Getting BLE to behave on the Pi

Although the following list isn't exhaustive, you should know the following terms before navigating the BLE options and to understand responses on forums.

• Central and Peripheral. The central is the device that scans for the peripherals, which should be advertising. For example, the central might be your phone and the peripheral your Fitbit wristband.
• Scanning. The central scans for peripherals but might only scan for peripherals advertising a certain service. You need to make sure the service being advertised and the service being scanned for match up.
• Services. Services are the way devices describe themselves and each service is a collection of characteristics, which are roughly analogous to properties of a class or fields in a database table.

What happens when BLE communication doesn't work? Where are the logs? What should you try?

Know your debugging tools. The first thing to check is compatibility of the BLE dongle. You'll either get errors about not being able to write to the device or just get nothing back from if it's not BLE compatible. I encourage you to research the device before buying.

On the Raspberry Pi you can run the hcidump tool installed earlier. This monitors the BLE status and reports on all advertising and each connection made. To use it, run

hcidump -X

in one terminal on the Raspberry Pi. In another terminal, start up your BLE advertising script, such as

sudo node ble-peripheral.js

which dumps the activity.

This tool is useful when a central isn't connecting to the peripheral and you can't work out at what point the failure is occurring. The output of hcidump shows you how far in the advertising, interrogating, and pairing process you got and will help find out at what point things break. In such cases, this log might report what point you've reached.

The rfkill command is worth checking out because sometimes the BLE capability will be disabled on the Raspberry Pi, blocking all activity. To use this, run rfkill, which shows which are blocked:

# rfkill list
0: hci0: Bluetooth
     Soft blocked: no
     Hard blocked: no
1: phy0: Wireless LAN
     Soft blocked: no
     Hard blocked: no

Although specifically for bleno, adding the following options to the command line provides more output, which is also helpful. Remember you're looking for the BLE to start advertising and, if it does, for a connection to be attempted:

sudo DEBUG=hci-blue,l2cap-ble      node test2.js