Add support for controlling LED-based enlargers

[dkonigsberg]

This is something that isn't likely to be provided on the first "shipped" version of the Printalyzer, as it would require extensive changes to the way enlarger control is handled.

The basic idea is to be able to control enlargers that need something a bit more sophisticated than simply switching a mains power outlet on and off. The problem is that there is no real standard here, and every different build of an LED-based enlarger would likely need something slightly different. Its also hard to draw the line between what should work "out of the box" and what should require some customized electronics on the part of the user.

There are two main approaches that could be made to work for this:

• Have a port on the back with a series of GPIO outputs with PWM capabilities, hopefully robust against misuse, that can interface to any random hardware someone wants to build an adapter for. Doing it this way may unfortunately require the Printalyzer firmware to be customized to the peculiarities of what is being interfaced to.
• Have a more generic "enlarger control interface" port on the back, which uses a flexible I2C-style interface similar to the meter probe on the front. This could be done in addition to the existing relay-mains-control outlets, or instead of them. Then, a series of modules could be developed to connect to this port, with their own dedicated MCU and capable of speaking a common protocol. These modules could be made in enlarger-type-specific variants, or even individually programmed based on what the user wants to do.

[dkonigsberg]

The latest hardware/firmware now has a DMX512 control port, which is designed to be used for this purpose.