Matt Mets made this “Light Record:”

I am using some photocells to read the intensity of light that shines through a sheet of paper, upon which I have encoded an image using shades of grey. By spinning this paper around and shining a light through it, the image can be viewed on an oscilloscope. The circuit consists of two resistor dividers, one for each channel, made up of a photocell and a fixed resistor. When there is a large amount of light on the photocell, its resistance drops dramatically and the output voltage rises; when there is little light on the photocell, its resistance goes down and the voltage goes down as well. That’s it!

It’s the first of Matt’s ambitious Thing-a-Day efforts. – Link.

Becky Stern

Becky Stern

Becky Stern ( is a DIY guru and director of wearable electronics at Adafruit. She publishes a new project video every week and hosts a live show on YouTube. Formerly Becky was Senior Video Producer for MAKE. Becky lives in Brooklyn, NY and belongs to art groups Free Art & Technology (“release early, often, and with rap music”) and Madagascar Institute (“fear is never boring”).

  • Im

    Check that thingaday link

  • DonH

    How clever! You might experiment with making the data disks with a laser printer on a piece of acetate, or maybe just paper dampened with mineral oil. This device doesn’t seem to focus well, a fact which would allow bars to be used in an FM-like scheme. The CdS sensors are slow and tend to self-excite. Another way to make this would be with an op amp trans-resistance amplifier. This circuit can be speeded-up by using current-source loads rather than resistors.

  • japroach

    That music really creeped me out.

  • Becky Stern

    I fixed the link, thanks Im!