Dear all,
I have written some code in Java for Android as part of a larger framework
that can read streaming Shimmer data over Bluetooth.
To test it's accuracy we connected two Shimmer devices, one that streams
over Bluetooth and another that stores data on the Shimmer itself.
When we compared results there appears to be a slight shift in the values
(I only tested with accelerometer data). I would like to know if there is
an explanation for this besides sensor displacement.
Another question I had relates to the sampling rates of the sensors and the
transmission rate of the Bluetooth radio. When I sample the sensors at 250
Hz will I then also receive the packets at this frequency?
I read one byte at a time from the Bluetooth socket and when I have
received a full packet I decode it as follows:
public float[] decodeSensorData(byte[] data, int size) {
float[] values = new float[(mNumChannels+1)];
if (data[0] == PACKET_START) {
for (int j = 0, k = 0; j < mNumChannels; j++, k += 2) {
values[j] = getChannel(data[4+k], data[3+k]);
}
values[mNumChannels] = getChannel(data[2], data[1]);
return values;
} else {
Log.d("Shimmer", "Package error");
return null;
}
}
private float getChannel(byte high, byte low) {
float temp = 0;
temp = (short)(high << 8) | (low & 0xFF);
if (((short)temp & 0x8000) > 0) {
temp = (long)temp & 0xFFFF;
}
return temp;
}
I then send the data to native library for further processing.
I would like to thank you in advance,
Gabriele
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