Reversed Scanner Project
About
The objective for this project was to create a device that could print graphical elements into a surface that had the ability to erase itself.
To do this, I explored the potential of a photochomatic ink. This special kind of ink, also found in sun glasses, has the ability to change color when exposed to UV light. In my case, it is blue when UV light is present, and while when it is not. The speed at which the effect dissipates depends on the color. Mine is blue and it fades away in about 2 or 3 seconds.
In order to print on this surface, a scanner was used because of its sliding arm. It allowed me to replace the regular light with a strip of 32 UV LEDs. These in conjucton with the sliding arm allow the scanner to print a 32×40 pixel image in an area of about 16 square inches. This is very low resolution but it is perfect for a prof of concept.
What i used to built it
| 1 | Scanner, with a working stepper motor |
| 1 | Arduino Duemilanove or Uno with a prototyping sheild |
| 2 | TLC5950 |
| 1 | SN754410 |
| 1 | 7805 Voltage Regulator |
| 1 | Power Supply, 12V capable of more than 1A |
| 32 | UV LEDs |
| 2 | 100nF Capacitors (ceramic) |
| 2 | Electrolytic capacitors bigger than 100uF |
| 2 | 1k resistors |
| 2 | 10k resistors |
The circuit
The surface
The UV reactive surfaces were created by spreading the UV reactive power on adherent film. This film is stiky on one side and not on the other. This allowed me to cover the adheret side of two films and them glue them together so that the adherent part faces the middle. This traps all of the power inside.
This ink can be found here: http://www.solarcolordust.com/
How it works
A processing program was created so that images could be captured using the computer’s webcam. Doing it this way avoids the extra work of creating a system for the arduino to capture the image, process it and save it.
All the image process is done by the computer. It captures the image, converts it to a 32×40 pixel image, then converts every pixel to black and white and only then sends them to the arduino using serial.
The arduino receives these values and interprets them as white, gray and black. These correspond to the three levels of the UV LEDs: no power, half power, full power. The reason why this was made this way was because the UV paper fades away too fast. If the whole scale was used it would disappear before we could perceive it.
To test if the concept was working I created two cards with high contrast images drawn on them. One with a smile =) and another with a uppercase F.
It is very hard to capture this with a camera but if the camera is set for long exposures, you get something like this image.
Demo of it working
Vision
This technology could be improved to create a new kind of paper. If the ink lasted a day and the printing resolution was much much higher, people could print their newspapers using this kind of technology, reusing always the same sheet.
It is true that devices like the kindle already are able to produce similar results with their E-Ink display. However, this alternative opens the possibility to have something just like paper–very thin and very light–that can be used over and over.
