LightWriter Clock – reborn

The initial LightWriter Clock was designed to play with the notion of the ephemeral nature of time. The current time is “written” with light onto a phosphor-coated panel, such that the image of the time slowly fades away before the new time is written.

“Such are the metaphors we live with, Grasshopper!”

The original unit was designed and built almost a year ago yet has sat gathering dust for all that time (no pun intended). Now, with a new paint job (yes, really!) it is ready to be reborn.

LightWriter Clock

LightWriter Clock

Watch this space…
Video of the LightWriter Clock in action coming soon

To recap, the LightWriter Clock is built using two carriages that move independently on a common steel rod. Each carriage is connected to an arm that meet together to form an equilateral triangle, the apex of which contains a high-power LED. Articulation of the carriages – each controlled by a NEMA-17 stepper motor – allows the LED head to move from side-to-side and forward-to-backwards. The LED is mounted upright on a heat-slug and sits underneath a phosphor-coated plastic panel. The LED traces the four numbers of the time on the underside of the panel so that the phosphor allows the image of the numbers to persist. The images slowly fade away and the new time redrawn.

LightWriter Clock

Carriage details

LightWriterClock-p03

LED head showing

LightWriterClock-p02

Under the hood

LightWriterClock-p01

Carriage and limit switch details

The stepper motor control software has been rewritten along with the arrays for each of the number positions (hours and minutes) of the clock. The “space” traversed by the head was mapped into an “effective area” using the units of stepper motor steps. Arrays of points were then created for each of the numbers that could be drawn in each of the four digit position (10s hours, 1s hours, 10s minutes, 1s minutes) within this drawing area.

LightWriter Clock

LightWriter Clock: Effective Writing Area

In addition, the stepper motor homing algorithms were rewritten to include the new micro-switch limit switches. The clock writes out the four digits of the time every 5 minutes.

Light problems abound…

While all of the electronics and mechanics work as expected, I am having problems getting the phosphor-coated panel to glow properly in other than pitch darkness – I rather think I’ve added too much and the trace of light in the phosphorescent paint is too spread out. Reviews of the “glow-in-the-dark” spray paints sold in the big box stores suggest that I shouldn’t waste my money and the results using several rather expensive eBay purchases of thick phosphor paints have been rather disappointing. I’ve recently ordered some 3W LEDs with wavelengths around 350-400nm to see whether UV light excites the coating better than the high power blue LED I’m currently using.

I shall keep experimenting so stay tuned for more….

Come on... leave a comment...