The paper

Lightroom is based on using cyanotype-covered paper that is sensitive to light and changes its color after it is exposed to sunlight for about 15 minutes. We opted to making our own cyanotype paper that fits the needed dimensions to produce the results we were looking for. Using a mix of Potassium Ferricyanide and Ferric Ammonium Citrate, we created a liquid solution that we could apply to any surface and have full control of. This has allowed us to easily test different kinds of paper, exposure times, exposure strengths, and effectiveness.

Ideally we would use a watercolor-like paper that is texturized and is made to be able to withstand a substantial amount of liquid. This ability is important because the paper needs to be able to not break apart or become wavy when dyed with several layers of the cyanotype solution. It becomes quite crucial when taking into consideration the fact that the exposed paper has to be thoroughly washed in order to "develop". Unfortunately, a nicely-textured watercolor-like paper does not bend and roll nicely and requires quite a lot of torque power to turn when rolled.  

After testing various kinds of papers (courtesy of ITP Design Lab) we found one that was able to do both: hold onto multiple layers of dye, and be light and flexible enough for rolling using our solar-powered DC motor. That said, the visual quality of that paper is significantly reduced due to it being very light and more on the glossy side.

The mechanism

One part of the mechanism controls a shutter-like behavior that is made up of two layers of paper with matching hole matrixes. A servo motor is used to push one of the layers back and forth, letting light go through when the two layers are aligned.

The second part of the mechanism is in charge of the film-roll-like behavior, and consists of a right-angle DC motor, dowels and the paper.

We 3D printed a mount, a cogwheel, and a rail to convert the servo motor's rotational energy into a linear one. We also printed pillow block bearings and a mount for the DC motor. Dental rubber bands were put on the wood dowels to increase the friction with the paper and help it roll with ease.

The electronics

The shutter mechanism is driven by an Arduino nano 33 IoT. The Arduino is connected to a WiFi network, and runs a program that sleeps and wakes up in regular intervals (~10 minutes). Every time it wakes up, the program fetches the time, and if it is daytime, it drives the servo to either open or close the shutter.
Every sleep and wakeup cycle, the program also sends a signal that we are able to monitor on our computers in order to make sure it's still operational (Thank you networking team!)

The rolling mechanism is driven by a custom made analog circuit that is trying to act like a small battery — charging when it's sunny and discharging when it's not. After many many attempts and iterations we weren't able to make this work exactly as we imagined, but ended up making a circuit based on the "Miller" solar engine with a few minor adjustments like adding a voltage detector instead of using a diode. This configuration makes it so the motor is activated with short spurs of energy under less-than-sunny conditions.

The Arduino is powered by an IoT battery pack that is connected to a small solar panel. The analog circuit is powered by an additional small solar panel and is driven directly from it.

Because it was meant to live outside for a few weeks, the project needed to be enclosed in a container that is weather-proof. It also needed to be light-proof aside from our controlled shutter.  

We designed and fabricated a box that houses the mechanisms, the paper, and the circuitry. The box has to be both resistant to weather conditions such as wind and rain, but it also has to be easy and convenient to handle. Every few days we must physically go to where the project is located so we can replace the already-exposed roll of paper with a new one.

The IoT battery pack and the Arduino are contained inside of a specially-made enclosure that is watertight.

From the moment we installed it on site, up until April 27th — the project was running continuously and was sending us a signal every ~10 minutes. Then, on April 27th we received a signal on 12:07AM, then another one ten minutes later, and then, we suspect, the battery ran out. The next signal was on 2:21PM the following day. The Arduino seemed to be working again for about 40 minutes, and then stopped communicating again. It has been coming and going ever since. We suspect that the battery is pretty much depleted and that the sun hours in the last few days weren't enough to fully charge it.

Unfortunately it appeared like there was an issue with the rolling mechanism where the paper would get stuck and not fully roll. As this is an analog system we couldn't really monitor it from afar and only realized this was the case when we came to retrieve the first print.