(Updated 19 Aug 2008 - Alternative servo power source) 

Neon Controller Installed on LHIRES III

Control is from the PC via the USB cable. (It ended up running very close to the grating micrometer adjuster!)

The neon position is controlled by a servo coupled to the rear screw of the neon shaft.

The 12v power to the neon is separately controlled. This means the switched off neon can be moved into the beam to act as a shutter for taking darks.

No permanent modification to the LHIRES is needed except for replacing the  cross head screw on the rear of the neon axle with a hexagon socket head screw to give a more positive drive.

The box sits on the top plate of the LHIRES. It is slid into engagement with the neon axle and clamped to the side of the LHIRES with the wing nut. 


Neon Controller

The servo and circuitry was built into a small (MB2) project box
The Protech B305 servo gives plenty of torque to move the neon. The mounting screws are in slotted holes to allow adjustment to align the drive shaft to the neon axle.

The drive shaft is short length cut from a hexagonal allen key. The servo drive shaft was drilled out until the key was a push fit. It was then glued into position

Controller Circuitry

A "Motor Bee" control board is used to control the servo and neon 12v power. It is based on a PIC IC with a built in USB interface and can control the servo and 4 high power variable outputs, one of which is used to switch the neon supply. It also has several digital inputs and outputs so has capacity for future expansion.

The servo was originally powered from the USB 5V supply. (The red wire from the servo plug to the 5V side of a resistor on the board.)  This needed a powered USB hub to supply enough current.  The controller has now been modified to  include a 5V voltage regulator (7805) providing the power from the 12v neon supply instead. (Roll your mouse over the image to see the new layout)

Control Software

The system testing was done using the "VBmotor" sample visual basic program supplied with the Motor Bee board. The plan is to  write a dedicated program eventually, but it is a long time since I did any programming!

The servo calibration is done by positioning the neon shaft half way between the "in" and "out" positions and setting the servo to its neutral position (128) before engaging the servo drive shaft. (The neon shaft is rotated slightly until the hexagonal drive shaft engages).  The  servo settings are then found which rotates the neon until it is just off the "in" and "out" stops, so that the servo is not under continuous load in either position. (100 and 170 for my setup. Check that the neon position is correct using the guide camera image.)

The neon power is switched on and off with the output 1 set to 255 (maximum)