SEND HEX VALUES WITH BLUETOOTH APP INVENTOR 2

[Paulo Benetti]

Hello guys,

I am developing an app to make the capture of data from a central alarm.

I need to send the data to HEX but so far had no success.

The communication specifications are: baud 2400 / data size 8 / no parity.

Ex. I send 6-byte hex (A5 DD 02 20 03 ED) and central returns

Hex 19 bytes (00 00 00 00 00 00 FF FF FF FF ...)

Can anyone help me with this.

Thank you very much.

[Abraham Getzler]

If you drag in a Web component in the Designer, that will give you access to conversion blocks you can use without going out to the Web.

See attached for a hexify routine that will create any hex string you want, and a sample call that will create a Byte Order Marker (BOM) of x'FEFF'.

There is also a block that can reverse this, called URIEncode (decode?).

ABG

[Paulo Benetti]

Hi ABG

i'm test your blocks and some number hex is okay.

When the number hex is betwin 00 - 7F, the conversion is right and the bluetooth send the conversion has no problem,

 but when the number hex is betwin 80 - FF the conversion is wrong. note the picture attached.

What's the problem?

Thanks and regards,

Paulo

[Abraham Getzler]

First, a word about my BOM and stripBOM procedures.

They were included by me as an example of how a call to hexify() looks like,

but they are not appropriate to your problem.

They are intended for use only to preprocess a file coming from Excel with

two specific hex bytes in front.  

Remove them.

Second, about the wierdness when you pass 7F ...

This is probably about UTF-8 encoding, which is the default on the Bluetooth client.

Google UTF-8 for explanation as how and why it works.

Your receiving device (unavailable to me) is probably set differently in its encoding strategy.

ABG

[Paulo Benetti]

Ok, the problem is the signed number

a value is 8bits but is -127~127.

How i sent unsigned number with bluetooth, you know?

[Abraham Getzler]

http://ai2.appinventor.mit.edu/reference/components/connectivity.html#BluetoothClient

How about 

BTClient1.SendBytes(create list(0,0,...,255,255)) ?

ABG

[Abraham Getzler]

Have you tried BTClient.SendBytes?

See attached.

I'm not sure this will work.

Let us know?

ABG