Let's say I want to start transmitting advertising packets from a Blueooth 4 module attached to a Raspberry Pi. I am planning to use BlueZ library for the same. Have a basic questions regarding the same -
How much memory does a typical Bluetooth device contains (is it standard or something that can change from vendor to vendor) ? In both the cases, does the advertisement has to be 27 bytes (iBeacon) and 28 bytes (Altbeacon and URIBeacon) or can it be extended to any number limited by bluetooth memory size or any other guidelines? Wish to understand a little bit about this topic.
Thanks in advance!
Device memory is not what limits the Bluetooth LE advertisement size. The limitation is imposed by the Bluetooth 4.0 Core specification, which allows for a maximum of 28 bytes in a manufacturer advertisement PDU (including the one-byte PDU length field).
While you can't transmit more data in a single advertisement, it is possible to send more data using other techniques including:
Interleaving multiple advertisements from the same transmitter. You can differentiate these advertisements with a "type" byte, and then use this to stitch them together with the receiving device. Disadvantage: complex implementation.
Using a scan response packet to send additional data. Disadvantage: scan responses may not arrive in a timely manner.
Provide a connectable GATT service that can be used to fetch additional data. Disadvantage: once connected, advertising stops.
Use a web service to look up additional data based on a unique identifier in the advertisement. Disadvantage: It won't work with out an internet connection.
Related
I have a question regarding BLE. It's my first time trying to use BLE and I am exploring some high level designs for a medical device. The structure would be that the device connects to a stand alone controller-device (wifi disabled) via BLE. The device would be collecting data such as heart rate throughout a 24 hour period. At some point the stand alone controller would be disconnected from the device and connected to an app to transfer the data collected. Can BLE handle the potential data size of this scenario? Is it fast enough to do it in a reasonable amount of time?
Thank you!
Take a look at the specification list provided by the Bluetooth SIG. Two documents describe the handling of heart rate measurements, the most interesting for you would be the Heart Rate Service specification (Download it here: https://www.bluetooth.com/specifications/specs/heart-rate-service-1-0/).
It contains a detailed description on how to transmit heart rate data via BLE. According to the specification you are supposed to use the 16-bit UUID 0x180Dfor the Heart Rate Service. You can find the UUIDs for other services and characteristics in the 16-bit UUID Numbers Document.
I need to advertise 2 different sets of data, 31 bytes each. It doesn't look possible when I look at the core specification v4.0.
What I understand when looking a bit further, beacons can be advertised in 3 different channels : 37, 38, 39. LE Set Advertising Parameters Command makes it possible to choose a specific channel as well as all at once.
Is it possible to advertise different data in different channels ?
If it is not possible, the only solution I remain with is changing the advertisement data periodically using LE Set Advertising Data Command.
I would be glad to see a bit insight on performance, stability and power consumption.
Yes, your device can act as several BLE beacons as long as you periodically change the advertising payload. Your suggestion of using LE Set Advertising Data Command is my recommended approach and you don't need to change the advertising channel for this purpose.
In other words, what you can do on your device is set up a timer, and then as soon as the timer expires, you can switch to a different set of BLE data that is being advertised, which will create the affect of your device acting as multiple beacons.
Please see the following links which may be helpful to your question as well:-
Can BLE devices act as beacons
advertise custom service uuid with bluez 5.4x
Linux BlueZ custom Manufacturing Scan Response Data
Bluez BLE peripheral advertise custom characteristic with ADV data
I hope this helps.
I have a small BLE beacon which is configured to send iBeacon packets every 1000ms.
In my usecase i want to detect the signal on multiple recievers every time it is sent. However the detection is not reliable no matter which receiving device and software i use (phone, computer, raspberry). The signal is sometimes detected after 2 seconds, another time 5, 6 or whatever. It seems like there is no pattern behind it.
Also it seems that sometimes the signal is received on one receiver but not on the others while definetly being in range! Also the area i am testing in is not "problematic".
What could be the problem?
Not 100% of beacon packets transmitted are ever received. There are a number of reasons for this, including radio noise, packet collisions and channel hopping. That said, the typical detection rate in a quiet radio environment is around 90 percent.
If you are seeing a much lower rate than this on multiple receivers I would check the transmitter. First, use one of.your devices to transmit a software beacon (Android and iOS have free apps like Locate Beacon that do this.) If you get a higher detection rate with a different device transmitting, the issue may be your transmitter.
A few possible issues with it:
Bad antenna sending out a very weak signal. (Measure the received RSSI when you do get a detection and verify it is over -60 dBm)
Weak transmitter power setting. See if you can configure this higher.
Advertising on wrong channels
Advertising is stopped before packet can go out. Try to leave the advertiser on for at least 2x the transmission rate to ensure at least on packet gets out.
I assume you use a large enough scan window for your scan interval so your receiver radio is actually turned on most of the time.
You could try to send advertising packets of the type ADV_NONCONN_IND (non-connectable and no scan response packet). That way if the receiver radio scans with 100% duty it should see the packet.
Otherwise if you use normal ADV_IND packets, then at least Android always waits for the SCAN_RSP packet before it sends anything to the scanning app. But if the are multiple scanners nearby, your peripheral can only respond to a single scanner's SCAN_REQ for each advertising packet. To avoid collisions of SCAN_REQ packets in the air, Bluetooth controllers also back off if they don't get a SCAN_RSP in return. If you use a BLE sniffer you can see all three kinds of packets and what happens when you have multiple scanners nearby.
