Thingy 52: Motion sensor (accelerometer) raw data in IOS is giving unit vector, I was expecting more of a m/s2 values. Is my assumption wrong?

RE: Thingy 52: Motion sensor (accelerometer) raw data in IOS is giving unit vector, I was expecting more of a m/s2 values. Is my assumption wrong?

Carl Richard — Tue, 01 Sep 2020 09:22:01 GMT

Hello!

I am not sure why this is, but I guess is down to developer preference. To be sure that the conversion results are the same for both applications I recommend doing an output comparison if possible. For you info the values are encoded in the Q number format.

Best regards,
Carl Richard

RE: Thingy 52: Motion sensor (accelerometer) raw data in IOS is giving unit vector, I was expecting more of a m/s2 values. Is my assumption wrong?

Prabhakar_katlakunta — Mon, 31 Aug 2020 15:17:46 GMT

Hi Carl,

Thanks for the update.

I have seen below code for Android

final float mAccelerometerX = (float) (characteristic.getIntValue(BluetoothGattCharacteristic.FORMAT_SINT16, 0)) / (1 << 10);

final float mAccelerometerY = (float) (characteristic.getIntValue(BluetoothGattCharacteristic.FORMAT_SINT16, 2)) / (1 << 10);

final float mAccelerometerZ = (float) (characteristic.getIntValue(BluetoothGattCharacteristic.FORMAT_SINT16, 4)) / (1 << 10);

And for IOS below is the code

accelerometerData.append(Float(rawData.asValue(offset: 0) as UInt16) / Float(2 << 14))

accelerometerData.append(Float(rawData.asValue(offset: 2) as UInt16) / Float(2 << 14))

accelerometerData.append(Float(rawData.asValue(offset: 4) as UInt16) / Float(2 << 14))

For android signed int is considered and for IOS it is unsignedINT. Please help me in understanding this part because I have to build the app for both IOS and Android. And if you notice the bit shifting is also different for both of the platforms.

Regards,

K.Prabhakar

RE: Thingy 52: Motion sensor (accelerometer) raw data in IOS is giving unit vector, I was expecting more of a m/s2 values. Is my assumption wrong?

Carl Richard — Mon, 31 Aug 2020 06:56:24 GMT

Hello again!

My apologies. I mixed up my unit conversion. You should multiply by 9.8. Hopefully that will result in correct values.

Best regards,
Carl Richard

RE: Thingy 52: Motion sensor (accelerometer) raw data in IOS is giving unit vector, I was expecting more of a m/s2 values. Is my assumption wrong?

Prabhakar_katlakunta — Mon, 31 Aug 2020 04:41:05 GMT

Hi Carl,

Solving this problem is important to me. Request you to help.

Thanks & Regards,

K.Prabhakar

RE: Thingy 52: Motion sensor (accelerometer) raw data in IOS is giving unit vector, I was expecting more of a m/s2 values. Is my assumption wrong?

Prabhakar_katlakunta — Fri, 28 Aug 2020 06:46:57 GMT

Hi Carl,

I have implemented as you suggested. Below is my code

peripheral.beginRawDataUpdates(withCompletoinHandler: { (success) -> (Void) in

NSLog("Raw Data Update")

}) { (acc, gyro, compose) -> (Void) in

var trimmedX = (acc[0] - 2.0)/9.8

var trimmedY = (acc[1] - 2.0)/9.8

var trimmedZ = (acc[2] - 2.0)/9.8

if abs(trimmedX) < 0.05 {

trimmedX = 0.0

}

if abs(trimmedY) < 0.05 {

trimmedY = 0.0

}

if abs(trimmedZ) < 0.05 {

trimmedZ = 0.0

}

NSLog("trimmed X: \(trimmedX), Y: \(trimmedY), Z:\(trimmedZ)")

}

But I didn't see the output I was expecting. Please find the log below while I was shaking the device.

