Difficulties writing to a characteristic

[thijsputman]

First off all, thanks a lot for the great work!

Have a question which might be a bug-report (but I'm a bit out of my depth here): I've recently been toying with a TC66C (BLE USB-C load meter) and node-ble. Got one up and running just fine. Got a second device now; this appears to be a new hardware revision. It uses a different set of characteristics (have those figured out) and somehow I'm unable to write commands to this new device...

In a nutshell:

To get data from the device, write a command to 0000ffe2-0000-1000-8000-00805f9b34fb and get notifications on 0000ffe1-....

Using node-ble, I retrieve the 0000ffe2-... characteristic and get its flags:

[ 'write-without-response', 'write' ]

Indicating I should be able to write to this characteristic?

Attempting to write anything to it gets me a DBusError: Write not permitted though.

Looking at the same device via GATTTool, I get this (relevant bits only):

[XX:XX:XX:XX:XX:XX][LE]> characteristics
...
handle: 0x001c, char properties: 0x0c, char value handle: 0x001d, uuid: 0000ffe2-0000-1000-8000-00805f9b34fb

[XX:XX:XX:XX:XX:XX][LE]> char-desc
...
handle: 0x001c, uuid: 00002803-0000-1000-8000-00805f9b34fb
handle: 0x001d, uuid: 0000ffe2-0000-1000-8000-00805f9b34fb
handle: 0x001e, uuid: 00002901-0000-1000-8000-00805f9b34fb

Using the above information, if I issue this command:

gatttool -b XX:XX:XX:XX:XX:XX --char-write-req --handle=0x001d --value=626e657874700d0a # ASCII: bnextp\r\n

It works as expected. The device receives the command and acts upon it (there's a little screen on the device; this command tells it to cycle to the next page on that screen – so I can see it work)

What am I missing on the node-ble/D-Bus end?

Edit: remove irrelevant addition

[thijsputman]

It seems I lost sight of the forest for the trees... (or more accurately, the obvious for the UUIDs 🙂)

The solution to my problem is in version 1.5.0 of node-ble (specifically, the changes described in #20):

In the options passed to writeValue, type should be set to command. Using the default type (reliable) causes a ERROR: DBusError: Write not permitted to be raised when trying to write to the characteristic.