Signal received on MiT APP Inventor not showing the first digit

[Lâm Quang]

Hello. Can anybody help me with this. I am connecting Pulse Sensor with Bluetooth Hc05 to display on MIT Inventor App. But the problem is the heart rate number display is sometimes missing the first digit. For example, the heart rate is 104 but it sometimes show 04..

[Riccardo Risi]

It's better if you show your block code downloading it with "Download block as image" functionality.

Bye

[Lâm Quang]

Thanks you very much, Sir

[ABG]

You are using the Clock Timer to chop off pieces of the incoming data stream

blindly.

There is a way to insure you get only complete messages, using message Delimiters ...

Use println() to separate messages when you transmit.

Set Delimiter = 10 in BlueTooth Designer.

Check for Bytes Available > 0 in blocks,

but then request -1 bytes to get only full  messages.

See https://groups.google.com/forum/#!msg/mitappinventortest/lVaCyAeWm_4/ADjvy05wAwAJ attachments.

ABG

[Lâm Quang]

I have done it. Thanks you very muchhh. Can you please explain it for me, Sir? I still cant understand why it work

[ABG]

I have done it. Thanks you very muchhh. Can you please explain it for me, Sir? I still cant understand why it work

The HC05 uses asynchronous serial communication.

The link has many articles that explain it.

There are more articles on BlueTooth in the FAQ at

https://groups.google.com/forum/#!msg/mitappinventortest/wqJin0qO8M0/8xUafdROAgAJ

The HC05 delivers bytes one after another like

a supermarket checkout counter conveyor belt.

If the customer behind you at the checkout counter 

 is in a rush and rude, they

might start loading their groceries onto the belt before

you have finished loading yours onto the belt.

That would cause the checkout clerk to mix up the orders.

It takes extra effort to block such people when loading the belt.

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

 ReceiveText(number numberOfBytes)

Receive text from the connected Bluetooth device. If numberOfBytes is less than 0, read until a delimiter byte value is received.

ABG