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Code for the Arduino and Raspberry Pi now up on GitHub - very much work in progress

Overview;

The printer consists of the following parts; Data processing & overall control, a pair of stepper motors to control paper feed (rigid base board carrier) and print head translation and finally the print head itself. In order to attain the desired image resolution, the print head spinning mirror will scan a width of roughly 5mm, to generate a strip similar to that from an inkjet printer. The strips are then built up to form the completed image.

This is the current layout for the various modules (continued below the break).

Figure - System overview (click to expand for more detail)

Background;

The Iron based photographic printing (Siderotype) process dates back to the Herschel Cyanotype, better known as blueprint; which uses the sensitivity to UV light of specific Iron compounds to produce a print. There are numerous other 'alternative' photographic processes many of which should also be suitable.

With the advent of digital cameras it is necessary to print negatives onto transparency film, to allow contact printing, similarly when making enlargements, smaller negatives are scanned and then printed to transparency film.

However printer ink is designed for visible wavelengths and its response to UV wavelengths is variable enough between batches to require repeated time consuming calibration. The transparency film and inks are also fairly costly. The aim for this project is to remove them from the equation, and thus simplify the process from finalising an image to being able to process it. At the same time, allowing full scope in choice of chemistry and media.

I've had questions regarding using this method with other printing chemistry methods such as tintypes. Any chemistry that is sensitive to UV and does not have a very short life-span (wet plates may be possible with humidity control) should be viable. The more sensitive the chemistry, the faster the process should print, up to the limits of the electronics; laser power/signalling speed trade off.

Details;

The following design units have so far been identified. Each needs designing, prototyping and integrating;

All of the setup and ~static systems are controlled by the Arduino using a low speed serial connection to instigate the setup and calibration steps and provide feedback to the piZero for logging/calibration/etc. Whilst the piZero can concentrate on feeding the data to the FIFO buffer and moving the print head and paper feed system.

The UV laser is highest power available (for reasonable cost); BDR-209 x16 bluray diode, nominal 600mW but they have been tested in short duration by others up to 1000mW. So this is as good at it gets with the current technology. A shorter wavelength would be better, but again they are only available at much lower powers (and significant cost). Note that any longer wavelength than 405nm is a no-go, such as the multi-Watt 450nm diodes, that will burn a hole, but wont produce an exposure.

Development Notes (for future, if budget allows; will get prototype running first):