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MEMs ADXL001-70BEZ chip Need Help! — Parallax Forums

MEMs ADXL001-70BEZ chip Need Help!

TasnimTasnim Posts: 4
edited 2011-02-07 10:53 in Accessories
Hi,

I am using the ADXL001 chip to measure the acceleration of the actuator arm of a hard disk drive. I purchased the chip/IC only (not the evaluation kit). I built the circuit exactly similar to the application circuit (fig. 20) of the datasheet. Here's the link:
http://www.analog.com/static/imported-files/data_sheets/ADXL001.pdf

Now I gave a Vs = +5V and when I measure the output voltage, (using a simple multimeter) from Xout (pin 6) I only get 2.5 V. When vibrating/shaking the ADXL001 chip in the X-axis (or in the direction of Pin8 ) I don't get any changes in the output. What can I do to get a change in the voltage or any changes at all? How do I measure the output sensitivity of the ADXL001? Do I have to give a supply current of 2.5mA? What am I doing wrong, my objective is to see a significant change in the output when I shake/move the ADXL001 IC in X-axis.

My project is at a halt because of this ADXL001 chip. Please advice me on this as it is part of an important project.

Thanks
Tasnim Siddiqi

Comments

  • LeonLeon Posts: 7,620
    edited 2011-02-06 08:29
    Post the schematic.
  • Mike GreenMike Green Posts: 23,101
    edited 2011-02-06 14:03
    A multimeter averages its reading over time. The amount of time depends on the meter. You need to look at the output voltage using an oscilloscope or something similar with a rapid response.

    If you want to measure the sensitivity of the ADXL001, you will need a known acceleration at a known time and some kind of measurement device with a fairly rapid response. An appropriate analog to digital converter with a sample and hold input should do the job triggered somehow by the acceleration.

    Remember that this is a support forum for Parallax devices. We can offer you support for the use of Parallax-sold sensors with Parallax microcontrollers. We can give general advice on the use of other sensors with Parallax microcontrollers and we can give general advice on the use of Parallax-sold sensors with non-Parallax microcontrollers. We can give some very general advice on other sensors like the one you're using. I suggest you look on the manufacturer's or distributor's websites for further documentation or other support.
  • TasnimTasnim Posts: 4
    edited 2011-02-06 20:16
    Hi attached is the schematic. I built the circuit exactly like the schematic, gave a Vs = +5V and measured the output from a multimeter!
    ADXL001_Schematic_Application Circuit.JPG
    ADXL001_Schematic_Application Circuit.JPG
    640 x 512 - 20K
  • Mike GreenMike Green Posts: 23,101
    edited 2011-02-06 20:46
    Read the datasheet! What you are measuring is exactly what you should have at rest. As I said before, a multimeter averages its reading over a period of time. If you shake the accelerometer, the multimeter will probably continue to read the same as it does at rest because the acceleration averages out to zero.
  • TasnimTasnim Posts: 4
    edited 2011-02-07 10:14
    Hi Mike,

    I used an oscilloscope to view the signal. There is actually a lot of noise (+/- 50mV) and it is hard to distinguish the noise part from the actual signal. There seems to be an output (my gut feeling) but the problem is due to noise signal.

    Do you feel a notch filter will remove the noise frequency?
    Another problem is that the ADXL001 has an acceleration range of +/- 70g. Its sensitivity is 24 mV/g. Obviously just shaking a the chip will not subject the chip to more than 1.5g. THerefore I believe may be the chip is not sensitive enough given my noise level! ANy thoughts?
  • Mike GreenMike Green Posts: 23,101
    edited 2011-02-07 10:34
    You have to fix the noise problem first. There's a whole page in the documentation on noise, filtering, etc. Read it and follow the suggestions. I don't know how you've got the device mounted. You're dealing with small voltages. You have to be very careful about how you've mounted the device, how you've routed the conductors, what other signals are present nearby, etc. Once you've cleaned up the noise problem, maybe you need some amplification with wide dynamic range.

    What's the estimated acceleration of the disk drive actuator? That's what you want to measure in the end.

    Before you start "throwing around" ideas like notch filters, you should think about what they do and how one would affect what you're trying to measure.
  • LeonLeon Posts: 7,620
    edited 2011-02-07 10:53
    How has the circuit actually been constructed? That is probably the cause of the problems. It needs a properly designed PCB with the other components mounted close to the chip.
  • medayubpmedayubp Posts: 1
    Dear Tasnim,

    My name is Medayu and I am a senior year of Instrumentation major at Meteorological Climatological and Geophysical State College, Jakarta. In my introductory, I've conducted undergraduate research. Recently I happened to find this forum and it is related to my current project. I'm using a sensor: ADXL001 and I found it difficult to reach the Arduino sensor library/source code. If possible where I could reach you to have a discussion about ADXL001. I look forward to hearing from you because your response will be a great help to me. Thank you for your consideration.
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