brainwagon

Maker Dino Segovis has a website called hackaweek.com where he tries to do a hack a week, streaming his construction via uStream, and then posting youtube video and details on his blog. This week, he decided to build a copy of Alexander Graham Bell’s PhotoPhone in celebration of the 131st anniversary of its unveiling to the public.

I must admit though: I am not quite certain how it achieves modulation. Here’s my boggle: the solar cell produces a changing voltage in response to changes in the total number of photons which hit the cell. In Dino’s video, the solar cell is much smaller than the sun’s reflection (the reflection is five or six diameters). If the amplitude of the movement of the reflected disk is just a diameter or two (as it appears to be in the video) the solar cell would appear to be constantly illuminated, and there should be no change in the voltage produced.

But it obviously works, so there must be something else going on.

If there was a variation the brightness of the overall pattern from center to edge, then its movement would cause an amplitude variation. But what is the source of this variation? Defects in the mirror? Mirror curvature? Changes in the brightness of the sun disk from center to edge? Those variations all seem to be pretty small.

I’ve seen music transferred by the bouncing of a laser beam onto a solar cell, and that confused me as well.

Something to think about (and maybe build) once I get my laser diode modules from Deal Extreme.