The driver is a reversible 1/4" hand drill with a gear reducer.
The drive wheel is a chain drive sprocket from a dirt bike.
The dome "rack" is pre-punched hobby metal from a hardware supply store.
The original design calls for two photo sensors that are activated by a wheel with holes to interrupt
the light path from source to detector. The detectors are offset such that the two sensors complement
each other in "gray-code" sequence. This provides increased resolution over a single sensor.
I use a single micro-switch with a magnet that is drawn to the sprocket's teeth as they pass by.
This greatly simplies the pickup circuit since there is no power needed at the sensor
and only one switch is used. The dome "rack" has 431 holes in the circumference of the dome.
This provides more than adequate dome rotation resolution of 0.8 degree.
Pierre's software is very flexible and provides three options for sensing dome rotation:
"Gray Coder", using two complementing sensors; single sensor "Hole-NoHole" transition;
and single sensor "Hole to Hole" transition. The operations are as the names imply.
Hats off to Pierre de Ponthiere for a great contribution to amateur astronomy!!