Memsic 2125 code?

[ScaleRobotics]

Looking at your result for xRaw pulse (in your level.doc), and running through the formula, it looks to be correct using the original formula given:

    PULSIN PORTB.1, HiPulse, xRaw
    xRaw = xRaw * 2
    ' g = ((t1 / 0.01) - 0.5) / 12.5% ' formula from data sheet
    xGForce = ((xRaw / 10) - 500) * 8 ' Modified for our PIC - Converts to 1/1000 g's

xRaw = 2472
xRaw * 2 = 4944
xRaw /10 = 494
494 - 500 = -6
-6 * 8 = -48 (-.048 g's which can probably be calibrated for.)

57.5*(-48/10) =274 hundredths degrees, or -2.74 degrees.

seems like its pretty close given the original equation. Since your total period is short, that might explain why its off a little bit. T2 was supposed to be 10ms (and is assumed as such in the code.)
I would try calibrating it using a -494 , instead of a -500 and see what you get.

Edit: I see now you are calibrating with the *20 and /99.

This method workes pretty good to 45 degrees or so. At 90 degrees, it obviously doesn't work very well, and is about 24 degrees off.

[Ramius]

Hi Walter,
You are correct and just a minor "brain cramp" with the * vs /. With the logic analyzer results (Pulse Width.doc) the results showed a T1 of 502 which is why I used this number. The sensor document, 28017, says the "duty cycle" can be from 48.7% to 51.3% so the logic analyzer reading of 50.2% made sense. In the formula they use 50%. It is also assumed that the pulse timing is 10 ms which would be true if if the PWM signal were 100 hz. Again the logic analyzer show a frequency of 101 hz so the overall timing becomes 9.9 ms. Okay, both are minor corrections. You can not do a divide by 9.9 as it is not a whole number so to change the *2 to *20 allows the divide by 99 (9.9). Where I am having trouble with the formula is that if you point the sensor front edge down by 30-40 degrees then xRaw reading becomes about 414 which results in a number in the 65,000 range as 414 - 494 will give a result of -80. My best guess is that one would have to a lower number such as the 414 rather than 494 for the range of the sensor pointed down? Thanks, Ed