I was going through this article
Under the heading "Real Time performance constraints" it talks about the constraints and says that "This means that you should not expect to get real-time performance or real-time timing constraints from such programs."
My questions are
What's the solution of this problem in Pi's context. How can we make this a part of the kernel ?
How in other devices, like mobile phones, such interfaces work in real-time.Say the applications and games designed using accelerometer on a mobile phone reacts in real-time .
Answer to your second question: It probably depends on your definition of "real time". I think they mean "there is no guaranteed response time", but in practice the time is "usually finite" - of the order of ms. Which is enough for 99% of applications in gaming etc.
Related
I'd really love to learn to program cheap sensors and modules such as this one:
barometer sensor nRF51822 bluetooth module ibeacon LPS22HB, CR2032 battery holder, specifically to use within iOS and Swift.
I reached out to the company who makes them and tried researching how to get started multiple times, but I really can't figure out where to start. There are also pre-programmed modules, but my interest is programming these cheap ones to fit my needs.
I have the linked module, and a few others, and they appear and can be connected to using beacon detector apps, but display no understandable info.
I'd like to read the barometer pressure reading to start. Help is highly appreciated, I'd love to start working with these.
EDIT/UPDATE: I was able to read the modules manufacture name on one of many iBeacon scanner apps I tried and their name is Yunjia. With this information I am able to find alot more details online about what I have. One website says for these chips I can use LightBlue (the app I used to find the manufacturer name) to modify, read, and write to the module. Any additional advice is welcomed, I'll be researching and testing things out.
I also found the Schematics along with some additional info hidden in the seller website.
Edit 2: I found the manufactures little YouTube channel with some info, looks like I just have to do lots of research and testing and learn everything. https://www.youtube.com/channel/UCvqhWNqDE-v0je0X8XAEF2Q It contains some video instructions.
Edit 3: My short term goal of reading the barometer data was a success! After tons of digging I found I just had to write a value of 0x01 to turn on all sensors, then I was flooded with data and the barometer pressure in bytes which could be translated to the actual amount. Write 0x00 to trun off all sensors.
Apple's iBeacon framework is dirt-simple and very easy to use. It allows you to listen for beacons based a unique UUID, major id, and minor ID. It lets you know when a beacon enters or leaves range, and provides crude (immediate, near, medium, and far) distance values. You can create "beacon regions" that will notify your app when you enter or leave them. That's about it.
If you want to do something like read barometric pressure or temperature readings, you will need to either write your own low-level BLE code or use an existing library. My guess is that these modules are using very standard hardware and that you should be able to find libraries to read their specialized data.
Failing that, you will need specifications on their BLE interface and need to learn how to write Apple Core Bluetooth code. (The link you posted has zero specifications for the units. The only thing it provides is the numbers "nRF51822 bluetooth module ibeacon LPS22HB" (It's not in well-formed English so I don't know how to parse those descriptive terms. I'd google those numbers) Note that Core Bluetooth is a fairly low-level framework and not very easy to learn.
EDIT:
Googling "nRF51822", that is apparently an ARM based chip that includes radio hardware that supports BLE. It sounds like that is a general-purpose chip that vendor would use to build a BLE module. Given that, you'd probably have to reverse-engineer it to figure out how it works.
The "LPS22HB" appears to be a solid state pressure sensor that can be used to build a barometric pressure measurement device. It's no doubt interfaced with the "nRF51822". Without specs you're going to have a very hard time figuring out how it's interfaced however.
I'm developing navigation system for my university as some kind of research activity. I'm using SVGKit to display floor plans. And now I need to provide user locationing service for navigation and tracking. So here's my questions:
1) Do I need some special hardware installed in university (Cisco MSE for example, or some cheaper analogues), or I can apply some software/technologies to our current hardware for server-side user location determining? If I do, what equipment do I need for it? I mean, it would be one unit for the whole university, or one per each floor, or what?
2)
Q: Why doesn't the Redpin iPhone client conform to the iPhone SDK
Agreement? A: Apple does not provide a public API to retrieve WiFi
data. In order to get the iPhone client working we had to use a
private API, which is disallowed by the iPhone SDK Agreement.
(c) http://redpin.org/faq.html Does it mean that RedPin is unacceptable in AppStore, so I can't use it?
3)Does Navizon I.T.S. requires some specific hardware equipment except standart routers?
Thank you all, maybe you can offer me better solutions, I hope. Thanks in advance.
