I'm developing an android BLE app in which i try to establish a stable Connection between the app and a BLE device.
To achieve this i want my app to keep the BLE device data in shared preferences or somewhere.
After app close, i'd like my app to retrive this data and attemp a connection without scan for devices.
I prefer to avoid scanning every time becouse scan gives me a lot of problems and it takes time.
How can do it? Is there a way to save BLE data?
You need to store the Bluetooth Device Address (AB:CD:EF:01:02:03) of the device in for example shared preferences or in a sqlite db. Then use https://developer.android.com/reference/android/bluetooth/BluetoothAdapter.html#getRemoteDevice(java.lang.String) when you later restart the app to retrieve a BluetoothDevice object. Once you have the BluetoothDevice object you can use the connectGatt method as usual.
There are some undocumented things you need to keep in mind however. Due to some horrible design flaws in Android's BLE API there is no way to tell it if you mean the given address is a Public Address or a Random Address. (You can read more about different address types at https://devzone.nordicsemi.com/question/43670/how-to-distinguish-between-random-and-public-gap-addresses/). The getRemoteDevice method should take an additional parameter "random address/public address" but it doesn't. Without the correct address type, the Bluetooth controller cannot connect to the device.
Android's BLE stack has some internal heuristics to "guess" if the address is public or random, but unfortunately that differs between Android versions and also if you use autoConnect=true or false. However if you have bonded the device (https://developer.android.com/reference/android/bluetooth/BluetoothDevice.html#createBond()) then it will store in its internal DB whether the given address is public or random. If the peripheral you want to connect to uses a random resolvable address it can handle that as well if you use bonding. Therefore I strongly suggest to use bonding.
If you don't use bonding you will need to scan before you connect to the device, since when you start a scan and a device is detected, Android's BLE stack will temporarily (until next restart of Bluetooth) remember the address type for an address.
I will continue on Emil's answer.
Thanks #Emil for the 'big picture'.
Google API is flawed and you can't use getRemoteDevice() because it only understand 48bit address and do not know about all BLE address types.
You can't use Bonding if the device is dumb (anyone would be able to bond to it).
So your only solution is a Bluetooth scan.
However, since Android6 (Marshmallow) the user has to give location permission to apps using Bluetooth scanning. If you don't permit, it won't work.
So if you buy a Bluetooth thermometer (or heart-rate monitor or whatever), you have to permit the app to access location of your phone (or tablet).
That's absurd!
#Emil call it a 'Google flaw'. You may also call it a 'Google machination'.
If I was a thermometer designer, I would add a push-button to accept bonding. It seems ridiculous because the button will only be used once.
[1]: https://www.polidea.com/blog/a-curious-relationship-android-ble-and-location/
Related
We want Android to automatically connect to our custom made BLE peripheral.
Our peripheral should regularly (but infrequently) advertise and attempt to Indicate some time-sensitive sensor data to the phone. Thus we want the phone to be ready to connect at any time.
Generally, you can pair a smart watch with an Android, and Android will then automatically connect to the smart watch whenever it is in range. So we believe our use case should be feasible.
I read a lot of answers that advise to set the "autoconnect" parameter to true when connecting. I have tried that and the reconnections don't persist through a reboot or even after disabling and re-enabling Bluetooth on Android. This answer by Brian says I should scan in the background, but Android made this unrealistic. If I use a foreground service, my users will hate the app. If I use a background service, I may miss the peripheral's attempts to connect during Android's Doze and the code becomes error prone.
Ideally, I want to do something like what Emil said in his answer here. Please read the follow up question and response.
However, we can't see our app through Android's Bluetooth settings. We can only connect to the peripheral and pair with it using our app (or nrf Connect). In desperation, I tried modifying the peripheral's advertising flags. Then I could see it in Android's Bluetooth settings. But when I try to pair using Android's settings, the attempt fails because the peripheral is not in "pairing mode".
We are building both the app and the peripheral, so we can change both. I want to know if our use case is possible and what we need to do to get it working. We are using the STM32WB for our peripheral.
Use a combination of these techniques:
Bond the device. This might be needed due to the crappy Android Bluetooth LE API design that doesn't take the "address type" as an extra parameter when connecting to a device. When you connect using the Bluetooth device address, it looks up a device with this address in the bonding info, and uses the corresponding address type (random or public).
Use connectGatt with autoConnect set to true. This means no timeout, as well as auto-reconnect if the connection drops. Even if it takes days or weeks until the peripheral starts advertising, it will still work.
Listen to https://developer.android.com/reference/android/bluetooth/BluetoothAdapter#ACTION_STATE_CHANGED and restart your connections when Bluetooth is re-started.
Use a Foreground Service in your application's process to prevent the OS from killing the process. Users can nowadays hide the annoying notification in Android settings if they want to.
Listen to https://developer.android.com/reference/android/content/Intent#ACTION_BOOT_COMPLETED to start your app after boot, including your Foreground Service.
Listen to https://developer.android.com/reference/android/content/Intent#ACTION_PACKAGE_REPLACED to automatically restart your app after an app update. See https://stackoverflow.com/a/2134443/556495 for some instructions.
The best approach is to make sure your peripheral can be bonded. Once you have bonded with it you can ALWAYS use autoconnect because Android stores info about bonded devices and you don't have to scan for it anymore. Hence you avoid the issues with scanning in the background.
