Fade

Fade transforms any surface into a “glow in the dark” screen. You firstly coat the wall with a special transparent spray paint. After dark install your laser projector nearby. The laser draws with light and leaves an eye-catching fading trail behind.

History
The vision for Fade is to catch people’s attention by transforming an regular wall into a fading out screen. The bypasser doesn’t know where the message is projected from because of the speed of writing. Moreover, the message he’s reading is quickly disappearing, as if it was being erased or censored. The expected reaction is then to increase the focus on the message and play with the effect to associate the idea with the disappearing effect.

The system needs a prepared wall to work. However the spray paint containing the phosphorescent pigment is almost colourless and only appears greenish when many layers are applied. This makes the preparation much easier than using regular spray paint. It can be discretely applied, and the paint is relatively resistant to weather wear which means an event can be planned quite in advance or layers can be applied on several occasions.

Instructions
Main article: Fade Instructions Here is the bill of materials you need to make Fade.

First you need to laser cut the structure out of a 3mm thick material such as acrylic, plywood or MDF. You can download the file here. Laser cutting is cheap and easily available in Fablabs. Check out here where there is one near you. Once you have your parts, you can follow these instructions for the assembly. The next step is to solder the board.

Hardware
The phosphorescence is activated by a 405nm laser source. The laser diode is sourced from a £5 laser pointer (<5mW output power). The laser beam is then reflected on two mirrors mounted perpendicular to each other and fixed two the axes of two stepper motors. The idea is that a rotation on the first motor will move the projected dot along the X axis while the second motor will control the Y axis. The laser source and the motors are oriented so that the beam has the largest possible range. Two endstops are placed on the course of two 3d printed flags to find a reference position.

Software
The resolution for this concept is defined by the angular minimum rotation the system can perform. The stepper motors used here are only 200 steps per full rotation or 1.8 degree angle resolution. This is way too big to project anything complex such as text at long distance (approx. 30 cm at 10m). This is solved by the use of stepper motor driver such as Pololu A4988 with the ability to do microstepping. The driver then creates intermediate stable positions which results in a multiplication of the steps available by a factor of 16 in the case of Fade. The number of steps available is now 3200 per full rotation, which equals to an angular resolution of 0.11 degree or 1.9cm at 10m.

Contact
You want to replicate this tool with the help of a streettoolbox contributor? You can contact us to talk about it at [mailto:info.streettoolbox@gmail.com info.streettoolbox@gmail.com]

More info
Montana Night Glow spray paint can