How can I compare variable with number?

Hello, I'm new one using App Inventer

I'm connecting arduino and app inventor with bluetooth module.
From Arduino, App inventer get arduino sensor data with float number like 34.32
I made blocks to see recent arduino sensor data per minute.

I wnated to compare arduino sensor data per minute with 57.
If sensor data is higher than 57, i want to make the label's color to red.
I update every arduino sensor data to 'Variable' which name is 'recv' as you can see in the pic.

But, that runtime error is causing.
What should I do.


Gobal variable recv is empty and math blocks "hates" empty strings so use an if then statement to check if global recv is not empty and if it is number then proceed with math operation


[quote="Porco, post:3, topic:56694, full:true"]
Thanks for advise.

I initialized recv as '0' but still same. T.T

PS. I realized that I send arduino sensor data with 'println'.
Will it be matter to compare with number 57?

I got solution Thanks

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Here is standard advice on message Delimiters, which should apply for this case:

Please see the Delimiter article in FAQ

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:

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.

You are not collecting the data correctly Porco. 'Bytes Available to Receive' is effectively a flag. Instead, use a maths block, -1, which means 'collect all bytes of stream'.


You can also make use of the is number? block to verify a value is a number before passing it into the comparison block:

1 Like

Dora Paz mentioned checking the value is a number too, it's a very tidy way to test viability.

Porco, please tell the forum of your solution, it could help many others.

That doesn't matter, AI can handle it as a number. Why is your code removing a segment from the value received? Have you set the Bluetooth delimiter byte?


can you tell your solution here?