In my childhood I discovered an interesting phenomenon: if I connected a light source to a sufficiently amplified television receiver, and waved the light around in front of a video camera, I could get the light to function as a 3D augmented reality display that would overlay the sightfield of the camera, as virtual information on top of physical reality. I grew up at a time when technology was transparent and easy to understand. Radios and televisions used transparent electronic lamps called "vacuum tubes" where you could see inside them and they revealed all their secrets. I then witnessed a transition into an era of opacity in which scientific principles were concealed inside integrated circuits with closed-source firmware. And while machines became more "secretive", we entered a new era in which they also began to watch us and sense our presence, yet reveal nothing about themselves (see a short essay I wrote about this metaphenomenon). I wanted to be able to sense sensors and see what they can see. So I invented something I called the PHENONAmplifier, a device that amplifies physical phenomenon in a feedback loop of revelation.
It worked by video feedback, and because of the feedback loop, it solved one of the most difficult problems in augmented reality: alignment between the real and virtual worlds. As a result I was able to make artistic "lightpaintings" or "light drawings/graphings" as scientific visualizations where the degree of visibility of each sampled point in space to a surveillance camera could itself be made visible. I called this "Metasensing", i.e. seeing what a camera can see (sensing sensors and sensing their capacity to sense). As a professor, I teach this to the students in my Wearable Computing and Augmented Reality class every year, but a number of people have attempted to reproduce this interesting scientific result and have had difficulty (it is somewhat difficult to get all the conditions right for the phenomenon to occur). Therefore I came up with a very simple way to teach and explain this phenomenon. Each student builds a very simple one-pixel camera, and a very simple 3D augmented reality system with a light bulb or LED to learn about this interesting effect. Once understood, this effect has many uses both artistically and scientifically. See for example IEEE Consumer Electronics, 4(4) Pages: 92 - 97, 2015.
Get the materials together and prepare them for assembly:
Prepare the components by cutting off the leads to an appropriate length, especially the parts that are in the feedback circuit, e.g. the 47 Mohm resistor and the capacitor, as well as the photodiode.
To identify the polarity of the photodiode, connect it to a voltmeter. The anode terminal is the one that will provide a positive voltage when light is incident upon it. As shown in the picture, you can see more than 0.3 volts under illumination of a typical desk lamp. Sometimes the polarity is indicated by the lengths of the leads, so you might want to mark the positive (anode) lead with a red sharpie, as indicated.