2020-08-28 12:12:25.971478+0530 TestThingy[706:49448] trimmed X: -0.2040754, Y: 0.0, Z:-0.20095825

2020-08-28 12:12:26.061594+0530 TestThingy[706:49448] trimmed X: -0.20329377, Y: -0.20396952, Z:-0.20080255

2020-08-28 12:12:26.181168+0530 TestThingy[706:49448] trimmed X: -0.20334049, Y: -0.20303842, Z:-0.19916767

2020-08-28 12:12:26.271155+0530 TestThingy[706:49448] trimmed X: 0.0, Y: 0.0, Z:-0.2011451

2020-08-28 12:12:26.361205+0530 TestThingy[706:49448] trimmed X: -0.20364878, Y: 0.0, Z:-0.20216027

2020-08-28 12:12:26.481102+0530 TestThingy[706:49448] trimmed X: -0.19780372, Y: -0.20232843, Z:-0.20008631

2020-08-28 12:12:26.571227+0530 TestThingy[706:49448] trimmed X: -0.19770408, Y: -0.19878154, Z:-0.20184264

2020-08-28 12:12:26.661201+0530 TestThingy[706:49448] trimmed X: -0.19885628, Y: -0.20355847, Z:-0.19991817

2020-08-28 12:12:26.781093+0530 TestThingy[706:49448] trimmed X: -0.20280176, Y: 0.0, Z:-0.20059702

2020-08-28 12:12:26.871109+0530 TestThingy[706:49448] trimmed X: 0.0, Y: 0.0, Z:-0.20178658

2020-08-28 12:12:26.991072+0530 TestThingy[706:49448] trimmed X: -0.20233466, Y: 0.0, Z:-0.19944483

2020-08-28 12:12:27.081696+0530 TestThingy[706:49448] trimmed X: -0.19770408, Y: -0.20360518, Z:-0.19858535

2020-08-28 12:12:27.171119+0530 TestThingy[706:49448] trimmed X: -0.19770408, Y: -0.19770408, Z:-0.19949153

2020-08-28 12:12:27.261592+0530 TestThingy[706:49448] trimmed X: -0.1988656, Y: 0.0, Z:-0.20040706

2020-08-28 12:12:27.381122+0530 TestThingy[706:49448] trimmed X: 0.0, Y: 0.0, Z:-0.20167136

2020-08-28 12:12:27.471149+0530 TestThingy[706:49448] trimmed X: 0.0, Y: 0.0, Z:-0.20258689

2020-08-28 12:12:27.561099+0530 TestThingy[706:49448] trimmed X: -0.19964412, Y: -0.19770408, Z:-0.19770408

2020-08-28 12:12:27.681090+0530 TestThingy[706:49448] trimmed X: -0.2024561, Y: -0.20305088, Z:-0.20010188

2020-08-28 12:12:27.771100+0530 TestThingy[706:49448] trimmed X: 0.0, Y: 0.0, Z:-0.20204194

2020-08-28 12:12:27.980452+0530 TestThingy[706:49448] trimmed X: 0.0, Y: 0.0, Z:-0.20107658

2020-08-28 12:12:27.981793+0530 TestThingy[706:49448] trimmed X: 0.0, Y: 0.0, Z:-0.20020154

2020-08-28 12:12:28.071640+0530 TestThingy[706:49448] trimmed X: 0.0, Y: 0.0, Z:-0.20079944

2020-08-28 12:12:28.161182+0530 TestThingy[706:49448] trimmed X: 0.0, Y: 0.0, Z:-0.20103921

RE: Thingy 52: Motion sensor (accelerometer) raw data in IOS is giving unit vector, I was expecting more of a m/s2 values. Is my assumption wrong?

Carl Richard — Thu, 27 Aug 2020 12:23:28 GMT

Thanks for clearing up.

Firstly. The documentation states that the raw data from the accelerometer is in Gs, just do make that clear. Hence, if you want m/s2 the raw data must be divided by 9.8.

