Forum Archive

I need to write "A00101A2" to a BLE Relay and cannot figure out how. The following does not work.
self.peripheral.write_characteristic_value(c, '0xA00101A2', False)

Have no idea how to format "A00101A2" for the Pythonista core bluetooth module. I can use something like "nRF Connect" or "BLE Hero" to set the value and it works.

Executing self.peripheral.write_characteristic_value(c, '0xA00101A2', False) sets the value to something else thats not A00101A2

You might try swapping bytes -- BLE is supposed to send dat in little endian byte ordering, but your iPad is a big endian device.

Since you are sending 32 bits, you might also need to swap the upper 16 and lower 16 bits -- sometimes characteristics contain two "fields".

Any insight on how to do that? Reading up and trying to learn....
My background is mostly Bash and Powershell scripting.

@Aarown1017 the easiest is just to swap manually, if you are always writing a fixed value

Instead of
self.peripheral.write_characteristic_value(c, '0xA00101A2', False)
Try
self.peripheral.write_characteristic_value(c, '0xA20101A0, False)
Or maybe
self.peripheral.write_characteristic_value(c, '0x01A0A201', False)

(A byte is two hex characters)

Can you read back this characteristic? If so, what are you getting when you read it back?

What device and GATT are you using?

Sorry, looking back at docs, the data needs to be a byte string. You passed an actual string.

What you want is probably

self.peripheral.write_characteristic_value(c, 0xA00101A2.to_bytes(4, 'little'), False)

Or maybe
self.peripheral.write_characteristic_value(c, 0xA00101A2.to_bytes(4, 'big), False)

Or possibly
self.peripheral.write_characteristic_value(c, 0x01A2A001.to_bytes(4, 'little'), False)

Or maybe
self.peripheral.write_characteristic_value(c, 0x01A2A001.to_bytes(4, 'big), False)

@JonB said

looking back at docs, the data needs to be a byte string

I had seen that but all examples in the forum are strings, I did not understand as I never had used BLÉ and I did not answer.

@JonB said:

Sorry, looking back at docs, the data needs to be a byte string. You passed an actual string.
self.peripheral.write_characteristic_value(c, 0xA00101A2.to_bytes(4, 'big'), False)

THIS WORKED!!!!! I cannot thank you enough.
Hope enough people find this thread because there were so many unanswered threads online.

This is the device I have:
https://www.amazon.com/dp/B07MKMFP6H/ref=cm_sw_r_tw_dp_46SC6RK392XTNVHDRE89
https://drive.google.com/file/d/1aUKZaKQnj6v4Jz-hOtDGEAVyBKMAJmQk/view?usp=sharing