Help with Position Sensing URGENT!

Hi all,

Okay so here is my project. I am using a continuous rotation servo to run a spool or pulley that raises and lowers a small object. I am operating these servos via dead man buttons (one for going up and one for going down), so the operator must actively be pushing the button in order for the motor to move. I need to install some sort of rotary encoder or optical encoder in order tell the absolute position, but know nothing about encoders (I know have the work but do not know how to code or spec them out). I need for the operator to know when that object has descended the full amount (20+ feet underground). My question is what type of encoder would go good for this application and how the heck do I go about integrating it into my existing code. I have all of the code and circuitry done for running the servos up and down via dead man switches. I've been doing a lot of research and can't seem to find what I want. Any help is greatly appreciated! Thanks specs:

Board: Arduino Mega Servo: Parallax continuous rotation servo Circuit: custom (making my own) Power: AC/DC conversion (8v system)

Just about any quadrature shaft encoder could be used - don't use a "knob encoder" as these have detents for feedback to humans, which would interfere with the spool rotation.

I would couple the encoder to the spool that lowers the object, and count rotations of the spool. See this introduction for coding: http://playground.arduino.cc/Main/RotaryEncoders Google will show you lots more.

Thanks for the reply! I will look into those, and that’s definitely an option I will consider. What if lateral space is limited? My system needs to have six of these motor/spool combinations stacked in a line (so one motor will be only a few cm away from the previous spool). I hope that makes sense, I can upload a diagram to illustrate that a bit better. Are there any sort of encoders that are electronic and can be mounted to the board or are do they all mechanically have to be driven by the object being rotated? Again Thanks for the info!

Depending on the accuracy needed and winding speed you might be able to use a simple light/dark sensor on the winding shaft. Or magnetic (hall) sensors.