However, the values you posted earlier does seem weird. Could you try to subtract 2 from every value and divide by 1G. It seems like the values are offset by 2G :)

Best regards,
Carl Richard

RE: Thingy 52: Motion sensor (accelerometer) raw data in IOS is giving unit vector, I was expecting more of a m/s2 values. Is my assumption wrong?

Prabhakar_katlakunta — Thu, 27 Aug 2020 09:02:30 GMT

Hi Carl,

Seems like I have some misunderstanding about the device outputs. Please help me in clarifying few queries of mine.

Expectation : I am trying to build a toy, which would measure the approximate force applied on this device from any direction.

So my problem is to measure the change in acceleration. But this device is giving me acceleration only in range (0.0 - 1.0) and no negative values, from accelerometer. I tried to scale the values but it will be of not much help because of the range which is always positive.

As you suggested I tried using gravity vector as well but below are my observations.

1. Gravity vector is giving all the values in range -9.8 to 9.8. But how I measure the force/acceleration on the Z axis, gravity axis, as it is going to always a constant.

2. Gravity vector will only help in identifying device orientation, but I need to identify the applied force to move this device.

Please help in clarifying my queries.

Thanks you in advance.

Regards,

K.Prabhakar

RE: Thingy 52: Motion sensor (accelerometer) raw data in IOS is giving unit vector, I was expecting more of a m/s2 values. Is my assumption wrong?

Carl Richard — Thu, 27 Aug 2020 07:46:10 GMT

Hello, again!

Then I misunderstood. My apologies. I spoke with one of the Thingy iOS app developers and he suggested that you should try to sample the values from the gravity vector instead as that is indeed given in m/s^2 from the accelerometer. It's this function from the Thingy app.

Hope this helps you.

Best regards,
Carl Richard

RE: Thingy 52: Motion sensor (accelerometer) raw data in IOS is giving unit vector, I was expecting more of a m/s2 values. Is my assumption wrong?

Prabhakar_katlakunta — Wed, 26 Aug 2020 15:07:23 GMT

Hi Carl,

Thanks for the quick response. I understood that three motion sensor data is been passed to the notification handler. I have handled in my code. Below is my code to handle it, if u notice I am trying to print only the first, ie accelerometer data itself.

peripheral.beginRawDataUpdates(withCompletoinHandler: { (success) -> (Void) in

NSLog("Raw data update")

}) { (accelerometerData, gyroscopeData, compassData) -> (Void) in

NSLog("Raw values \(accelerometerData)")

}

RE: Thingy 52: Motion sensor (accelerometer) raw data in IOS is giving unit vector, I was expecting more of a m/s2 values. Is my assumption wrong?

Carl Richard — Wed, 26 Aug 2020 11:46:55 GMT

Hi,

The raw data from the motion characteristic must sampled and converted correctly to obtain the m/s2 accelerometer data. The reason for this is that the measurements from all three motion sensors(accelerometer, gyroscope and compass) are sent as one. The link I previously posted points to how this is done in the app and I recommend following it as an example. Could you try that? Here is the link again.

Best regards,
Carl Richard

RE: Thingy 52: Motion sensor (accelerometer) raw data in IOS is giving unit vector, I was expecting more of a m/s2 values. Is my assumption wrong?

Prabhakar_katlakunta — Wed, 26 Aug 2020 10:58:53 GMT

peripheral.beginRawDataUpdates(withCompletoinHandler: { (success) -> (Void) in

NSLog("Raw data update")

}) { (arr1, arr2, arr3) -> (Void) in

NSLog("Raw values \(arr1)")

}

Using the above method when I am printing out the accelerometer values if It is giving me unit vector values. The sample output at console

2020-08-26 16:27:43.657397+0530 TestThingy[3278:594688] Raw values [1.999939, 1.9993896, 0.030792236]

2020-08-26 16:27:43.773514+0530 TestThingy[3278:594688] Raw values [1.9995422, 1.9995422, 0.030883789]

