This may look pretty straight forward, but I have googled, stack overflowed and searched Android Developer guide as well.
How can I access the Hall sensor present in the phone? I know my phone has one and programmatic access is possible (it came with a Flip cover that worked on the Stock ROM). I'm trying to extend that functionality to AEX custom ROM.
I've played around with various sensors present in the Sensor class (android.hardware.Sensor) - but couldn't find the Hall sensor among it.
So my question - Is High level programmatic access to it is possible, or is it something like Kernel-only, or is there any third party API?
Of course, I know I could instead use a Proximity sensor - but accessing Hall sensor should be simple, right? What obvious thing am I missing?
Isn't it just a magnetic field that you want to detect? Wouldn't a Magnetometer give the values you need.
Maybe physical sensor does not exist but a composite one does, i.e. something that will allow you to determine values based on a collection of values from other sensors.
In this case other sensors could be the Position Sensors
for example you could get a reading on the magnetic field strength and orientation to perhaps get the value you need.
Related
I would like to make an app which is keep tracking various points in a room in 3D and can tell where to look up the tracked points again.
The problem is: I can't use GPS and Wifi points to determine my phone's location and orientation.
So far I know two things which can be useful in this case, the gravitation force, and magnetic north. It is not a problem if there is some misleading fake magnetic north unless it is too close to the room where I want to locate things.
I found that the gyro + acceleration isn't accurate enough to use, is there a "ready made" API what I can use for that? I have the feeling I am reinventing the wheel.
Thanks in advance.
There is only one "ready made" API - Fused locations ( https://developer.android.com/google/play-services/location.html ). But currently it relies on GPS/WiFi/Cell-tower data. I don't beleive there is easy/cheap solution for your problem.
You could use bunch of Bluetooth devices, maybe some BT4 low power tags. Place them everywhere in the room and measure signal strength of each.
I am trying to determine the benefit of making use of Android's Linear Acceleration data as opposed to simply applying a low pass filter as presented in Androids API reference and discussed in this other stackoverflow question.
I am asking as I am trying to get hold of a free app that records Linear Acceleration (as well as fullfils my other requirements (sampling rate, writing data to file etc...)). I haven't been able to find one, so I have considered just using an app that records using the standard accelerometer and then I'll simply apply the low pass filter to the data. Alternatively I could just write my own app to do what I need - but I don't have much experience in Android dev and this will take some time.
I have explored this subject at some length and I may be able to help point you in the right direction.
As others have mentioned, only some phones have implemented TYPE_LINEAR_ACCELERATION and TYPE_GRAVITY and they usually are equipped with a gyroscope. A Droid Razr even has a gyroscope, but they never bothered to implement it or TYPE_LINEAR_ACCELERATION. I believe the GS2 has TYPE_LINEAR_ACCELERATION implemented, but no gyroscope so they must have used the magnetic sensor or some sort of low-pass filter. It can be frustrating.
On most phones with a gyroscope there is some sort of fusion between the acceleration sensor and gyroscope (probably a complementary filter to compensate for drift and then quaternions or cardan angles to isolate gravity). These fusions and filters can be implemented differently and use different hardware, etc... Latency and accuracy are going to vary among devices, so TYPE_LINEAR_ACCELERATION isn't always going to produce the same results.
If you do not have a phone with TYPE_LINEAR_ACCELERATION, you are stuck with TYPE_ACCELERATION, which cannot separate gravity (tilt) from linear acceleration.
One option is to apply the low-pass filter. This may or may not work depending on your application. I have written a free application to help developers and other interested parties explore the low-pass filter option.
Another option is to just measure the tilt of the device when it is static and then apply that gravity measurement while the device is not static. If the device isn't changing the orientation often, this can be an excellent option because it is really fast and simple.
An excellent alternative sensor fusion option is to use the magnetic sensor instead of a gyroscope. This option will work on almost all devices assuming the magnetic field isn't under the effects of hard or soft iron distortions.
I have implemented all of these approaches in the open source project Acceleration Explorer
I'm working with android sensor data. My application use
SensorManager.getRotationMatrixFromVector(
mRotationMatrix , event.values);
and it has been working well until this morning, when the rotation matrix started to send a lot of noise data (Change N to W in a second).
It's not a problem with my code, because on friday was working and no changes have been done. I have used a compass app from the market, and the compass is giving random data.
I have tested my app on another tablet, and it is working well.
Does someone know why is this happening? A problem with the sensor? Does it need a calibration?
I've worked quite a lot with these electronic compasses on mobile phones and its quite possible that there is nothing wrong with your code or sensor.
