Analog math

Hi All,
I'm having a mental block when it comes to some analog math:

Using a DL-06 PLC from AutomationDirect with a 12-bit analog combo input/output card (0-4095).

I have a joystick connected to the input that reads ~2045 when centered, ~220 when full left, and ~3960 when full right. I need to scale the signal so that when the joystick is moved off center, I get a 0-4095 output on my analog output, no matter the direction of the joystick. 0-4095 output either full left or full right.


(full left) 220 ------ 2045 ----- 3960 (full right)
joystick
center


(full left) 4095 ------- 0 ----- 4095 (full right)
analog
output

I will handle joystick direction (and thus, motor direction) with comparative contacts.

I've done plenty of scaling when going from 0-4095 to engineering units, but this midpoint application has me stumped.

EDIT:
I've found this app note from AD, and I think it may help with the joystick-to-the-left math, but I'm still stuck:

http://www.automationdirect.com/static/manuals/t1krsssm/appxb.pdf


Thanks,

-rpoet

You just need a preliminary step where you calculate the difference from center position. I would just subtract 2045 from whatever the current reading is and take the absolute value.

Roughly you should end up with a number between 0 and 1800. Then you can scale the 0-1800 to output to 4095 the way you normally would.

ndzied1 said:

You just need a preliminary step where you calculate the difference from center position. I would just subtract 2045 from whatever the current reading is and take the absolute value.

Roughly you should end up with a number between 0 and 1800. Then you can scale the 0-1800 to output to 4095 the way you normally would.

Click to expand...

While I understand the concept of subtracting a constant and taking the absolute value, I'm having trouble getting this into code. The DL-06 doesn't seem to deal with negative numbers very elegantly, or at least I don't know how to make it.

The joystick-to-the-right part was easy, since it's all positive numbers. I've got that part worked out no problem.

See the attached screenshot for what I've got so far. I've slightly adjusted the center value to K2110, as that's where it's settled after some use of the joystick.


Thanks,

-rpoet

Add another rung with the test of the value being less than the center point. In your math blocks just swap the first two - LD CenterPoint, SUB InputValue. Keep the others the same.

bernie_carlton said:

Add another rung with the test of the value being less than the center point. In your math blocks just swap the first two - LD CenterPoint, SUB InputValue. Keep the others the same.

Click to expand...

Thank you, Bernie. I knew it was that simple... it was just eluding me. It's been a long week, and it's only Tuesday.

Bernie, you've helped me out on several DirectLogic math-related questions over the years. If you're ever in the NYC area, beers are on me. Thank you.


-rpoet

You are welcome and beers are always appreciated. But it may be a while before I get there.