Apologise for the probably use of the wrong word in my question but for the life of me I can't think of the right one.
Anyway, I've been playing about with the Bluetooth Low Energy and I'm trying to create something that is going to use the RSSI signal strength the BLE device emits. For this, I need it to emit its pulse multiple times per second.
Is there a way I can up the amount of times my devices either scan for a signal, or broadcast their signal through code on iOS devices?
No, there is no API for you to change the advertisement speed or radio power.
This aspect is fully controlled by the system. You can only start and stop the advertisement and add some metadata to the packets: device local name, advertised services, etc. Moreover, the contents of the advertisement packets will differ depending on whether your app is in the background or foreground and, additionally, in background it will be slowed down. These effects have been documented in various SO questions and in the header files.
If your clients are iOS applications, then they should use either the RSSI in the advertisement packets (centralManager:didDiscoverPeripheral:advertisementData:RSSI: method) or when connected, the readRSSI method on the peripheral object (just make sure you don't call it too often).
Related
I work on iOS application which is using BLE for communication with our custom made BLE unit.
We want to send specific commands via BLE to the unit automatically.
When user is near unit and specific criteria are met, the app should connect to the unit, "login" the user, send command via BLE and disconnect right away.
These specific criteria are based on manufacturer data from advertisement (i.e. the unit is in "available to login" state when manufacturer data has last byte 0x01, when it's "NOT available to login", last byte is 0x00).
In foreground, this mechanism works flawlessly.
We want to do this even when app is in background or terminated (swipe up in dashboard on iPhone).
The mechanism we have implemented:
the unit has capability of acting as iBeacon
when unit is NOT available for login, the iBeacon is OFF
when it IS available for login, the iBeacon will turn ON and wakes up application, upon that the BLE scan will start in background mode
background mode setting is bluetooth-central
Problem here is that no matter what I tried, the advertisement:
sometimes it's not discovered at all (looks like it's timing issue?)
when it's discovered, it does NOT contain manufacturer data
Did anyone come across something similar?
Any help is appreciated and have a nice day!
An app simply cannot read raw BLE manufacturer advertisement data when in the background on iOS -- the operating system prohibits it.
Two exceptions to this rule:
iBeacon, which itself is implemented as a specific type of manufacturer advertisement. An app can detect iBeacons in the background on iOS, although only four bytes of readable data (encoded in the major and minor fields) are fully usable. If you can modify your device to send information this way, it will do what you want. However you must use CoreLocation APIs to detect iBeacon, as CoreBluetooth does not allow reading manufacturer data from iBeacon advertisements. If you do use CoreLocation, you cannot use the detections to establish a Bluetooth connection with CoreBluetooth as the two APIs are sandboxed.
Overflow Area advertisements. Backgrounded iOS apps can read these special types of manufacturer advertisements when in the background but only if the screen is turned on. (It is often possible to force the screen on at specific times by sending a local notification.) See my blog post here for more info: http://www.davidgyoungtech.com/2020/05/07/hacking-the-overflow-area
An alternative to detecting manufacturer advertisements is to use BLE Service advertisements with attached data. For this to work, you'd need to define a 16 bit or 128 bit GATT Service UUID and send out an advert with attached data bytes. Eddystone beacon formats work this way, and allow detection in the background on iOS. This is probably the best approach if you can alter the BLE hardware.
Description - How I can get the number of BLE connection in iOS.
I want to restrict a user to add more BLE sensor after a particular number of BLE connection. I want to get the number of a BLE connection a device can handle.
A connection represents state, not traffic. The count of connections will be bound by either memory or the data structures used by the Bluetooth stack to manage them, both unknown. My answer is, "As many as it can and no more."
Packets represent traffic and each is handled one at a time. From this perspective, my answer is, "One."
However, if a packet cannot be processed out of the critical paths in the chip and protocol stack fast enough to begin processing the next packet, packets can be dropped. Experience has shown these critical paths in iOS are dependent on the traffic's packet size and rate. Additionally, other devices in the area not connected to your BLE stack may be flooding the radio spectrum and causing packet collisions outside the stack. I have seen BLE traffic go to hell with an excess of 20 connections and as few as one. From this perspective my answer is, "It depends."
Is it possible to send only 1 iBeacon packet? I have tried using CBPeripheralManager,but since there are only 2 method to start and stop advertising, so I can't control how many packet is being broadcast.
What I want to try to do is use an iBeacon packet as a command, instead of just a broadcasting some ID. So I could send 1 iBeacon packet, and if the receiver got the message, it can send back Acknowledgement with another iBeacon packet. The intention is to avoid the pairing of bluetooth to send very simple data. The information will be linked to UUID, major, and minor of the packet.
