I want to end pairing between 2 cc2541 module, but when 2 modules are pair no
AT-command executed and I cant end the pairing.
How can I end the connection?
I did this in my project by connect power of BT to digital pin of Arduino, and when need to stop pairing, just set the digital pin to low. may be this way will help you
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I'm having a hard time understanding why a Bluetooth connection is able to be made without either pairing or trusting a device. I'm using bluetoothctl and and can connect two devices without pairing them first by using "Scan on" on the central side and "Advertise on" on the peripheral side.
could someone explain why this is happening?
From the Bluetooth client example at http://people.csail.mit.edu/albert/bluez-intro/x502.html, it seems I can simply connect to a remote Bluetooth socket as long as I have the Bluetooth MAC address of the device.
If I can simply connect to a remote Bluetooth device, I am wondering what exactly does Bluetooth pairing do. When is pairing really needed?
Update:
From How does Bluetooth pairing work?, it appears the final result of pairing is that an encryption key gets stored on both sides. I assume, when you open a remote socket connection, the call is intercepted by the local bluetooth daemon. In turn, the daemon encrypts the data and sends to the remote device. The daemon on the remote device decrypts the data and sends to the remote client application:
Device1Client-->Device1Daemon-->Device2Daemon-->Device2Client
Is this assumption correct?
Yes, your assumption is partially correct. Encryption is one of the uses of Passkey.
Bluetooth pairing is necessary whenever two Bluetooth devices connect to each other to share resources. A trusted relationship is established between the devices using a numerical password, commonly referred to as a passkey. Depending on how often one Bluetooth device connects to another, the user might opt to have the passkey saved for future connection attempts or prompt to enter the passkey each time the devices request communication with each other.
This is already explained on Stack Overflow please check- How does Bluetooth pairing work?
In the below answer, I will try to explain what is not mentioned in the above link or answers.
In Pairing process, when the initiating device sends a ‘Pairing Request” to the other device. The two devices then exchange I/O capabilities, authentication requirements, maximum link key size, and bonding requirements. Basically, all this phase consists of, is the two devices exchanging their capabilities and determining how they are going to go about setting up a secure connection. It is also important to note that all data being exchanged during this phase is unencrypted.
Now the question is why this Phase is needed?
As mentioned- “two devices exchanging their capabilities.” The pairing should happen between compatible device there is no point in Pairing you Mouse with a Headphone as Mouse capabilities are different than Headphone.
One more use of Pairing is – “determining how they are going to go about setting up a secure connection.” Here the frequency hopping pattern is determined for two reasons-
To avoid Middle Man Attack.
To avoid Collision
Bluetooth uses 79 radio frequency channels in the band starting at 2402 MHz and continuing every 1 MHz. It is these frequency channels that Bluetooth technology is "hopping" over. The signal switches carrier channels rapidly, at a rate of 1600 hops per second, over a determined pattern of channels. The hopping pattern is determined well during the pairing process so that no other device will know in which band of the frequency the data is being transferred at an instance. Its rare case that frequency hopping pattern can be the same for a couple of devices communicating hence collision is avoided.
Note: If any third device is able to capture the passkey then it can replicate the whole communication pattern and capture the data being transferred. This is how the BT Sniffers work.
I am not able to cover all the details as per SIG specs. I hope the above answers give you a clearer picture of the need for the Pairing process. Feel free to point out, if you want me to explain any specific point in detail.
Below are the reference Links for more information-
http://large.stanford.edu/courses/2012/ph250/roth1/
https://www.bluetooth.com/blog/bluetooth-pairing-part-1-pairing-feature-exchange/
I implemented the org.bluez.Agent1 interface using QDbus and I would like to set a fixed pin (that I will provide to the users) in order to authenticate all the pairing request and reject them if the pin is wrong. The agent capabilities should be "NoInputNoOutput" because the project will be deployed on the RaspberryPi 3 without keyboard or display. Is there a way to deal with this? Thank you
You should not initialize the capability as "NoInputOutput" for fixed key pairing. NoInputOutput means there is not display and there is no keyboard/UI possible for this device. Mentioning this capability for your Agent when registering with BlueZ means, instructing BlueZ (bluetoothd) not to call any Agent API for authentication.
