Gear Tooth Counter for height

[jhersh]

Originally Posted by DonRotolo

What you may want to use is called an "Interrupt". This is a special hardware connection (to the Digital sidecar) that signals the cRio's processor "STOP Whatever you are doing and run this piece of code. Immediately. Now". In your case, that code might add +1 (or subtract -1 if the lift motor is running backwards) to a counter that keeps track of lift position. Clearly, the code must be as brief as possible, since your processor is literally unable to do ANYthing else while the interrupt is active. (The interrupt gets activated by the sensor signal)

For an application like this, an interrupt is unnecessary... the FPGA design has counter logic in it that will deal with counting up or down as you wish. It is much faster and has no impact on your robot code's execution speed. Use interrupts only as a last resort.

-Joe

[Tom Line]

Sean - the danger in using a gear tooth counter in this manner is that it is a 'relative' measurement system.

That means that where ever your lift happens to be when you power it on is the zero point. If the lift is set 3 inches high, then you may run the lift too high at the end of the motion. Or, worse, if you have a power fluctuation on the field, the lift will lose it's 'zero' position.

You are better off if you use something that is absolute. To that end, there are absolute encoders and multi-turn potentiometers that you could use. In 2008 we used a 10 turn pot from radio shack that worked very well. In 2010, we did as you are suggesting and used the encoder to measure how far we unwound our winch. It was a constant hassle to make sure the winch always started in the same position.