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My supplier tells me that communication between 2 bluetooth devices requires authentication by an app. When reading online I believe it should be possible, but am not 100% sure.

One article from EDN gave me the impression that it should be possible, but I cannot oversee completely.

My application is a smart battery charger, which will allow the owner of an electric bicycle to charge the battery not full but e.g. 80% to save lifetime (like Tesla c.s. does - this roughly doubles the lifetime). A tester with Bluetooth at the e-bike dealer then (optionally) measures the exact capacity of the battery and marks the voltages at each 10% State of Charge.

I intend to do this BT communication without an app as that would be too complex. Here is the procedure:

The charger sends a data set (including device ID) and the tester receives. After measuring is completed the tester sends the updated dataset back to the charger. After verifying if the device ID is the charger's, the charger then updates the data set and is hence calibrated. Is this approach (working without App) feasible in your view?

It would help me best when I can copy an answer and pass this along to my supplier. They are a Chinese company and I prefer to work with them - even when they do not (yet) have hands-on experience. They are very experienced in EE.

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    \$\begingroup\$ Communication between 2 BT devices is possible. How are you going to read it without an app to control and extract the raw data? \$\endgroup\$
    – Jason Han
    Commented Aug 15, 2017 at 7:17

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I mean, you could use something like a BT 4.0 beacon mode to broadcast information, but really: shouldn't you be pairing?

From an application point if view, wouldn't it be pretty bad if just anyone in the vicinity of your bike could update the battery calibration? They could essentially reduce the usable battery to nearly nothing, I.e. brick your bike, without even touching it, if you don't build in some constraints on who and when can interact with the battery controller via Bluetooth.

A Bluetooth pairing is exactly that: making sure you're talking to the right partner.

I imagine this would work like the following:

Since the service guy would need to have an electrical connection to the bike for measurements, anyway, normal Bluetooth pairing happens, initiated by bike firmware. The secret pin exchange necessary for that happens through a one wire (twi) bus or similar when plugged into the measurement device.

That way, an attacker would at least have to have physical access to your bike to brick it

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  • \$\begingroup\$ Thanks for your response Marcus. Meanwhile I also got a tip from an EEin my network who said there are different BT modules, e.g. BT 04, 05 and 06 (what are the differences). They would exist in "serial interface modules" (e.g. BT-04M) in Master and Slave versions and "Bluetooth Adapters" (e.g. BT-M4). I also see the BT replaced by HC (maybe manufacturer code?). \$\endgroup\$
    – James TH
    Commented Aug 15, 2017 at 9:30
  • \$\begingroup\$ Please note that this is about the charger, not the electronics on the bike. The bike dealer has a dealer version to calibrate the smart charger and must be able to do that with any smart charger. I thought the procedure was safe. The dealer version would be the master, requesting the data from the slave (charger). To avoid that multiple chargers within range (not common but possible) would send the data. We could implement that 10 LED's on the charger start flashing -or something- and the user then pushes a button to invoke data sending. Can the serial interface module also talk to an app? \$\endgroup\$
    – James TH
    Commented Aug 15, 2017 at 9:39
  • \$\begingroup\$ I don't know any of the devices you're referring to. So, I don't know. \$\endgroup\$
    – Marcus Müller
    Commented Aug 15, 2017 at 11:25

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