Scalable information display

Posted on July 5, 2015

I started thinking about how to display persistent but dynamic information on my wall at home. Persistent meaning I could see it every time I walked past, and dynamic meaning I could change it at any time. I’m imagining a large display perhaps something like this size:

SLFD concept 1

An LCD/LED screen would obviously be horrendously expensive. A projector would also be expensive, and would require its own mount away from the wall. I wanted it to be as inexpensive as possible. In fact, as area-scalable as possible. In other words, if the area is increased then the cost must increase by the smallest amount possible.

I came up with a solution, and I’ll get to that. But first — this could have a variety of really neat uses, for instance:

  • 2D timeseries: Plotting a daily-updating graph of some quantity over time — such as bank account balance, BMI, stock price, etc.
    • Yes there are smartphone apps for this, but it requires some effort to pull out your phone, log in and see it — there is something fundamentally different about having this information in front of your eyes every day where you can’t avoid seeing it. If you are trying to lose weight or build your bank account, for instance, this is much more motivational.
  • Family whiteboard: We have a whiteboard at home where we keep to-do’s, shopping list, calendar, etc. But if I think of something to add while I’m away from home, I have often forgotten to add it by the time I get home. With this invention you could dynamically add text remotely to a shared display.
    • Yes there are smartphone apps for shopping lists etc too — but there is something special and different about having a large whiteboard at home to share this information. If there weren’t, no home would have one.
  • Signage: Certain signage needs to not change often or quickly, but needs to be inexpensive. Imagine large wall-display menus in restaurants, or session information at conferences.
    • Yes you can just print a large-format menu or poster each time, but this can get expensive over time.
  • A real wall: I can write on someone’s facebook wall. How cool would it be to write on their actual wall in their home?
    • …without them getting mad, that is.

The problem:

  • The display must be cheap.
  • The display must be area-scalable as discussed before.
  • The power consumption must be small.
  • The thickness must be small.
  • The display must be computer-controlled.
  • The information displayed is not required to change very often or quickly.

A solution:

The solution is essentially a scrolling dry-erase board. Or chalkboard or other erasable board. (But way cooler — keep reading…)

If I hide the frame on the concept drawing I presented above, you can see that the front is actually half of a continuous scroll, and on the back there are two blocks, representing the writer and eraser. The writer can move in one dimension and the scroll can move in one dimension – thus pens attached to the writer can write at any arbitrary point on the scroll. (Similar to a plotter or vinyl cutter.) There may be a variety of colors of pen. The eraser may just erase everything that brushes past it (perhaps able to engage or disengage with the scroll), or it may be motorized too and possibly combined with the writer.


I had a vinyl cutter at home that wasn’t being used, so I decided to make a simple (but small!) prototype to explore the idea.

I’ll put this on instructables along with the computer control code in the next month or two, but here’s a summary. I hacked together a wooden frame with two kitchen rolling pins. The plotter (a Silhouette Portrait, the white spaceship-thing) moves the scroll and also moves the writer. In other words, no change to the plotter, other than that I put a whiteboard marker in it. The scroll (not shown in the first image) wraps around two kitchen rolling pins. Along the rear of its travel, the scroll brushes past whiteboard erasers (only one shown in the first image — the fully-assembled one has enough to cover the entire scroll width).



Here’s a video showing the thing in action, and the computer control via an inkscape extension called in a batch script from the command line. As described in the section below, I’m working on a way to take arbitrary text or html5 canvas input from a computer or web server, and have it print on-command.

Future improvements

  • Making it cooler:
    • I have basic scripted control of the plotter. Next I’d like to be able to take arbitrary text or drawing (html5 canvas) input from a computer or web server, and have it print on-command. For example, it may print tweets or facebook posts. It may find the value in my bank account (or weight, or stock price, etc) and plot a single point each day, building up a 2D graph over time.
    • There are a variety of other features I want to add. For instance, if I manually write on the whiteboard then a pressure sensor could detect that something has been added, and the drums roll around while a 1D scanner (harvested from a flatbed scanner) scans the whiteboard to find what the user has just manually written. For a home whiteboard this bridges the gap between the old-fashioned folks who want to write manually, and the new-fashioned folks who want to also be able to add content or view content remotely. Another example is automatically-retracting nibs to stop the whiteboard markers from drying out when not in use.
  • “Hey but it’ll look like … a whiteboard [or chalkboard]. Not like a menu I want to put in my restaurant [or wherever].”
    • Maybe but not really. It doesn’t need to be white, for starters. Here is an example of a black dry-erase with neon markers. In fact that looks a lot like this fancy restaurant menu. That restaurant menu is something that could easily be drawn on this plotter and changed daily. Some algorithms could be added to make the font more like handwriting (so for instance not every “e” is drawn the same way, as with a computer font). Here are some more examples of painstaking fancy handwritten signs that could be drawn with this.
    • There is no reason this cannot include 20 different color pens, other than the marginal cost of adding a pen-lowering mechanism for each color. The result can be quite colorful. And whereas a whiteboard consists of mostly white with a few chicken-scratches of ink on, if desired, the drawn figures can be colored in and cover large areas, leaving a minority of background visible.