?

Thank you again!!!

[Patryk_F]

-1 need not understand, you need to know that when we add -1 to read, then the read block stops the program and reads the bytes until it reads the delimiter byte. Next program continues and executes the procedure.