I have to write a BLE application on an embedded device and there are some features where I'm not sure if BLE supports that or whether I've to create some wrapper around everything or if it's maybe not possible at all. The gerenal descriptions of Bluetooth and BLE I found around the internet usually only cover the overall functionality but don't go in too much detail. If this post gets too complex I'll split it up into different smaller ones.
I use the STM32 BlueNRG-MS chip
1. Discoverability (resolved)
The user has to be able to disable the BLE function in case there are several devices in reach. I see that there are functions aci_gap_set_discoverable() or aci_gap_set_non_discoverable() but altough I set it to not discoverable I can still see it in the LightBlue App on my mobile. How would I correctly disable the BLE functionality of a device to make sure no one can see it or connect to it?
Update: Okay that has been a mistake from my end, if I call the aci_gap_set_non_discoverable() function it is actually undiscoverable. So that's fine.
2. Only accept connections of paired devices
I'd like to achieve a behavior such that, if you have an unpaired phone you have to set the BLE device into a pairing mode in order to connect. If the phone has already been paired, the BLE device shall accept the connection request regardless of whether it's currently in pairing mode or not. Is this what the whitelist should be there for or do I have to do this manually by saving the address of the device after successful pairing? If whitelist is the right approach, I read that newer phones cause issues with whitelisting because they change their address on a regular basis, how can I handle this? That's actually where I thought I'm gonna work with the "discoverability".
3. Automatically reconnect
I'm not sure if this topic has to be handled on the BLE device or on the mobile phone. E.g. my phone is paired with my car's radio, so whenever the phone is in the car it automatically connects - how is this done? It's still the phone that acts as central device I assume?
Related
I bought one of these:
https://www.aliexpress.com/item/Smart-finder-Key-finder-Wireless-Bluetooth-Tracker-Anti-lost-alarm-Smart-Tag-Child-Bag-Pet-GPS/32806261079.html
As far as I can tell it is a BLE (Bluetooth Low Energy) location tag.
I downloaded the app for it onto my iphone, and the app instantly recognised it and connected to it. The iPhone app seems to know how far away the tag is - it has a little map of the local area and says how many feet away. I was able to set the device name via the app, but I'm not sure if that set it locally or on the tag itself. The iPhone app also has a "find" button - when you press it, the tag beeps.
So I want to know how I can program this thing myself. I want to be able to identify it when it is nearby, connect to it and make it beep. I've searched for quite a while but not come up with much.
I'm assuming (wrongly/rightly?) that there is some general standard or approach for talking to these BLE location devices and carrying out the basic functions with them - but what is that standard - where is the documentation?
Does anyone have any idea how to program these BLE location tag devices?
BLE devices typically communicate using GATT, either using standard GATT services, or custom ones. The command to make it beep is probably implemented using a custom GATT service.
For finding out the distance to the beacon, typically the RSSI is used. This is a measure of the received power. It needs to be compared to the output power at the emitter. Usually beacons will put their output power in advertisement data, so it can be used without connecting to them. Here since the app is also able to send commands to the beacon, chances are it keeps a connection to it and has a custom GATT protocol to retrieve the output power.
Here is what I would suggest:
Read up on BLE, especially advertising and GATT. For instance read this for advertising and this for GATT. The full BLE spec is available here but should be used for reference and not introduction
Sniff the communication between your device and your phone. You can see this other answer of mine to get started
Replicate the communication protocol in you own app. For that you'll need to use your target platform's BLE libraries. For instance for iOS it is CoreBluetooth
To test bluetooth scalability, I want the same device (a Raspberry Pi or a laptop) to emit several BLE advertisements. So far, I have tried using bleno (NodeJS), hcitool and CoreBluetooth for OSX, but I can not setup more than one.
Is this a hardware/system/bluetooth limitation? Has somebody managed to do this?
Different bluetooth devices have different maximum advertising rates. These typically range from 10Hz to 40Hz. Some bluetooth devices have the ability to spoof their MAC address so different advertisements appear to come from different physical devices. This is often important for scalability testing, because some receivers keep track of unique devices by MAC address.
As #Emil says in his answer, it is possible to "interleave" advertisements such that you change the advertisement (and ideally the MAC address) every few hundred milliseconds so it appears by receiving devices that there are multiple advertisers around. I have done this with both Raspberry Pi and iOS transmitters, but in neither case could I alter the MAC address.
It is important to understand, though, that the actual number of packets received when you do this does not change. So while you may be testing scalability of unique advertisements detected, you will not be doing the same thing as testing with multiple physical advertisers.
That's not possible by the Bluetooth specification. However you can start off with one data then set a timer in your app that stops advertising. Then you start off again with the next data. And so on.
