How often can a Center 'notify' a Peripheral in BLE

Question

I have an RC car that I built using arduino, a bluetooth usb dongle, and a ps3 controller. The car has several functions (lights, sounds) along with driving around.

I want to replace bluetooth dongle and the ps3 controller with a BLE module (I have the HM-10) and I want to use web bluetooth. So the controller will be a virtual one served from a secure website.

My question is: Is a setup like this possible with the current version of web bluetooth?

And: How often can a Center (My computer/website) notify the Peripheral (the RC car) to start/stop/turn/play sound/etc... ? In general, what limitations will I (if any...I'm sure there are some or I wouldn't be posting this) run into with this setup vs the simple bluetooth dongle/ps3 controller.

I hate to be too general but being new tech, any other comments/insights/pitfalls are welcome!

Answer 1

Yes, this is possible. Some examples:

• RC Car from dev board with Web Bluetooth
• Sphero controlled with Web Bluetooth

You could even keep the Dual Shock 3 as an optional input device by using the Gamepad API.

Regarding notification frequency, neither Chrome nor the Web Bluetooth API impose any artificial limitation on BLE activity at that level. However, that's not to say that Chrome's architecture won't add some small amount of overhead. Additionally, all of this is heavily hardware dependent, both on the central and the peripheral, so it's difficult to even ballpark expected performance.

Good luck! Sounds like a neat project!

Answer 2

Normally you don't use GATT Notifications when you send data from central to peripheral but rather GATT Writes. There are two write types: Write Without Response and Write With Response. Which are available depends on the peripheral firmware setup.

Write With Response requires one round trip so the throughput is directly related to the connection interval.

For Write Without Response packets, many such can be sent in one connection event so if you use these you are only limited by the link throughput. Note that CoreBluetooth (iOS/Mac OS X) which Web Bluetooth uses for those OSes has an own interpretation of the BLE specification that drops outgoing packets if the app sends them quicker than they can be sent over the air (this applies only to Write Without Response, not Write With Response). The buffer size differs between versions but is on the order of around 20.