Indoor positioning is a very vast field and many different solutions are available which all use a different combination of hardware/software. Some need no specific hardware to work, others need a very expensive infrastructure to be put in place. In the end, it all depends on the accuracy you are trying to achieve. Here are the most common solutions used, I ordered them by the type of technology used:
Wifi: two main techniques are used here, trilateration and fingerprinting. Both do not require specific hardware if your uni already has deployed access points (APs). Trilateration converts signal strength to distance and then intersect circles (almost exactly like GPS). In general this has poorish accuracy and you need to know the exact position of APs for it to work. Fingerprinting is a pattern matching technique where you first build a wireless map of the environment and then match the measurement against this map.
Bluetooth: same techniques as above can be used with Bluetooth nodes. Of course, there's less Bluetooth nodes than Wifi so you might need to deploy some extra nodes for it to be accurate enough. Same accuracy as Wifi (roughly 5 meters)
Dead reckoning: uses an accelerometer, gyroscope and compass to calculate the speed of heading of the user. Needs to be initialized and calibrated regularly by another absolute positioning technique. Subject to drift so accuracy degrades quickly over time. Upside is its very cheap, no extra hardware or initial survey phase are needed.
UWB: very accurate techniques based on time of flight measurements. Requires expensive hardware for both transmitter and receiver. You can achieve cm accuracy with this but it's probably not what you're after
This is still an field of research so it's not that easy to find something that just works. I suggest contacting the IT department of your university, if they run a Cisco system, I know some of them provide some sort of positioning capabilities but I don't have much details.
As for your iPhone question, any app that accesses the private API to access Wifi measurements will be rejected by the App store, so you won't be able to publish anything that relies on Wifi. You can still use it for research purpose though, you'll just have to figure out the code yourself as there's no official documentation (some unofficial doc is out there though)
Good luck!
I know some basic about iOS programming, now i want to connect my app to another non iphone device e.g. connecting to a bluetooth device that can control a light bulb on and off, or control any furnitures.
My question is, besides iOS xcode, what kind of program i need to learn in order to achieve my goal?
Is there any sources that i can learn from it?
For Bluetooth Low Energy devices, you can use the CoreBluetooth framework to access them.
For Classic Bluetooth devices or accessories that make use of the Dock connector, the protocols are not open, and joining the Made for iPhone (MFi) program is required. I do not suggest this for beginning.
My suggestion is to buy for example a Polar Heart Rate Belt that supports Bluetooth Low Energy. These use standard protocols. Sample code is available from Apple that shows how to read out the heart rate from such a device.
As soon as you have mastered the heart rate monitor example, a next step would be to acquire a programmable Bluetooth Low Energy chip (however, often, the development tools for those are rather expensive!). Those chips can be programmed with custom profiles to listen for Bluetooth Low Energy connections and then performing defined operations (lighting a LED) when writes to characteristics occur. So, you are not limited to heart rate monitors and similar devices.
Keywords that you can search for: GATT protocol, Bluetooth Low Energy, CoreBluetooth.
I know that it's a steep learning curve for beginners, but the area is pretty new. However, I can assure you that it's a fun area.
I also think that you should look in to embedded C programming for the slave device (Heart Rate Monitor)
You could get a tod Smart Beacon Development kit for ~$150 and then use BGScript to code the firmware to control the BLE device from your phone or pc. todhq.com for more info.
I was wondering what amount of time is required to convey information regarding the tilt and position (not gps) of one particular iphone to another. Could 2 iphones send and receive this information simultaneously? What about 3 iphones? I'm interested in an application that is able to simultaneously send and receive and make conditional decisions based on this information received all within a half a second-ish.
Any shot this is possible? If so, is bluetooth or wifi better?
Thanks a ton,
Jake
This is currently not possible without an intermediate server. (Without a jailbreak, which would make it possible, but extremely difficult)
I'm assuming your purpose is gaming, in which case, the latency associated with a trip to a server and back over a cellular data network, is likely to take too long for any satisfactory gaming experience. I don't believe it would be within half a second.
This will be possible via Bluetooth in the upcoming 3.0 iPhone software, but that is still under NDA, so you are not likely to be able to get any reliable performance numbers until it is released. If I were guessing, I would certainly guess that the latency associated with a direct Bluetooth connection would be FAR under half a second.
All you've got as an option right now is Wi-Fi or the Cell Network. If you use Bonjour over Wi-Fi, you'd have latencies in the milliseconds, but all the phones would have to be connected to the same access point. Take a look at the WiTap example.
