CODEWITHSUNDEEP
iosbluetoothcore-bluetoothbluetooth-lowenergy
Dan F
Dan F

Reputation: 17732

Transmitting data with CoreBluetooth

I'm developing an iOS app with an accompanying Bluetooth LE peripheral. The one step I don't seem to be able to solve is how to actually transmit the data from my app to the peripheral or vice versa.

What I've built so far is a test app that can connect to my sample Bluetooth peripheral, and read all of its services/characteristics/descriptors. It can toggle notifications for a given characteristic, and write to given characteristics. It is just this last step of "transmit n bytes to the peripheral, and receive m bytes from the peripheral" that I can't seem to figure out.

Looking at the External Accessory Framework (what I would use if Apple would actually give me MFi approval for this project), they give you input and output streams on a given session to communicate with the accessory, but no such object exists for CoreBluetooth.

Is this simply an oversight on Apple's part on the functionality of CoreBluetooth? Or do I simply need to develop my own Bluetooth service profile to handle the inflow/outflow of data to and from the peripheral?

Upvotes: 5

Views: 5989

Answers (3)

alera729
alera729

Reputation: 41

You can build a custom profile with private services and characteristics and have it work kind of like SSP; that's the way I'm using my BLE module to get data from some sensors to my app. The module I bought (Microchip's RN-4020) already has a custom profile made specifically for this known as MLDP (Microchip Low-energy Data Profile).

The way I get the data in my iOS app is by subscribing to the private characteristic, thus being notified when the values are updated. So far it has been working great, and the data rate can go up to 20 kbps according to Microchip (I haven't tested its limits, since I don't need much speed). Here's a link to Microchip's product page: http://www.microchip.com/wwwproducts/Devices.aspx?product=RN4020

Good luck!

Upvotes: 3

Lowell Bahner
Lowell Bahner

Reputation: 51

You can use the bluetooth.org 'Immediate Alert Service' uuid=1802 with characteristic uuid=2A06 with property=write_no_response to send one byte values to your peripheral device from your iPhone. The peripheral device must be programmed to act on the data that is sent. For example, you might use a button on an iPhone app to send a hex address that causes one or more port pins to turn on or off on the peripheral. While this is not using the Alert Service as it was intended, it does provide an easy way to test out data transfer to a peripheral device. The same process could be used to send sequential data bytes similar to a serial data stream. I have not yet tried sending more complex data streams. The write_no_response does not provide any feedback to the app as to whether the data was received by the peripheral.

The IOS TemperatureSensor.xproj is an example of code for reading temperature data from a peripheral. The OSX HealthThermometerClient.xproj has the code needed to decode the somewhat complex thermometer data structure. The IOS TI-BLE-Demo.xproj TIBLECBKeyfob.m has code for reading and writing characteristic values, such as, reading temperature or battery levels from a peripheral device.

Upvotes: 2

TJD
TJD

Reputation: 11896

LE is fundamentally designed to work with these GATT based profiles, which are suited for monitoring sensors, not for data streams. While LE does allow for additional L2CAP streams to be opened for custom protocols, Apple's CoreBluetooth doesn't provide access to do so.

Upvotes: 3

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