LED Matrix And A Phototransistor Make A Reverse Camera

A digital camera has an array of sensors that captures light reflected or transmitted onto it. This build is something closer to a reverse camera – a single sensor that makes images on a matrix of LEDs. And we think it’s pretty neat.

We have to admit to being a little confused by [marciot]’s LED matrix scanner when we first stumbled upon it. From the video below we thought that the LEDs in the matrix were being used both to detect incident light and as a display. We’ve seen LEDs used as photodiodes before, so such a contraption could work, but that’s not what’s going on here. A phototransistor is wired to an Arduino Uno and positioned above a 32×32 RGB LED matrix. A scanning routine rasters over the LEDs in the matrix while the sensor watches, and then the program turns on the LEDs that the sensor saw during the scan. Positioned far above the matrix, a large disc of light results, making it look like the phototransistor is beaming light down onto the matrix. The effect is reinforced by placing something between the sensor and the matrix, which casts a virtual shadow. Used close to the LEDs the sensor acts more like a light pen.

It’s a cool effect and it looks like a fun project to throw together. Refresh time could perhaps be a bit snappier, though; maybe an ESP32 could help with that.

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Text Projector With — You Know — Lasers

We missed [iliasam’s] laser text projector when it first appeared, perhaps because the original article was in Russian. However, he recently reposted in English and it really caught our eye. You can see a short video of it in operation, below.

The projector uses raster scanning where the beam goes over each spot in a grid pattern. The design uses one laser from a cheap laser pointer and a salvaged mirror module from an old laser printer. The laser pointer diode turned out to be a bit weak, so a DVD laser was eventually put into service. A DVD motor also provides the vertical scan which is just a slight wobble of a mirror. A Blue Pill CPU provides all the smarts. You can find the code on GitHub.

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Lighting Up The Night Sky With A Flying POV Display

We’ve seen loads of persistence of vision displays before, but this sky-writing POV display seems as though it may be a first. And we have to agree with its creators that it’s pretty cool.

The idea man on this was [Ivan Miranda], who conceived of a flying POV as a twist on his robotic dot-matrix beach printer. But without any experience in RC flight, he turned to fellow YouTuber [Tom Stanton], whose recent aerial builds include this air-powered plane, for a collaboration. [Ivan]’s original concept was a long strip of Neopixels that would be attached to the underside of a wide-wingspread plane. WIthout much regard for the payload limits of most RC planes, he came up with a working display that was 3 meters long. His video below shows it in use in his shop, with some pretty impressive long exposure images.

[Tom]’s part was to make the POV display flyable. He cut the length down to 2 meters and trimmed the weight enough to mount it to a quadcopter. Ungainly as the machine was, he was able to master its control enough to start painting pictures across the twilight sky. The images at the end of his video are actually stunning – we’re especially fond of Thunderbird 2, which takes us back to our childhood.

We’re not sure what the practical uses of this are, but that’s hardly the point. It’s enough that it’s an interesting project from an unlikely duo. Continue reading “Lighting Up The Night Sky With A Flying POV Display”

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.

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Smart Phone Camera Turns Laser Cutter into Hi-Res Scanner

Getting decent macro photos always seems to be a chore. Some important detail always seems to be just outside of the depth of field, or you have to be zoomed in so close that you get great detail in one spot but miss the big picture. [Nate B] had such a problem while trying to document some PC boards, and he came up with a nifty hack that uses a laser cutter and a smart phone camera to do the job.

Pv150a-front
Click for detail.

Having first tried scanning the boards with a flat-bed scanner but finding the depth of field unsatisfactory, [Nate B] then went on to his Samsung phone’s camera. Set to panorama mode, he manually scanned across the boards and let the camera stitch the images together. The results were better, but the wobblies got the better of him and the images showed it. He then decided to use a laser cutter — with the laser disabled, of course — as an impromptu X-Y stage to raster his camera above the boards. In a slightly cringe-worthy move, he gingerly clamped the phone to the cutter gantry, started the panorama, and let the cutter move over the board. This results in a rock-solid pictures of his boards with a lot of detail – perfect for his documentation. As a bonus, the honeycomb laser cutter bed makes for an interesting background texture.

Obviously anything could be used to raster a camera and achieve similar results, but full points here for maximizing available resources and not over-complicating a simple job. Yet another reason you can use to justify that laser-cutter purchase.

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Oscilloscope doubles as a serial terminal

PC-based USB oscilloscopes are fast becoming all the rage. [Matt Sarnoff’s] Terminalscope takes the reverse approach, adapting an oscilloscope into a full serial terminal. You may have seen something similar before in the Dutchtronix/SparkFun O-Clock, but [Matt’s] project goes one further by adding a PS/2 keyboard port for full bidirectional serial communication, and with much sharper display resolution to boot.

The mostly VT-100 compatible Terminalscope is built around two AVR microcontrollers: an ATmega328P runs full-tilt to generate the video signal and handle serial I/O, while an ATtiny45 handles keyboard input to avoid interrupting the ’328’s duties. Rather than vector trace each character, a raster-scanning approach is used: the beam follows a fixed X/Y path (like a television), while modulating the Z input (beam intensity) to form an image. The device can be connected to a PC via serial port or USB-to-TTY adapter, or directly to another microcontroller to debug serial output.

We recently showed an oscilloscope being used as a multichannel digital logic display. The Terminalscope provides yet another use for this essential bench tool and could nicely round out a “poor man’s” testing setup. The schematic and full source code are available for download.