Instead it could very well be a problem with your environment. There are magnetic fields interfering with the earth's magnetic fields all the time. From electrical equipment interference to the metal structure holding up a building. At the end of the day a compass is just a magnet. If you stand beside a large lump of metal the compass will be attracted to it and point to it rather than the magnetic north pole.
Try this:
Install GPS status
then turn off all filtering (settings... gps & sensors...sensor filtering... no filtering).
Do the calibration (figure of 8 wavy stuff) and then move the phone around your desk.. near monitors, cables, etc. You'll see it go crazy. The information is completely unreliable. I found in the past that moving the phone a few inches to the right completely changed its reading. The same happens with a real compass. Strictly speaking there is no "problem". The device's compass is assigning itself with the strongest magnetic field. Even the magnetic content of nearby rocks can interfere with the compass.
As a further test I've just placed a real (orienteering) compass over my phone which has a compass app installed. The real compass is now pointing everywhere but magnetic North. The two devices are interfering with each other.
So my advice is.. go somewhere in the open, like a park or field, away from any potential interference and power lines, (if you have one bring a real compass to check that the GPS status app is pointing the right way), and see if your compass works as you'd expect.
Extra: The answer from #resus is also important when calibrating. Rotate the phone a few times in each axis. Looks silly but it does calibrate it properly.
Extra 2: Would it be possible/practical to use the compass bearing of your GPS? It would require that the device be moving (walking speed should be fine) but you would not need to worry about any interference. It should give an accurate reading provided your GPS signal is good.
Extra 3: Another thought just occurred to me.. You could try apply a low pass filter to the sensor. This means that the sudden changes in the sensor reading are filtered out .. have a look at this answer. And if that doesn't do a good job there are lots of algorithms on the web for you to choose from.
If you definitely haven't changed anything in your code, and it still works fine on other devices, it would suggest a problem with that particular device.
While your app is running (i.e. the compass is in use), you should be able to wave it in a figure of 8 in order to automatically recalibrate the compass. You should also make sure you aren't standing next to any large lumps of metal etc. that might interfere with readings.
You can override the onAccuracyChanged() method of SensorEventListener to flash up a message to the user when the compass requires recalibration (probably when accuracy drops to SENSOR_STATUS_ACCURACY_LOW).
In my experience of playing with the compass on android phones, they can be pretty unreliable...
If your application work on another tablet and other compass application do not work on your device, this is probably due to a bad calibration.
As said in the post above, to make the calibration, wave your device in a figure of 8. I just want to add that you should do it for EACH axis. This should fix your problem.
If it is not a calibration error, as some people have already answered, it is possible that the compass had gone through a magnetic field and now it is desmagnetized, so it is not working properly.
Where do you usually keep the tablet? Could it be that it was near big servers or magnets?
You should check the compass just in case, talk to to android's tech support.
Hope it helps.
I think the question was if calibration could be done without sending any data to compass. Because not everybody says that the compass is calibrated as shown in this video: https://support.google.com/maps/answer/6145351?hl=en and obviously you can not do anything else than advise the user to calibrate before using the program or when you get too much changes.
For example going left and right 90 degrees in about 25 ms.
Anyway I think it's good to give some seconds to the app before start taking data, because it gives some unstable values (too high and low in short time without movement) at the app loading moment.
Just let the handler onSensorChanged() coded with a conditional, and start a thread on the onCreate() handler, which will set a boolean to true, after some seconds.
Then you start to capture data on the onSensorChanged() handler.
Also this thread can help to detect the sensor accuracy, and then you can popup: In Android can I programmatically detect that the compass is not yet calibrated?
I know because I am building a robot using the compass of the smartphone, and I'm having this experience. So, if you are making a robot, make sure to give an spaced place between electronics and hardware to the smartphone, but remember that it's on any compass: electromagnetic fields can be altered by metals so heavily.
Nowadays I have the luck of developing a robot with an HMC-5983 and an MPU-6050, which can be calibrated by using its libraries with Arduino.
That code is compatible/portable to other uController but for not also so easy for smartphones, I guess that the offsets needed for calibrating the compass, the gyro and the accelerometer are inside some internals of Android, not available in the SDK.
I answered before thinking that maybe calibration was only for some devices, but realized that must be as I said before.
So, if playing with robots its possible, I mean it's also easy, but when using an smartphone maybe some custom firmware as CyanogenMod would bring the possibility of investigating the way of setting that offsets, but more important to run some program ported from sketch (following its concept only) to get them first ...
So, good luck ! What is also true, is that in both devices (smartphone and my robot) it's need to move them for them to get working well, as I showed you in the video of latest answer, also helpful on robots.
