Old Chart Recorder Becomes Single-Pixel Scanner

With so many ways to capture images from paper, do we really need another one? Especially one that takes 15 minutes to capture a 128×128 pixel image? Probably not, but building a single-pixel RGB scanner is pretty instructive, and good clean fun to boot.

We have to admit that when [Kerry Wong] scored an ancient Hewlett-Packard X-Y chart recorder a while back, we wondered if it would lead to anything useful. One may quibble with the claim that the Lorenz attractor plotter he built with it is useful, and this single pixel scanner is equally suspect, but we like the idea. Using an Arduino to drive the X- and X-axis of the recorder through a raster pattern over the bed and replacing the pen with an RGB sensor board, [Kerry] was able to collect the color data for each pixel and reconstruct the image. It wouldn’t be too hard to replicate this if you don’t have an analog X-Y recorder, which just goes to show that not everything needs to be steppers and digital to get something useful done. Or at least semi-useful.

As for the RGB sensor used, they’ve made appearances here many times before, mostly in M&M sorters but with the occasional synesthesia simulator.

7 thoughts on “Old Chart Recorder Becomes Single-Pixel Scanner

  1. I made something like this a very long time ago, but it was black and white and did not record digitally. It just moved back and forth, then down a row to get through a page. It dropped a pen on seeing black, and raised it on white. Basically it worked the same way a key copying machine does, but it made crude photocopies instead of keys. Ah to be 12 again…

  2. I remember this hack from ZX Spectrum – there were several plotters available for it, so it was only a matter of replacing the pen with a gutted one containing a photodiode or phototransistor and a bit of electronics. No fancy color sensors required.

    Here is the article from the Czech journal VTM from 1989:

    It is in Czech, but there are some example images (1 bit, black & white), the pen and the electronics used. It was to be used with Alfi – a simple plotter kit built out of Mercur (a very popular Czech construction set similar to Meccano):

  3. Or the color errors could be due to failure to correct the gamma or rebalance the white point of the output…

    It’s vaguely a shame to not take advantage of the 16-bit ADC inside the sensor, and just linearly scale the results into an 8-bit range.

  4. I got WAY better resolution doing exactly the same thing back in 1982. Only difference was I used a digital plotter (HP7225A) and had to scan three times to resolve color. Sensor was a cad sulfide cell out of an instant camera. Measured output using a Datron system DMM. Everything controlled over HPIB with an HP9836. Still own several HP controllers and plotters.

  5. There was a way to use a needle printer as scanner by putting a LED and a phototransistor with some lightpipe onto the printer head. Input was fed into the datasette port of the C64. Amazing for this time :-D

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