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.