2020-08-26 16:27:43.863515+0530 TestThingy[3278:594688] Raw values [1.9999084, 1.9994812, 0.029724121]

2020-08-26 16:27:43.953406+0530 TestThingy[3278:594688] Raw values [1.9997864, 1.9995117, 0.031066895]

2020-08-26 16:27:44.073561+0530 TestThingy[3278:594688] Raw values [3.0517578e-05, 1.9992981, 0.030792236]

2020-08-26 16:27:44.163526+0530 TestThingy[3278:594688] Raw values [1.9998474, 1.9996643, 0.031036377]

2020-08-26 16:27:44.255128+0530 TestThingy[3278:594688] Raw values [1.9997559, 1.9992981, 0.030822754]

2020-08-26 16:27:44.373524+0530 TestThingy[3278:594688] Raw values [1.9996643, 1.9992981, 0.030670166]

2020-08-26 16:27:44.463550+0530 TestThingy[3278:594688] Raw values [1.9997253, 1.9994202, 0.03112793]

2020-08-26 16:27:44.553452+0530 TestThingy[3278:594688] Raw values [1.9997864, 1.9995117, 0.03125]

2020-08-26 16:27:44.673466+0530 TestThingy[3278:594688] Raw values [1.9998474, 1.9996338, 0.031280518]

2020-08-26 16:27:44.763441+0530 TestThingy[3278:594688] Raw values [1.9997253, 1.9994507, 0.030883789]

2020-08-26 16:27:44.853481+0530 TestThingy[3278:594688] Raw values [1.9997253, 1.999939, 0.028198242]

2020-08-26 16:27:44.973456+0530 TestThingy[3278:594688] Raw values [1.9999695, 1.9994507, 0.031097412]

2020-08-26 16:27:45.063600+0530 TestThingy[3278:594688] Raw values [1.9997253, 1.9996033, 0.030975342]

2020-08-26 16:27:45.153845+0530 TestThingy[3278:594688] Raw values [1.9996338, 1.9993896, 0.030883789]

2020-08-26 16:27:45.273472+0530 TestThingy[3278:594688] Raw values [1.9998169, 1.9997864, 0.030883789]

2020-08-26 16:27:45.363565+0530 TestThingy[3278:594688] Raw values [1.9999695, 1.9994812, 0.031188965]

2020-08-26 16:27:45.483496+0530 TestThingy[3278:594688] Raw values [1.9998779, 1.9995728, 0.031433105]

2020-08-26 16:27:45.573569+0530 TestThingy[3278:594688] Raw values [1.9996643, 1.9993591, 0.031951904]

2020-08-26 16:27:45.664374+0530 TestThingy[3278:594688] Raw values [9.1552734e-05, 1.9993286, 0.0317688]

2020-08-26 16:27:45.753466+0530 TestThingy[3278:594688] Raw values [0.0, 1.9996338, 0.030700684]

2020-08-26 16:27:45.873450+0530 TestThingy[3278:594688] Raw values [0.00024414062, 1.9993286, 0.030639648]

2020-08-26 16:27:45.963469+0530 TestThingy[3278:594688] Raw values [1.9994812, 1.9995117, 0.030914307]

2020-08-26 16:27:46.083952+0530 TestThingy[3278:594688] Raw values [1.9997253, 1.9992981, 0.030975342]

2020-08-26 16:27:46.173524+0530 TestThingy[3278:594688] Raw values [1.9998169, 1.9991455, 0.03112793]

RE: Thingy 52: Motion sensor (accelerometer) raw data in IOS is giving unit vector, I was expecting more of a m/s2 values. Is my assumption wrong?

Carl Richard — Wed, 26 Aug 2020 07:01:53 GMT

Hello!

How are you reading out the value? In the Thingy IOs app raw data is converted into m/s2 in this section of code.

Best regards,
Carl Richard