After a while, the living FPUs got bored with their task, so they helped me in creating an automated version using Lego mindstorms. See attached Pictures.
Originally Posted by clayne
While this was a "just for fun project" to entertain my kids, I was surprised how well it integrated with the software program and the splitgrade approach. I was not just using filters for hard and soft contrast, which got automatically selected during the final print exposure sequence. Even better was the red filter, which automatically got moved out of the way after the pre-countdown is done and the exposure starts. This helps positioning the hands for dodging before the start. I thought that the vibrations introduced by the motordrive for the filters to the enlarger column would be more of a problem than they really were. Anyhow, that was just a PoC and it was fun building it. I think if I was going to incorporate such functionality productively, Iíd rather use LEDs in green, blue/UV and red to get the same thing achieved.
What Iíve done in the meantime was making prints whenever time allowed. I have now just over 200 prints in the DB, using this system exclusively. It works really well for me. I made some improvements regarding the usability in the dark. Also Iíve added a USB footswitch I got from amazon for just 9 Euro. Wouldnít want to miss that convenience anymore. Also I hooked up a second light source (my backup enlarger set at a certain height and aperture) to the second relay on the interface card. This is controlled by a paper flashing and contact printing part of the application. Standard times for this mode are also stored in the paper database and are used depending on the paper type that is selected for the print that is worked on.
Regarding the analyser part, I went with a TSL235R sensor on an arduino, which in turn is hooked to the computer via USB. I went with the arduino approach, as this potentially could be used for a homebrewed LED head as well, because the arduino has PWM outputs I could use there.
The sensor basically gives me an irradiance reading in uW/cm^2. I use this to calculate a paper index for the highlights by making a test print. All I do at the moment is measuring the print highlight region on the easel and multiply it with the time it took to make a proper zone 7 tone of that region. This is my paper index for now. It works somewhat ok to get me in the ballpark for teststrips, which is all I wanted from this system. However as I save the paper index with all the other information in the print database (in the paper table), I think a lot of potential is wasted here. At least some contrast / filter calculation would be nice. Iím still trying to get my head around this and come up with a good approach, but probably am just too stupid to do it properly. Any hints in that direction would be greatly appreciated!