It is definitely possible, you'd want to connect your peers over WiFi for best performance and reliability, but Bluetooth would be ok as long as your data packets were constrained to small sizes (< 1k). Check out this documentation and sample code to see how to access UIAccelerometer:
http://developer.apple.com/iphone/library/documentation/UIKit/Reference/UIAccelerometer_Class/Reference/UIAccelerometer.html
http://developer.apple.com/iphone/library/samplecode/AccelerometerGraph/index.html#//apple_ref/doc/uid/DTS40007410
The trick is that the update frequency is controlled in part by the systems needs, so there may be a window (while the system is attempting to update device orientation) wherein your application receives no updates.
Does anyone know what kind of range can you get from the iPhone
bluetooth? Also, would the connection be strictly one to one? I know you
can choose from a number of peers to connect to but once the connection
is established, it seems you can only transfer data between one peer? So
basically, is it possible to create some kind of "multiplayer" experience?
Just answering the range part of your question...
The 10 meter figure for class 2 devices (of which the iPhone is an example) is very much a guideline.
The range of a Bluetooth device is limited by many real world factors. The 2.4 GHz radio frequency used by Bluetooth is strongly absorbed by water. For example, consider an iPhone connected to a Bluetooth mono headset. If the headset is in one ear and the iPhone is in your trouser pocket on the opposite side of your body, then there's a lot of water between the two devices. This will often cause a significant amount of packet loss in practice (you can hear this in the audio being carried). So, in this case, the range is about one meter.
At the opposite extreme, two class 2 devices separated by nothing more than clear air can get ranges of hundreds of meters.
Other factors that influence things are:
Interference - Lots of things use 2.4 GHz. WiFi, for example can cause problems.
Antenna design - Space and cost constraints often mean that the antenna design is sub-optimal. I don't know how good the iPhone is in this respect.
Walls - Generally walls attenuate Bluetooth signals. However, sometimes they are useful reflectors.
Quality of hardware - Some chips work better than others. Even different firmware revisions of the same chip may perform differently. Different versions of the iPhone probably have (or will have) different chips in them.
Protocol - It is possible to work around poor signal quality with error correction and retransmission. Even if the iPhone SDK forces you to use a particular protocol, careful design of your application can make a difference.
So, in summary, you should probably do some real world tests.
The connection is one-to-one, but you can create an adhoc network with one of the phones acting as the master/coordinator. The other phones would route all their communication through the master/coordinator.
One device can theoretically connect to 7 devices. according to the master-slave role, the device can multiplex between each of them giving the user an impression that you are connected to all of them simultaneously. Bluetooth specification does not stop you from doing that.This is theory.
Now for the iphone, whether it can connect to to more than one device can only be answered by apple or someone who knows the iphone bluetooth API. But I am pretty sure the bluetooth chip inside iphone should be able to connect to more than one device.
Range is essentially going to be good enough for a normal sized room to be covered. It can be longer or shorter depending on environmental circumstances, but remember that bluetooth was created to implement short range connections.
A bluetooth device can be part of a piconet of eight devices, one master and up to seven slaves. The slaves cannot communicate with each other, they must talk through the master, think of a star topology with the master in the center. The iPhone SDK has a GameKit framework that can be used to create the network for multiplayer games. Go to developer.apple.com at look at the GKTank and GKRocket sample code to see how it's used. These games only support two players, but the GameKit framework supports more. Look at the app store and you will see games that have four or more players.
Hope this helps to get started.
Apple iPhone 3G has a Class 2 bluetooth module. Class 2 Bluetooth devices have a communication range of 10 meters.
At a given instance a device can connect to just one device because it follows a master/slave communication model. But still we can perform a multiplexing. So we can virtually connect to more than 1 device and by rapidly changing the connected device.
I found a good article here. It explains bluetooth very well.
According to the my knowledge, multicasting is not impossible with bluetooth. So gaining a multiplayer experience is NOT impossible.
The bluetooth in the iPhone is Class-2, with a 10-meter range, approximately.
Unfortunately I can't answer the other parts of your question.
One device can be connected up to 8 others. It all depends on the iPhone bluetooth API (which I don't know anything about), but with Bluetooth itself you could then send data to multiple devices.
I tether my iPhone to my laptop over bluetooth every day, and I seem to remember having done that at the same time as using a bluetooth headset. YMMV.
It’s the latest incarnation of Bluetooth, the wireless device-to-device technology that allows your phone to talk to headsets, car stereos, keyboards and other devices directly, without the need for a router or shared wireless network.