Sarah Hirschman
M.Arch. 2011

For the final project, I was excited to combine some of the knowledge from the molding/casting weeks with that from the composites week. I wanted to use the charlieplexing technique to drive a series of LEDs embedded in candlestick-looking-objects, as switched on and off by presence of plates or other objects on the tablecloth that connects them all.


I milled one half of the candlestick shape on the Shopbot and made a negative mold from it in Smooth-On OOMOO 25.


Then I created strings of LEDs to insert into the candlesticks, connected in series. From the datasheets, and using an online LED calculator, I found that I needed to attach a 10 Ohm resistor to each set of two LEDs.


I then got to work on the "tablecloth" portion of the project. This consisted of two pieces of fabric sandwiching a layer of neoprene.


I cut small holes in the neoprene, following a method that Hannah from High-Low Tech had shown me when we were doing a workshop together in Taiwan last year. The holes allow contact through the neoprene between two pieces of conductive fabric, which sets up a touch-sensitive switch in the circuit. I attached the power wire from the battery through this conductive fabric switch so that only when the area is depressed and the two pieces of fabric in contact did the lights go off.


Testing that the fabric was as conductive as I had hoped - success!


The LED strings were then worked into shape for the candlestick, connected to the switch and tested. Success again!


Preparing to fuse the two sides of the candlestick... I secured the LED string inside one half of the resin/hemp composite candlestick so that I could make sure they'd stay in place while I was winding more red-dyed string around the two halves.


But no dice!

Even though the LED string and circuit worked when I was preparing the pieces to go together, once the resin connectors were attached and hardened, the LEDs stopped working!

I opened up some of the edges to get a better look at the parts and to test if even single LEDs would work.


I opened up the bottom thinking that perhaps I had accidentally created a short somewhere.

Unfortunately, this didn't work as a debugging process, and I can't get any of the LEDs to light up. Potential reasons include the resin's conductivity and the possibility that when fusing the two halves of the candlestick together, i accidentally compressed the LED string to such a point that the power and ground cables touch somewhere.


This is how it would have worked in this prototype - I like how the candlestick looks, and I believe that this method could still be viable if I gave some more time and attention to the effects that the wet Smooth-On resin has on the LEDs. I just assumed that it would have no effect, but that's improbable.

I'm exicted by the potential of this project to create a kind of interactive tableware with a simple set of tools - now that I have the candlestick mold, I am sure I will continue to test different ways that it can be used.




h a simple set of tools - now that I have the candlestick mold, I am sure I will continue to test differe