Elgin Observatory
HOME

Automatic Dome Rotation

Adding computer controlled dome rotation allows me to sleep while doing all night time series imaging.

Pierre de Ponthiere from Belgium has designed a dome rotation system,
"LesveDome", based on a Velleman K8055 interface board. This board is
a USB interface providing input and output circuits for computerized control: Velleman K8055.
Pierre provides a complete set of plans and control software on his observatory web page.
His presentation shows an installation in an Exploradome.

My dome is DIY homemade, so my dome drive is also DIY homemade.
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!!

HOME