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Dome Control

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Another 486 (PC2) runs a qbasic programme I have written to control the bits that scope.exe doesn't. It does this by using a couple of parallel ports linked to interface boxes I have made. The first one contains 2 darlington arrays of 8 drivers. These ULN2003A chips are brilliant for connecting PC to motors and relays as pull up resistors and fly-back diodes are built in so no other components are needed. This box connects to the focus motor and the filter motor so focus and filter selection can be made in the warm room while looking at the out put from the ccd camera.
Also connected to this box is the two ac relays which control direction and power to the dome motor. Feed back on dome and scope position is from a modified mouse. Basically the optical components of the mouse 2 axis are split. One rides on the dome base ring the other underneath the scope. In put into dome.exe is by a standard mouse driver. Two extra switches wired to the mouse buttons provide an over ride to move the dome while at the telescope.

Temp change over a summers afternoon and night with fans and secondary heater working.

The second interface contains an 8 channel a to d converter and another darlington array. The a-d converter records the voltage from 4 temperature sensors on the scope. ( Air temp,primary mirror, secondary and the iron tubes at hold it all together). I hope to characterise the scope in terms of focal length changes with temperature and include automatic temperature compensation into the focusing. At the moment the PC just keeps dew from the secondary using a ring of resistors powered from the darlington array.

If you fancy having a play with the software it is here dome.bas



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Copyright 2006 Steve Chambers. All Rights

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