Equipment: System control and image acquisition

System control and image acquisition

Up till the end of 2020 I worked with the outdated DOS-computers that were state-of-the-art when I set out for astrophotography with CCD's some 20+ years ago. The analog-to-digital converter was build on a board that only fitted an ISA-slot and the main image acquisition program, written in Borland Pascal, operated only under DOS. For continuity of my hobby, a new 'platform' was required and the Raspberry-Pi (RPi) was my choice.

Since the Linux kernel of the RPi (at least the one I'm using) is not realtime, while my camera-electronics, once triggered, outputs the analog signal of the pixels in a continuous, uninterruptable flow, a FiFo-buffer was needed. An ATMega 1284p microcontroller with 16kbyte SRAM acts as buffer between the 12-bit ADC and the RPi. The interface with the CCD-camera remained functionally unchanged and a Serial-In Parallel-Out (SiPo) buffer was used to limit the number of GPIO lines required for controlling the camera. This SiPo is also used for controlling the shutter and filterwheel (via an additional micro-controller). The mount-controller and focusing unit are controlled via an i2c-connection.
Here is an overview of all connected components and especially of the 'Control Unit' containing, amongst others, the Raspberry Pi (3B).

Qt Creator IDE, the free version for open source users, was selected for developing the main program in C++. An annotated screen shot is shown here. The program, amongst others, enables to:

Select the connected CCD-camera and select the mode (full-frame/frame transfer, binning, Left- or Right CCD-output)
Select the filterwheel and the filter
Perform an automated acquisition of images with different filters. Store them on the connected USB-stick.
Perform a focus scan, determine focus quality and suggest the optimum focus position of the focusser
Control the mount controller and its 4Q-guider
Show information regarding signal levels, RA-position, star-tracking accuracy and system status

The following screen shots show the start-up menu, the help menu (mainly in Dutch), a menu to start automated acquisition and the resulting output:


Start-up menu	Help menu showing functions	Continuous acquisition start menu	Output during continuous acquisition	An annotated screen shot

I combined the 'Control Unit' with an LCD-screen, key-board, mouse, and all cables one-sided attached, in one easily portable unit replacing the DOS-computer(s), separate power supplies and a myriad of cables.
It also saves a lot of lugging with hardware and cables!

For the interested, the electronics of the 'Control Unit' is given here:

Overview of the System controller and connected CCD, filterwheel, focuser and mount-controller
The ADC and microcontroller FiFo, and the Real-Time_Clock (RTC) and their connection to the GPIO of the RPI
The interface to the CCD-cameras using a Serial-in Parallel-out buffer
The controller that handles the filterwheel and shutter
All power supplies needed for the CCD-camera, thermo-electric cooler, RPi and Mount controller. Also the 2-stage Peltier current source is shown in this schematic