Hi,
I am using Thingy 52 to measure the acceleration from accelerometer. I was expecting values like m/s2 but I am seeing values in unit vector, ie, values between (0 - 1.0), I can't see negative values as well. How do I get actual values, ie, > 1? Please hep if my understanding is wrong.
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]
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
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
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
Hi Carl,
Solving this problem is important to me. Request you to help.
Thanks & Regards,
K.Prabhakar
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
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
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
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
