DRO, deskjet encoder

I gave up on the parallel port interface to the 7266 - too lazy to
make up a seperate power supply for it. Ended up point to point wiring
the 7266 on an ancient proto board that fit in the isa bus once I
trimmed a few fingers of the connector - that way I can power
everything off the computer.

I basically built Tom Kulaga's circuit for two axis (one chip). Had
some problems transfering files from my net-connected linux box to the
unconnected box I put the board in (still runing dos/windows) so I
ended up writing my own program in basic using Tom's as a guide (that
7266 has the wierdest data sheet I've ever seen - but not bad to
program once one gets used to it).

The only thing I couldn't figure out is that in BCD mode the counters
seem to go up to 153 and then rollover. Binary mode has each byte go
to 255 as one would expect, but what is 153 good for? Am I missing
something obvious?

Hooked up the HP deskjet encoder to test it. Looks like 500 cpr or
2000 with quadrature. I think maybe I'll put it on the crossfeed
screw on the lathe for my "manual numerical control". Let's see, .125
lead/2000 gives .00006275" per count <yeah, like I can hold that>.
Perhaps with a software alarm every time the axis reverses direction,
to remind me to take out the backlash.

Headed out in search of tubing to mount the encoder strip for the Z
axis tomorrow...

Chris

--
Christopher C. Stratton, stratton@...
Engineer, Instrument Maker & Horn Player
(978)538-5179 work, (617)492-3358 home
30 Griswold Street Cambridge, MA 02138
http://www.mdc.net/~stratton