Writing hex value to BLE characteristic

[Aarown1017]

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

[JonB]

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".

[Aarown1017]

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

[JonB]

@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?

[JonB]

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)

[cvp]

@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.

[Aarown1017]

@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