Accelerometer reading varying continously

Hello Akshay,

I believe the Tiva Microcontrollers Forum would be the best place to have this question answered.

In the meantime, can you please give more information regarding the application and setup? Under what circumstances is the reading varying? This information will help the apps engineer to find a solution.

Thanks and Best Regards,

Wen-Shin Wang

I am just interfacing accelerometer present in sensorhub .

 I am keeping sensor stationary on table.When am i reading accelerometer raw data keeping on table and reading data in infinite loop it is varying continously even though stationary.There is not much temperature difference encountered.

What could be the reason for this varying raw data of accelerometer??

Perhaps the accelerometer - its interconnect/power - are not to blame.  Or not - is the accel. being properly powered?  (might the "lash-up" of "MCU + expander boards" be placing too much demand upon 3V3 Regulator?)  Are connections checked - and solid?  Having a common ground - Sensor and MCU - very much "prime suspect..."  

To be fair - you do not describe/define "varying" - last 3 bits of any MCU's 12 bit ADC may not be rock-stable!  "Variation" you report does require further detail...

Use of a reasonable DVM may also serve to confirm analog variation - provided the variance is slow enough - and of sufficient magnitude - to be recognizable.

Suggest that you employ a pot - or 2 resistor voltage divider - and inject a mid-ADC-scale voltage into a (free) ADC channel.  This will confirm that your set-up/config of ADC - and follow-on ADC code is operating correctly.  When this is achieved - temporarily remove sensor input signals - replacing w/suggested pot/divider source - and note results.  (unlikely that pot or divider will yield "varying" raw data.)  

And - simply moving the Accel signals to another ADC channel may provide further insight.  (will "escape" individual channel/set-up issue)

Thanks,

Even my magnetometer in sensorhub is not working.I have set it up to work in Bypass mode.

So what initialization i have to do to read magnetometer data from mpu9150? 

Feel your pain - understand your frustration. 

Earlier post offered suggestions - have yet to receive comment.  

Shifting topics now - minus any of the earlier, specific tech information (requested in your behalf) - seems ineffective.  (both to your helpers and any/all follow-on readers - seeking to benefit from this thread...)

You said you're using an MPU9150?  Assuming you're using the SensorHub booster pack then the TivaWare examples should show you how to configure the device to get all 9D of sensor output.  The 9150 acts as an I2C master to the integrated magnetometer.  When you read the 9150 you should get ~18 bytes worth of sensor data (16 bits * 3 axes * 3 sensors).  Assuming, again, that you're using our sample code.  This, however, should be hidden from you by the MPU9150 Get*Float() calls.

As for your constantly changing values, as CB1 pointed out, you haven't quantified your fluctuation.  Did you enable any filtering on the 9150?  What sensitivity are you running?  12 bits of sensitivity on 1G (9.81 m/s^2) gives you 0.0024 m/s^2 resolution (9.81 / 4096).  In my experience at 2G sensitivity, the noise floor is around 0.2 m/s^2 or 0.02G's. 

--Miles

Stellaris Miles said:

You said you're using an MPU9150?  Assuming you're using the SensorHub booster pack then the TivaWare examples should show you how to configure the device to get all 9D of sensor output.  The 9150 acts as an I2C master to the integrated magnetometer.  When you read the 9150 you should get ~18 bytes worth of sensor data (16 bits * 3 axes * 3 sensors).  Assuming, again, that you're using our sample code.  This, however, should be hidden from you by the MPU9150 Get*Float() calls.

As for your constantly changing values, as CB1 pointed out, you haven't quantified your fluctuation.  Did you enable any filtering on the 9150?  What sensitivity are you running?  12 bits of sensitivity on 1G (9.81 m/s^2) gives you 0.0024 m/s^2 resolution (9.81 / 4096).  In my experience at 2G sensitivity, the noise floor is around 0.2 m/s^2 or 0.02G's. 

--Miles

Hi Stellaris Miles , could you take a look to this App for sensorhub? I am  getting inconsistent data in yaw.

http://e2e.ti.com/support/microcontrollers/tiva_arm/f/908/t/285768.aspx

Thank you