The current Flat Illumination System is customized to the 203mm(8″) Ritchey Chretien Telescope. A series of small LED projectors are installed in front of the optical tube assembly. When ready to take flats, the telescope is parked to face a white panel installed on one of the wall in the observatory. The projectors are turned on by Sequence Generator Pro via an Arduino micro-controller running a firmware (i.e. Arduino sketch) that emulates the behaviour of the Alnitak flat frame devices.
With the acquisition of the new wide-field telescope, the current system cannot be installed on the smaller 80mm telescope. A new flat fielding solution that can take flats for both the 80mm and the 203mm telescopes is required.
The new flat fielding system is inspired by “Cheap DIY Remote Controlled Flat Panel”
from Blackwater Skies
Parts
- Old Radio Shack 3-12V AC adapter (set to 9v)
- LM2596 DC to DC Buck Converter (9v–>5v)
- Micro-Controller (Arduino Uno)
- WayinTop DC 5V-36V 15A 400W Mosfet Dual High-Power Driver Module
- HSK B4/A3s Light Pad Light Box Ultra Thin 6 Millimeter with 8 Watt Led Light (Size: B4)
- 3D printed Arduino Uno Enclosure
- 1 USB Cable
- 15 feet of 2 wires cable (22 gauge)
Diagram
Theory of operation
- During flats acquisition sequence
- Arduino receives command via USB from Computer running Sequence Generator Pro and Alnitak driver
- The firmware (i.e. Arduino Sketch) translate the command from the PC and activate digital pin #2 with the proper pulse-width-modulation (i.e. duty-cycle: value from 0 to 255)
- the PWM signal drives the Mosfet module to switch on and off a the specified duty-cycle
- The Mosfet provide the modulated current to the LEDs in the light pad which turns on at the specified brightness.
3D Printed Enclosure
A model from Thingiverse
Wiring & Assembly
Firmware
The firmware (i.e. LEDLightBoxAlnitak.ino) was downloaded and then “uploaded” to the Arduino. The only modification made was the use of digital pin 3 instead of pin 13.
Software
Sequence generator Pro using the Alnitak driver
Light Pad – Light Box Preparation
The Light Pad had to be disassembled to in order to access the control circuit inside it. The operation was somewhat delicate because all the components are glued with double-sided tape. The 5V power cable was soldered directly to both led strips in order to bypass the control circuit. This way, the signal from the MOSFET was able to drive the LEDs across the 0 to 255 levels of intensity available through software. Without the bypass, only levels from 83 through 255 were available.
Wall Mounting
3D printed brackets were used to secure the panel to the observatory wall.
Testing
At intensity level 2 of the the Squence Generator Pro flat panel control, the Flats Calibration Wizard determined a 0.6 second exposure was enough to reach 32500 ADU (i.e. about 50% of full well capacity).
Results
A flat, rotated 90 degrees, was used to calibrate another flat resulted in a pretty evenly illuminated image. Results