Being somewhat of a newbie I was wondering if there is a way to hard-code something on a peripheral that would only allow a single unique central/master to connect.....?
i.e. / eg
I have the ‘simple chat’ Arduino app on a RedBearLab Blend-Micro (which is for all intensive purposes the same as a Arduino Uno with a BLE shield) and I only want one single / unique phone to BE ABLE TO connect with it and therefore work with it.
My understanding is that the GAP handles security features during a BLE connection.
Therefore, is there some way to ‘code’ the peripheral device in / below one of the following includes:
spi.h ?
boards.h ?
EEPROM.h ?
RBL_nRF8001.h (or similar) ?
Other?
Didn't quite get an answer from Restricting the BLE peripheral device to connect to only one Master
OR
Am I stuck with EVERYTHING connecting but coding the peripheral in some other way in a GATT profile (I think) to ONLY do something with a predefined unique central/master (how/where to code?).
Many thanks for thoughts in advance
Being somewhat of a newbie I was wondering if there is a way to hard-code something on a peripheral that would only allow a single unique central/master to connect.....?
Theres the "Advertising Filter Policy" as specified in the Bluetooth Core V4.0 specification. Its a Byte in the Advertising Parameters as specified in Section 7.8.5 LE Set Advertising Parameters Command.
For example the value 0x02 reads Allow Scan Request from Any, Allow Connect Request from White List Only.
Then theres section 7.8.16 LE Add Device To White List Command.
That said, if your device confirms to the Bluetooth 4.0 specification, it should support these HCI commands. However there might be functions that simplify these procedures, wrapping those HCI commands for easier use. Check the Documentation of your device for such methods.
Good Luck!
I was asked to answer this question via email. It's been almost a year since I quit working on BLE. So I only answer this question based on my memories.
Basically #dominik has it right.
If the device is freshly new, it should advertise normally (without setting the whitelist only bit), then any central device could connect and bond. Once it is bonded, you should save this bonded flag and the bonded master's bd_addr to EEPROM. If the next time the master is lost, you will advertise with that white-list-only flag set. If a new central tries to connect, you could verify if its address is the same as your master.
I don't have the BLE spec at hand and I kind of forgot a lot about BLE already. Probably the spec says somewhere that if a central sees a peripheral device is broadcasting with white-list-only flag set, it wouldn't try to connect if it doesn't recognize that peripheral device. This saves both some effort.
But a master could always initiate a connection to your peripheral device regardless the white-list-only flag. So checking if the connecting central device's address is the same as your previously bonded master is the last resort.
[Update]
I used CSR1010 chips. I remembered that the BLE stack actually allows me to insert a list of bd_addr to the white-list data structure maintained by the stack. Then, with the white-list-only flag set, the lower-level stack layer will help you filter devices that are not in that white-list without your knowing.
However, you can always filter bd_addrs from your application code.
Not sure if to posted this on SO.
I'm looking at pretty simple BLE Device. It has a two LEDS (to simplify) that can be switched on or off.
While browsing the GATT profiles, i can't find which profile i should use. Most of them send something back (like a temerature) to the client (upon request).
I need the opposite: switch something on/off of the BLE decive (server). In my case, the client (a iPhone) would send a command to switch on/off LED-1 or LED -2.
What service profile i should use?
Thanks.
I'm using the nRF8001 development kit & nRF Studio for making the services.h
If the LED's are just to be turned on/off there probably isn't any specific profile that they belong to. You probably need to know the handle and write directly to the attribute some value that maps to on or off. Maybe you can figure it out by listing all attribute characteristics. (unfortunately I don't know how to do that specifically on the iPhone)
I noticed that you are using the nRF8001 development kit. So, first thing you need to check is whether the LEDs are connected to IO port of the micro-controller on the kit or directly connected to IO port on BLE chip.
If it connected to micro-controller on the kit then you need to program the kit to handle the received bluetooth data to control led. (It would have a high chance it is in this situation)
If it connected to BLE chip, it means you need to program the ble chip first.
Usually, useful GATT profiles are user specified. It means you need to define the profile yourself. And, I believe some part of the kit or the studio would allow you to do modifications to the profile.
There is only one default GATT profile you should use -- GAP which is to define the defaults like name of the ble device. The others usually are user self-defined profiles.
we want to route the call to ip network instead of GSM network. for that purpose first we are connecting our mobile phone to a PC through bluetooth. So we want to transfer the real time audio data to that PC over bluetooth. Could you please help..
If you can trick the mobile phone to function as a bluetooth headeset [profile] -- which I doubt any phones would support because phones are, well, the consumers of such headset devices -- then you could use it like any other "headset" device. (It would be much more feasible to just purchase a headset or plug in a microphone.)
As far as "where the real time audio data is stored?" -- well, that just won't go anywhere. The "data" (perhaps already in an encoded/delta form) is briefly (like milliseconds!) "stored" in a few small buffers / integrated circuits in the radio circuitry. This circuity will vary based upon phone/radio module used and is not accessible from a PC.
Happy doing productive things.