Although that resolves the need for scanning, you still need to deal with your app being killed once it is in the background. Using a Foreground Service is still the best solution to my knowledge. I don't think you users will hate your app for it...
I need to estabilish a brief communication between a BLE master and a BLE peripherical device.
Until I have to use the mobile phone I have no problems, since I select the bluetooth device from Android, I can connect to it and then I can receive data simply writing them to HM-10.
BUT, this approach is battery expensive, since the BLE scanning is more battery expensive than the BLE advertising (right?). So I want that the mobile becames an advertisor and the HM-10 takes the ROLE of Slave.
BUT, I still don't understand if it is possible to connect to other devices: I tried AT+CONN and it always fails (AT+CONF). Is there any way to send brief data from the HM-10 to the advertisor, even without connecting?
Even my firmware looks slightly different from the readme! For example,AT+LN is present in the documentation but it appears to not exist. Does a better version of the firmware for this device exist, or, are sources available somewhere? I installed the HM-Soft V705 (lastest).
Thanks
UPDATE 1:
#ChrisStratton Ok, I have some intresting news: I was already following your idea (phone advertise sometimes, while HM-10 always scan and tries to connect to the service if it sees it, then HM-10 send some data, phone answer). I managed to make the phone visible from HM-10 (don't ask me how!). I am using the BLE Tool Android app to test everything. Now, the central problem now is that HM-10 won't connect to the android service even if the advertisor is connectable (see attached images).
I am sospicious that the AT+CO (that I discovered is a kind a replacement of AT+LN, but I am not sure) can help, but i don't know how.
Is there any simple way to check if an existing BluetoothDevice object is still reachable without performing a new scan?
I am writing an app that scans for devices and goes through connecting to each one at a time to populate a device list with some information about each device, which I acquire while connected to the device. Every now and again, I would like to go through my device list and remove any devices that are no longer active/in range. What is the best way to do this?
You could try to connect to the devices to find out if they are still around, but keep in mind, that devices will change their mac address from time to time.
I would suggest to use scanning to find out if the devices are still around. Also you may want to add an identifier into the advertisement packages, so you don't need to relay on the mac address.
I am doing an APP to configure/control battery powered devices using Bluetooth.
The devices are not "visible" to save energy.
I have a ready list of about 50 device. The list contains the Bluetooth MAC address and the required PIN to pair.
When the APP starts up, I prompt the user to select a device from the list.
So now I want to automatically bind with the device, if not already done yet, without the need for the user to enter the PIN again.
I googled a lot, but did not exactly find what I was looking for (at least what I understood).
But I have to admit that I am pretty new to android programming and might simple not get the hint-
I also assume I do not use the right terms to search.
I found some "hacks" that simply suppress the PIN entry.
Can someone help me out here?
I already had the APP up and running if I manually bind the device, so the SPP communication is not the problem, it's mainly how to provide the PIN for connection.
Thanks a lot.
You can create new bond with bluetooth device by calling BluetoothDevice setPin(byte[] pin) and createBond() methods. You need also set BLUETOOTH_ADMIN permission.
public boolean createBond ()
public boolean setPin (byte[] pin)
I am developing an application which connects devices over bluetooth and exchanges messages. It works fine for paired devices, but I would also like it to automatically pair devices that are not paired. Like for example it could store and use the same PIN for pairing requests, I just dont know how to manage this request programatically in my applciation, how to automatically set and send the PIN when you get a pairing request and how to initiate such a request with the predefined PIN code.
Any snippets or thoughts would be highly appreciated! :)
EDIT:
I know its risky, I am developing this app for emergency situations only where no other means but bluetooth is available. Also is there maybe a way of premature pairing with devices without even connecting to them? Like lets say there is a list of MAC Addresses of those devices and I can use them to generate a bond with that devices so that they appear paired on my device?
You can't do this. To do what you want to do would create a huge security risk. Think about it, my device just comes anywhere in bluetooth range of yours and now I can send you anything I want without you knowing? You can't really do this and I highly recommend not trying to subvert it.
Reflecting the setPin method allowed me to send the pin automatically to the other device. I had to implement it in a broadcast receiver that is listening for pairing requests. Although I cant get rid of the dialog it just stucks there on the screen and I dont know how to close it (programatically) and continue the bonding procedure since this dialog is called from inside connect() which is a blocking method. I am not giving up on it yet though :)
With Bluetooth version 2.1 and above there is a method of pairing called the 'just works' association model. This is the lowest security method of pairing and has no protection against man-in-the-middle attacks.
However, this will provide a secure, encrypted link without the need to exchange pin numbers or verify device ID.
The API on different platforms may differ but the underlying HCI messages require that you indicate that your device (or one of the devices) has the following IO capabilities:
No Keyboard, No Display.
As you might have guessed, this is a mode for very
simple devices that use Bluetooth, such as a speaker or headphones.
If you can find the API to configure that, then the 'just works' association mode of Secure Simple Pairing will be used for pairing.
The next step is to store the link keys e.g. bonding. Many devices e.g. mobile phones, will still create a dialogue box to the user to ask if they want to 'remember this device', as user authorisation is specified by the BT specifications... but that's another problem.