This is typically useful to autopair without any manual intervention. You can see this sample code, which uses NoInputOutput capability to connect the device without any intervention.
What you need is "DisplayOnly" capability to instruct BlueZ to call "DisplayPinCode" or "DisplayPasskey" based on SSP support of your device.
You can implement DisplayPinCode/DisplayPasskey in your Agent to reply constant PIN always. So the Bluetooth device which tries to connect can use the same constant PIN for pairing.
Here Display Pin /Passkey is just the naming convention or hint to Agent developers to write wizard/UI or any form of display operations. But you can completely ignore the displaying operation and reply with static/constant 6 digit key for pairing.
Typically this Agent API is called by Bluez (in rasperry pi) when the device (iPhone/Android mobile/any bluetooth capable device) trying pair calls "RequestPasskey" or "RequestPinCode" from the device end.
We had the same issue in a project, and i moved on LE device do to the fact that apple device are only capable to connect to LE device for "safety" reasons.
I don't have that much ref to that but if this could help you in your researches.
I am pretty new to IoT and BLE. What I want to achieve is to write on GATT characteristic of at least 100 peripheral devices simultaneously or in a very short period of time(i.e. less than 100ms). Currently my peripherals are Ble nano (nRF51822) with custom GATT service running on them. I am using my Mac as central BLE. I am using Node.js and noble to implement the central. I want to know if such thing is possible at all and if possible, please link me to an example code. :)
You should note that Bluetooth chips for computers are usually (quite arbitrarily) limited to only a few simultaneous connections. Common values are between 3 and 14. Even if you connect a few at a time, send the characteristic value, disconnect and then connect next devices it would be impossible to do this within 100 ms. If you want to send the same data to everyone you should instead let your computer advertise and the nrf devices scan. That way you broadcast the data instead.
I have Bluetooth SPP module SPP-C / SPP-CA , it is cheap module that should work the same way as well known HC-06 / HC-05 modules.
I have got one problem, everything works, module is communicating over serial interface pairing etc... but i can not enter the AT mode to change device name pin or baud rate. Does anyone had the same problem and how to solve it ? there is a very small data published and sellers are not responding.
So I assume that someone may help with that situation. http://www.ebay.com/itm/Bluetooth-Module-UART-Serial-Interface-SPP-CA-works-with-YZXstudio-USB-Monitors-/201414967094 that's the module. it is based on Beken BK3211 chip.
It seems that nothing special is needed to enter command mode on the SPP-CA module I have.
Whenever you connect or disconnect by bluetooth, the module will print:
CONNECTED
.. serial data is transferred ..
+DISC:SUCCESS
When the module is disconnected, you can execute AT commands such as AT+BAUD just like with HC05 modules.
3 years later and I've looked everywhere for an answer to this question and finally stumbled upon the solution by fiddling away.
I am connecting via an FTDI module using Teraterm software to enter commands.
You need to power up the FTDI and BT modules by plugging into PC USB. open Teraterm and set up to see the COM port.
Now you have to momentarily connect GND to port 11 on the BT module to 'reset' the module. The module will power down and back up again and in doing so will enter AT mode and you should be able to communicate with the module.
Good luck
Old question however still relevant, I found the solution! It is pretty simple, you can use an breadboard and some jumper wires however you can also create an adapter like I did. Like explained in this document with AT-commands, you need another UART (serial connection) to program the SPP. The SPP must not connected to anything (discovery mode) to be able to program it.
You can do this, like I did, with another SPP or you can use serial programmer or an Arduino. Notice that the serial connection is 3V, so when using an Arduino you need some resistors (1K and 2K) to create a voltage divider (google it).
The schematic is pretty simple (when not using an Arduino), I designed this adapter:
You need these components to create the adapter (and maybe some wires):
Connect everything like in the schematic above (STATE and EN are not connected), insert the modules (take care of pin orientation!), insert an USB cable and connect it to some power source.
In Arduino IDE, select the com-port you want to configure and launch the Serial monitor, you can now enter AT-commands to configure the one that is not connected:
Done! That is pretty easy right? When you want to configure the other, disconnect the one that is connect and connect the other one. An overview of AT-commands can be found in the document in provided link above.
Hopes it helps ;-)