Joe, thanks for all the ideas. I chose to go with the coil and magnet. I did this for several reasons, mainly I didn't want to wait for a new hall effect module to come in.
I used the coil from a 24v relay I had, I left the bar in the center of course. I got a small but quite strong round magnet from the earpiece of an old cell phone. I connected the coil to a NPN transistor which I forward biased to increase the sensitivity and then ran the output of that NPN into a PNP to give a good positive pulse to the 16F628A.
As a test while everything was still breadboarded, I put a cardboard disc about 6" in dia. on a variable speed drill, taped the magnet to the edge of the disc a gave it a spin. The readout appears to work perfectly, varying with the speed of the drill very reliably ! And the magnet will still work when it's about 1" away. I will have it setup so that the coil and magnet are in close proximity though.
Now I'm going to do the board design in Eagle, then use PCBGcode and mill several boards out on my CNC mill and I should be set.
I'm real happy about this and again, I really appreciate the code and all the help !
Best regards,
Sam
EDIT: I forgot to mention that it displays only in multiples of 60. ie: 60,120,180,240, etc. RPM. Not "linear", I left the formula as displays=(displays*60) as that's all I need for the way I'll have it attached to the first machine I use it on.
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