I have some questions about using rfid tags in an arduino project. I have a 60' cable on a reel and I would like to know how much cable is out at any given time. I was thinking about heat shrinking an rfid chip at one foot intervals and having a rfid reader at the reel to read chips and display cable length on a lcd. The cable is ~5mm in diameter. I have researched and found an rfid chip that will work, the small glass tags, but they are too expensive for this project, ~$3 each.
I am wondering if anyone knows of a cheaper, better style of tag that would work for this application. I am also open to a different approach to measuring the cable length.
Paul- I have not made the reel yet but all wound up I would imagine that 60' would be roughly a 6" long x 4" diameter cylinder. I would like it to be accurate to within a few inches. I think the length of cable let out with one turn of the reel would differ whether it was a full spool or towards the end of the spool. I could see counting turns if the cable was wound only one layer deep across the whole reel.
Mike- That is a great idea! I am going to look into it. That may be what I end up doing.
The difference between the diameter of the spool and the diameter of the outer layer of cable is going to be a function of the spool diameter. Wind the cable around a large spool and the depth of cable on the spool will be small, meaning that unwinding an outer layer will not spool off that much more cable than unwinding the bottom layer.
Besides, you can have multiple slots and one light source/detector, so you can measure small movements of the spool.