Read the BLE Link Layer part of the Bluetooth Core specification for more details.
I couldn't find a clear explanation what is Bluetooth le multi advertising.
For example, in Specification of the Bluetooth System, I see only
description of BLE advertising but not multi advertising.
What the difference between BLE advertising and multi advertising?
Thanks
LE Multi advertising refers to a specific offload (non bluetooth specification) feature that has been implemented in the Android releases by Google, starting from the L release.
What multi advertising means is, that your Android phone or a device with Android stack, can enable multiple advertisement trains at the same time. For instance, one specific app can set certain advertisement data (example supported services etc.), advertisement parameters and enable advertisement, and so can N number of other apps, on the same device.
At the hardware level (or physical layer), these advertisement trains are interleaved between the three advertisement channels (37, 38, 39) and thus your phone behaves as multiple peripheral devices at the same time. All these advertisement trains also have a separate Random private address, so they are seen distinctly by the remote scanner.
Bluetooth Smart has two ways of communicating. The first one is using advertisements, where a BLE peripheral device broadcasts packets to every device around it. The receiving device can then act on this information or connect to receive more information. The second way to communicate is to receive packets using a connection, where both the peripheral and central send packets. We will focus on advertisement for several reasons:
You can’t create a connection between two devices without using advertisements. Defining the data and format of advertisement packets is usually the first thing you work on when developing a BLE device.
A large number of BLE products sleep most of the time, waking up only to advertise and connect when needed. This means advertisements have a big impact on power consumption.
Users want responsive products, and the advertising interval is critical in quick connections.
Advertising is by design unidirectional. A Central device can’t send any data to the Peripheral device without a connection. But a single peripheral can advertise to multiple masters in the area.
ref:http://www.argenox.com/bluetooth-low-energy-ble-v4-0-development/library/a-ble-advertising-primer/
As a 3rd party is there a viable way to correctly interpret data from a Bluetooth Low Energy device for which there is not a published GATT profile specification?
The BLE device is a body scale that supports weight, BMI, body fat, and hydration level. My understanding is that there is no adopted GATT profile for body scales like there are for, say, blood pressure devices or heart rate monitors (https://developer.bluetooth.org/gatt/profiles/Pages/ProfilesHome.aspx).
Using the following tools:
iPod (iOS 6.1.3) with various BLE utility apps (Ti BLE Multitool, LightBlue, and BLE Utility)
Android (4.3) tablet (Dell Venue 8 3830) with nRF Master Control Panel, plus a custom Xamarin developed solution
I can scan for, locate, connect to, and read the GATT services available on the scale. All of the above tools give me the same service information. There are 5 services discovered on the scale:
Generic Access (0x1800)
Generic Attribute (0x1801)
Device Information (0x180A)
Battery Service (0x180F)
An unknown service with a custom 128-bit UUID
All of the above tools are able to read from the known services, like retrieving the battery information or the device name. My assumption is that the unknown service with the custom UUID is the service that provides the scale data.
This service has 5 unknown characteristics with custom UUIDs:
Characteristic 1 is Read/Write
Characteristic 2 is Read
Characteristic 3 is Read/Write
Characteristic 4 is Notify
Characteristic 5 is Read
Using the tools that were specified above to read from characteristics 1, 2, and 3, each returns it's own value, but that value never changes. For example, a read of characteristic 1 always returns a value of 20 octets 0x01-0x05-0x06-0x07-0x08-and 15 0x00 octets. Subsequent reads of characteristic 1 always return that value. Characteristic 2 reads always return a value of 20 octets 0x02-and 19 0x00 octets. And so on.
Reading characteristic 5 appears to either not return a value, or more commonly on Android, issue a pairing request. No common pairing code (like 0000 or 1234, etc.) is valid.
Characteristic 4 appears to be what actually transmits the scale data. Using the tools above I can enable notifications and the applications retrieve 13 octets. For example:
FF-16-09-00-03-04-01-00-83-6F-F4-18-0F
FF-16-09-00-03-04-01-00-3E-88-F4-18-E3
FF-16-09-00-03-04-01-00-C8-89-F4-18-6E
Obviously all of those values begin with the same set of octets. The main problem though is what do those octets represent and how do they translate to weight/bmi/hydration/body fat values, if in fact they do at all.
The scale is built with the Ti CC2541 chip (http://www.ti.com/product/cc2541).
Using Ti's SmartRF Protocol Packet Sniffer along with the CC2540 USB Evaluation Module Kit I can capture packets going between an iPhone 5S (iOS 7.1) and the scale. This has provided some additional insight, but mostly just shows what I've already observed using the other tools, though albeit it at a lower level. Any additional information provided by the packet sniffer still leads back to the same question: what do these sets of octets the scale is sending represent and how do they translate to weight/bmi/etc? I've utilized the Bluetooth Core Specification documentation and that has helped to understand what octets for standard functionality mean/do, but that isn't helping understand the actual scale data.
I'm very new to Bluetooth development and this exercise has basically resulted in a crash course in the technology. Any help is appreciated.
Thanks.
You must contact the manufacturer and ask for clarification about the custom service and characteristics.
Characteristic 5 seems to have higher security settings, hence why it triggers pairing when you try to read it. Most likely contains some sensitive data.
Characteristics 1,2,3 are likely for configuration, while 4 notifies the useful data.
Since these are all custom, there's simply no way to find out what they mean without information from the manufacturer.
It's like you create your own "We're out of yogurt" notification profile... one can only guess by looking at the data.