Negative value for accelerometer

SteelHeart

*Sorry if i post at the wrong section, i can't delete this post so I reused it to not double post.*

Hi i'm working with the MXD2125 acc and I trying to program it to drive the motor's PWM.
Anyway, take a look at my codes. I found this code as a base and editted it to suit my goal.

CON     ''General Constants for Propeller Setup
  _CLKMODE = XTAL1 + PLL16X
  _XINFREQ = 5_000_000

  xin = 17
  yin = 16
  period = 16665                ' number of microseconds for 60Hz frequency of pulses
  apin = 13                     ' output pin for motor a - left motor
  bpin = 14                     ' output pin for motor b - right motor

  memsic_mid = 400_000          ' middle of memsic range 
  memsic_range = 300           ' range reading divided by 100 to produce percentage
  angle_set = 0
  maxmemsic = 255               ' maximum possible reading from memsic
  
OBJ     ''Setup Object references that make this demo work
    pst         : "Parallax Serial Terminal"  
    MM2125      : "memsic2125"   
    PWM         : "PWM_32_v2" 


PUB Main_Program | dir_a,dir_b,i,forward, forward1,forward2, backward, backward1, backward2

   pst.Start(115200)      '' Initialize serial communication to the PC

   MM2125.Start(17, 16)               '' Initialize Mx2125
      
   PWM.Start                   '' Initialize PWM cog 

    
    repeat
      ''set up robot direction and speed using memsic X value
      
''    get x and y readings from memsic
    
      forward := MM2125.Mx         ''get memsic x reading
      backward := MM2125.Mx  
       
''    subtract mid range value from memsic readings      
      forward1:= forward - memsic_mid             ''subtract mid range from reading to get a value from -100,000 to +100,000
      backward1:= backward - memsic_mid

''    Convert memsic readings to a number between 0 > 100
      forward2 := forward1 / memsic_range           ''now have a value from -100 to +100                         
      backward2 := backward1 / memsic_range
                              
     
         pst.Str(String (pst#CE, pst#HM, "Forward Axis= "))
         pst.dec(forward2)
         pst.Str(String (pst#CE, pst#NL, "Backward Axis= "))
         pst.dec(backward2)

As you can see, I am now focusing on the X axis of the acc. I'll put Y axis at a later stage.
What i am trying to achieve is to set the backward axis to a negative value.

Example: 
At level, both forward and backward axis shows zero. When pitch up, forward axis increase, say 25 degrees. So backward axis will show and set to a negative value ( -25 degrees.)

The reason for wanting that is because I can set the if..else command to control the motor.

If forward > 0, forward motor speed slows down. Backward motor speed increase. until it balances. vice versa

Any kind of codes would be greatly appreciated.

P.S Can somebody try the code above to see if the scaling is right? Mines reading 28+- degrees when placed on the table.

Post Edited (SteelHeart) : 5/31/2010 4:55:08 PM GMT

Mike Green

When you defined MM2125, you used the name of the demo program rather than the name of the I/O driver object. There is no "start" method in the demo program.

hover1

Steelheart,

Goto the Sticky on the top of the Propeller Forums named "Propeller Education Kit Labs, Tools, and Applications"

There is a section on using Full Duplex with the Parallax Serial Terminal.

Jim

wjsteele

I think you just want to use "backward := -MM2125.Mx" instead of "backward := MM2125.Mx." (Note the minus sign in front of the Mx value.)

Then you'll have to set backward1 to "backward1:= backward + memsic_mid"

Bill