Accelerometer help

Comments

• kf4ixm Posts: 529

  2010-03-04 22:20 edited 2010-03-04 22:20

  How do you have it wired up? what does your code look like? i would really need to see a schematic of how you have it connected and attatch your code to your post to be of any help.
• Sunflower Posts: 48

  2010-03-04 23:04 edited 2010-03-04 23:04

  The wires are simple MEMS Xout to Zin pin, 5V and GND. Battery power supply on MMC carrier board with capacitors. No vibration and stable room temperatures. Output is +/- 2 brads when level. Is that the expected performance of the MEMS?
  
  
  Zin PIN 11 ' Tilt Z Accelerometer MEMSIC 2125
  
  work4 = 0
  FOR work.HIGHBYTE = 1 TO 64
  PULSIN Zin, HiPulse, zRaw
  zRaw = (zRaw */ Scale) '$0C0=Scale pulse to uSeconds 0.75 BS2p
  zRaw = zRaw/10
  work4 = work4 + zRaw
  NEXT
  zRaw = ((work4 / 64) - 500) 'Binary SIN -127 to 127
  DEBUG SDEC zraw," "
  NEXT
• hover1 Posts: 1,929

  2010-03-05 00:32 edited 2010-03-05 00:32

  An Accelerometer outputs in terms of g's, not degrees.
  
  Jim
  

  Sunflower said...
  I bought a Memsic 2125 from Parallax and can not resolve accuracy better than +/- several degrees. Is this normal or am I doing something wrong?
• kf4ixm Posts: 529

  2010-03-05 00:43 edited 2010-03-05 00:43

  i think you're using code for the compass module instead of the accelerometer code found here...
  
  http://www.parallax.com/Portals/0/Downloads/src/prod/3rd/Memsic2125Demo.zip
• Sunflower Posts: 48

  2010-03-05 01:17 edited 2010-03-05 01:17

  I left out the "8" factors for g force as I only need the SIN(angle) for relative tilt. From Memsic2125Demo.zip below. MEMS resolution is discussed in detail in small parts of a degree tilt, but are the actual measurements only good to a couple of degrees on each axis?
  
  
  GOSUB Read_G_Force ' read X and Y
  
  brads = (xmG / 8) ATN (ymG / 8) ' calculate angle
  degrees = brads */ 360 ' convert to degrees
  
  Read_G_Force:
  PULSIN Xin, HiPulse, pulse ' read pulse output
  pulse = pulse */ Scale ' convert to uSecs
  xmG = ((pulse / 10) - 500) * 8 ' calc 1/1000 g
  RETURN
• hover1 Posts: 1,929

  2010-03-05 01:48 edited 2010-03-05 01:48

  @Sunflower
  
  I stand corrected. I have not followed the Basic Stamp software for this unit. I'm more familiar with the interface on the Propeller Chip.
  
  The demo software does indeed report back degrees of tilt.
  
  I will have to load up my BOE and try this out.
  
  Jim
• Sunflower Posts: 48

  2010-03-05 02:01 edited 2010-03-05 02:01

  Using ATN from two pins (X&Y) does smooth out the data to +/- 1 degree. I am running out of pins and would like the Z axis from one additional MEMS to one Stamp pin to measure dish tilt +/- 45 degrees, well within MEMS capability. But the Binary SIN rapidly fluctuates +/- 5 (a couple degrees) on just one axis. I guess I can accept that and still love the MEMS.