Or are there better ways to do this than using iBeacon.
Yes, you can use iBeacon technology to send information back and forth between two iOS devices without pairing. If you have two devices, Device A and Device B, you set both of them up to range for beacons with a common ProximityUUID, say, E2C56DB5-DFFB-48D2-B060-D0F5A71096E0. And then you can exchange information in the two byte major and minor fields.
What you can't do is control the transmitter enough to send only a single iBeacon advertisement. The transmitter in iOS sends out 10 advertisement packets per second, so the best you could do is start the transmitter then stop it on a timer about 100ms later. (You probably shouldn't do this, because there is no guarantee that a single iBeacon advertising packet will be received successfully by the other device -- it may be lost due to a CRC error in the radio noise. You are probably better off letting the packet continue to transmit until you can confirm from a response from the other device that it was received.)
You can see an example of starting and stopping a transmitter on a timer in my answer here.
Of course, there may be easier and more robust ways of accomplishing what you want with built-in Bluetooth data exchange mechanisms. But that doesn't change the fact that what you propose is certainly possible.
No you can't since iBeacon is uni-direction device
I want to build and app which can detect other iPhones with my app within 65 feet range. As I understand I have the following choices:
Use Bluetooth to check periodically whether there is device with my app in the range. Send list of found devices to the server. The problem here is battery consumption. Is it true that Bluetooth will be disabled after some period of time automatically?
Can I use BLE technology for this purpose? If so, do you know what devices support BLE?
What is the best option on your opinion? Did I miss some other option?
Thanks
UPDATE
I plan to run search every 20 seconds or even more often.
There is no simple answer to this problem.
Bluetooth has 2 flavors: "Regular" bluetooth, used for hands-free devices, headphones, and the like, and BLE (Bluetooth Low Energy)
Regular bluetooth devices must be paired. (I'm less familiar with regular bluetooth than BLE, so take my explanation of this bit with a grain of salt.) In order to be paired they have to be put into "discoverable" mode, which broadcasts their ID. That is a battery-draining and only done briefly. It's not an "always on" solution.
BLE has a range of up to 60 meters, so it should meet your need in that regard.
BLE devices can "advertise" as a "peripheral" for extended periods. Other Bluetooth devices can act as a "central" and ask to be notified when certain peripheral devices are detected. I'm not sure if you can make an iOS device advertise (broadcast) as a BLE peripheral while it's in the background and/or if the device is locked, but it will certainly advertise while it's running. I'm pretty sure you can register to be notified when you detect a certain BLE peripheral from the background, but not positive.
iBeacons are a specific use of BLE with some extra limitations and some extra abilities. An iBeacon is a dirt-simple transmitter that sends a UUID plus a major and minor value and a signal strength calibration value periodically (usually once a second.) You can't add any other data to an iBeacon transmission. iOS can only act as an iBeacon transmitter when the app is in the foreground. If your app moves to the background, it stops transmitting. Period.
However, you can listen for iBeacon signals even from the background. AND, if you've registered as a listener for an iBeacon and the system terminates your app due to low memory, the system still listens for those beacons on your behalf. If iOS detects a beacon you're listening for, you get re-launched if needed, and notified in the background. You can then post a local notification to get the user's attention.
iBeacons are probably your best bet, but you will need your users to be actively running your app in the foreground in order to transmit a signal. That will drain your user's battery fairly quickly.
One possible solution would to have have every single device send their locations to your server every predetermined time period (more frequent the better but more resource intensive). Then, query the data from the server and get the location of all the devices near you.
Keep in mind, that this probably won't be very useful for real-time data collection. For example, if you want to send data every 30 seconds or so, this isn't a good option.
Use this option if you want to get data every 15-20 minutes or so.
I want to know in regards to iOS what is the typical advertising rate for peripherals running in the background. I know that it will vary depending on what you are doing in the foreground , but I do not know to what degree. I have read it changes only by 10's of ms but then i have also read it can change by up to 4 seconds between advertisement packets. I can fit all of my data needed into 1 packet. I would like to know between advertising this one packet in the background and nominal iphone usage how likely is it that my advertising rate will still be in the ms range?
Also i have read that i can change this interval programatically, but the examples are only for 30 seconds. (im guessing due to limited discoverability mode?) Is there a way I could keep recalling this advertising boost? OR Maybe I could start as a central scanning in the background instead and when i scan a certain packet i could switch to peripheral mode (since you can only do one or the other in the background) and my advertising boost could happen then. Then when that thirty second boost is over i could switch back to central mode until i scan that certain packet again right? This way i would only have a small window of poor advertising rate every 30 seconds. Is that probable?