How can I implement a custom characteristic which displays the value in range of -100 ... 0 ... 100 %?

[Thomas Lehwald]

Hello,

I've tried to implement a custom service with a custom chacteristic, that shows the values per notification in the MCP (Master Control Panel) in percentage.

I played around with the ble_gatts_char_pf_t structure, provide the unit with the value proposed here:

0x27AD

percentage

org.bluetooth.unit.percentage

but without luck.

.format = BLE_GATT_CPF_FORMAT_SINT8;

.exponent = 1; // ???

.unit = 0x27AD

.name_space = BLE_GATT_CPF_NAMESPACE_DESCRIPTION_UNKNOWN; // tried also: BLE_GATT_CPF_NAMESPACE_BTSIG

Is there any example, which shows, how to setup this structure properly?

It should finally works like the battery level (which is handled in bas.c).

I can see the changeing values during received notifications in MCP, but only as hex value.

Where did I go wrong here?

Thnaks in advance.

Regards Thomas

[MartinBL]

Is this Master Control Panel for Windows? It has been a while since I used it, but as far as I remember it doesn't show anything other than hex values. 

[Thomas Lehwald]

Hello Martin,

yes, the tool I used is the MCP for Windows.

But I also tried out another tool on the iPhone called "LightBlue", with the same results. Only hex values are shown.

I guess, that this "tools from the stock" doesn't take care about the format representation, is this right?

Thanks

Thomas

[MartinBL]

It is up to the application to read the presentation format and parse the data accordingly. I don't know about LightBlue, but at least MCP does not. Neither does nRF Connect for mobile. 

[Thomas Lehwald]

Hello Martin,

thanks for your assistence.

So, it seems, I must live with this circumstance until a custom app can handle the format representation correct.

Best Regards

Thomas