Good luck and a lot of fun with those things, are very powerful.
is there a way to root my Android phone and get sensorinformation direct from the sensor or system?
LG marcel
I don't really know what you mean by getting the information in a "direct" way.
There are two types of sensors in the android sdk: sensors representing an actual hardware sensor (e.g Sensor.TYPE_ACCELEROMETER) and virtual sensors like Sensor.TYPE_LINEAR_ACCELERATION which values are calculated based on the data of one or more sensors. Using the sensor types which represent real hardware allows you to read the data delivered from the sensor The problem with all kind of sensors in smartphones today is that there might be some kind of preprocessing (e.g lowpass filtering) involved and there is little documentation on where and how this is done as there is often no information on which sensor is used the device. I recommend reading this article on android sensors.
Hope this helps...
In android, you have the SensorManager class which give you the possibility to work with your sensors on the device (except the GPS and the camera sensor).
To understand how it works, see this:
http://developer.android.com/reference/android/hardware/SensorManager.html
If you have questions abaut this, feel fre to post them.
I'm making an application that works as a compass..
I'm using the accelerometer and the magnetic field sensors to compute the azimuth angle through, sensor.getOrientation().
I'm searching for something that can improve the magnetic field sensor accuracy, since I'm getting it state of accuracy as UNRELIABLE!
Any one knows anything about this?I'm looking for something that can be either hardcoded or for instance just physically moving the phone until it gets calibrated!
This is not a final answer (I don't know anything for sure), but my understanding from online posts is that waving the phone around in a figure of 8 a few times while the compass is in use is supposed to trigger automatic recalibration. This is what the google maps app suggests, for example. I don't know whether this is dependent on application functionality (something in maps that detects the waving by accelerometer and triggers a recalibration), or something in the android stack, or something specific to per-phone implementations. Try it and see!
Eg discussion: http://androidforums.com/epic-4g-support-troubleshooting/217317-cant-get-compass-calibrate.html
This reference appears to suggest this per-axis / figure-8 rotation process is built-in functionality: http://m.eclipsim.com/gpsstatus/
And here another article that claims this is built-in functionality, and that you don't even need to be running a compass-consuming app for the recalibration to work: http://www.ichimusai.org/2009/06/20/how-to-calibrate-the-htc-magic-compass/
Just a few points
The figure 8 motion works sometimes and not others, I have no idea why, they really need to have some kind of code based way to check if the 8 motion worked (Assuming that the physical motion is actually required)
They also need a way to detect that calibration is required, I looked at the code for the accuracy output (the unreliable constant) and once they send it to you they will not send it again, so for instance if you calibrate but then come within a strong magnetic field it will not resend (not sure why they did that)
One not completely reliable way to detect ongoing issues is that you can also use the magnetic sensor output and do something like field=sqrt(x*x+y*y+z*z) and check that field falls between say 25 and 65 and then ask the user to calibrate if it does not.
The bottom line after testing 18 phones is that I would never depend on a Android based compass with the current crop of phones, accuracy would always be in question.
I have also found even if you are lucky and have a fairly reliable phone you can never be sure that it's calibrated without checking it against a real compass, which kind of defeats the purpose.
NOTE: On a lot of the mis-behaving phones we have found that the sensor writes a calibration file and a tmp file with the same name. If you delete those files and re-boot the phones the calibration file is recreated with zero'd values and the cold start and general calibration problems resolve themselves.
The bad news is that they are stored in /data/misc and require root privileges to get at (thanks Google & Sensor mfg!) so even though I suspect this would solve a lot of problems for a lot of developers it just is not viable from a marketplace app perspective.
I am developing for Android. I'm using Titanium Alloy as development tool with the Titanium Geolocation module.
I have only tested 2 devices [Galaxy Note and S4] against a commercial magnetic compass. Following a calibration process [tilt along the 3 axis] and using 2 different compass apps and the app I'm working on, the Android compass seems accurate enough for basic use ... correlation was good enough for my purpose anyway. I also found the device compass reading to be very sensitive to other magnetic and electrical field interference ... initial mistake I made was to use the compass feature whilst device was in a device protector with a magnetic closure facility [quite common on tabs] ... this interference is particularly strong. I thus need to suggest to users of my app to remove device protectors, keep device free of other electronics and then do standard calibration before initializing the app.
Another option is:
Go To sensors menu: #*0#*
Then if you see a red line in Magnetic Sensor section and a Need for Calibration you should recalibrate your compass.
How;
According those guys;
Turn the Samsung Galaxy Mini S5 around all of its axes until the red
line in the black circle changes color from red to blue. You can also
run through a motion that follows the shape of an 8. It may be that
several attempts are needed to calibrate the compass...