# Op-Amp Challenge: Interactive Analog LED Wave Array

A while back, [Chris Lu] was studying how analog circuits, specifically op-amps can be used to perform mathematical operations and wondered if they could be persuaded to solve differential equations, such as the wave equation. After sitting on the idea for a few years, it was time to make it a reality, and the result is an entry into the Op-Amp Challenge.

Unlike many similar interactive LED matrix displays that are digital in nature (because it’s a lot easier), this design is pure analog, using many, many op-amps. A custom PCB houses a 4×4 array of compute units, each with a blue and white LED indicating the sign and magnitude of the local signal.

The local input signal is provided by an IR photodiode, AC coupled to only respond to change, with every other circuit sharing a sensor to keep it simple. Each circuit is connected to its immediate neighbors on the PCB, and off the PCB via board-to-board connectors. This simple scheme makes this easily scalable if desired in the future.

[Chris] does a great job of breaking down the math involved, which makes this project a neat illustration of how op-amp circuits can implement complex mathematical problems in an easy-to-understand process. Even more op-amps are pressed into service for generating the split-rail voltage reference and for amplifying the weak photodiode signals, but the computation circuit is the star of the show.

We like analog computing a fair bit around these parts. Here’s a little something we were previously drooling over.

# NASA Lunar Probe Finds Out It’s Not Easy Being Green

If you’re a space fan, these are very exciting days. There’s so much happening overhead that sometimes it can be difficult to keep up with the latest news. Artemis I just got back from the Moon, the International Space Station crew are dealing with a busted Soyuz, SpaceX is making incredible progress with their Starship architecture, CubeSats are being flung all over the solar system, and it seems like every month a new company is unveiling their own commercially-developed launch vehicle.

So with everything going on, we wouldn’t be surprised if you haven’t heard about NASA’s Lunar Flashlight mission. The briefcase-sized spacecraft was launched aboard a special “rideshare” flight of SpaceX’s Falcon 9 rocket back on December 11th — tagging along with two other craft heading to our nearest celestial neighbor, the Japanese Hakuto-R lander, and a small rover developed by the United Arab Emirates. There was a time when a launch like that would have been big news, but being that it was only the second of seven launches that SpaceX performed in December alone, it didn’t make many headlines.

But recently, that’s started to change. There’s a growing buzz around Lunar Flashlight, though unfortunately, not for the reasons we’d usually hope. It seems the diminutive explorer has run into some trouble with its cutting-edge “green” propellant system, and unless the issue can be resolved soon, the promising mission could come to an end before it even had a chance to start.

# Walk-Bot Is A Navigation Device For The Vision-Impaired

For the vision impaired, there are a wide variety of tools and techniques used to navigate around in the real world. Walk-bot is a device that aims to help with this task, using ultrasound to provide a greater sense of obstacles in one’s surroundings.

Created by [Nilay Roy Choudhury], the device is intended to be worn on the waist, and features two sets of ultrasonic sensors. One set is aimed straight ahead, while the other points upwards at an angle of 45 degrees. An infrared sensor then points downward at an angle of 45 degrees, aimed at the ground.

The distance readings from these sensors are then collated by a microcontroller, which uses trigonometry to determine the user’s actual distance to the object. When objects are closer than a given threshold, the device provides feedback to the user via a buzzer and a vibration motor. The combination of three sensors looking out at different angles helps capture a variety of obstacles, whether they be at head, chest, or knee height.

It’s unlikely that a complex electronic device would serve as a direct replacement for solutions like the tried-and-tested cane. However, that’s not to say there isn’t value in such tools, particularly when properly tested and designed to suit user’s needs.

We’ve seen some great projects regarding visual impairment before, like this rig that allows users to fly in a simulator. If you’ve been working on your own accessibility tools, don’t hesitate to drop us a line!

# IR Remote Tester Helps You Crack The Code

Even though some devices now use WiFi and Bluetooth, so much of our home entertainment equipment still relies on its own proprietary infrared remote control. By and large (when you can find them) they work fine, but what happens when they stop working?  First port of call is to change the batteries, of course, but once you’ve tried that what do you do next? [Hulk] has your back with this simple but effective IR Remote Tester / Decoder.

By using a cheap integrated IR receiver/decoder device (the venerable TSOP4838), most of the hard work is done for you! For a quick visual check that your remote is sending codes, it can easily drive a visible LED with just a resistor for a current-limit, and a capacitor to make the flickering easier to see.

For an encore, [Hulk] shows how to connect this up to an Arduino and how to use the “IRremote” library to see the actual data being transmitted when the buttons are pressed.

It’s not much of a leap to imagine what else you might be able to do with this information once you’ve received it – controlling your own projects, cloning the IR remote codes, automating remote control sequences etc..

It’s a great way to make the invisible visible and add some helpful debug information into the mix.

We recently covered a more complex IR cloner, and if you need  to put together a truly universal remote control, then this project may be just what you need.

# Your Own Home IR Cloner

Many devices use infrared (IR) as a signalling medium like, for example, RGB LED strip controllers
modules and some TV controllers. Often times these signals aren’t meant for secure applications which means the functionality can be reproduced by simply replaying back the received signal verbatim. Sometimes, enterprising hackers want to reverse engineer the IR signals, perhaps to automate some tasks or just to get a better understanding of the electronics we use in our everyday life. To help in this effort, [dilshan] creates an open source hardware IR cloner device, capable of snooping IR signals and retransmitting them.

The IR cloner is a sweet little IR tool that can be used to investigate all sorts of IR signals.
In addition to the source code and design files, [dilshan] has also taken care to create detailed documentation as an addendum to the video on assembly and usage. Continue reading “Your Own Home IR Cloner”

# PixMob Wristband Protocol Reverse-Engineering Groundwork

The idea behind the PixMob wristband is simple — at a concert, organizers hand these out to the concertgoers, and during the show, infrared projectors are used to transmit commands so they all light up in sync. Sometimes, attendees would be allowed to take these bracelets home after the event, and a few hackers have taken a shot at reusing them.

The protocol is proprietary, however, and we haven’t yet seen anyone reuse these wristbands without tearing them apart or reflashing the microcontroller. [Dani Weidman] tells us, how with [Zach Resmer], they have laid the groundwork for reverse-engineering the protocol of these wristbands.

Our pair of hackers started by obtaining a number of recordings from a helpful stranger online, and went onto replaying these IR recordings to their wristbands. Most of them caused no reaction – presumably, being configuration packets, but three of them caused the wristbands to flash in different colors. They translated these recordings into binary packets, and Dani went through different possible combinations, tweaking bits here and there, transmitting the packets and seeing which ones got accepted as valid. In the end, they had about 100 valid packets, and even figured out some protocol peculiarities like color animation bytes and motion sensitivity mode enable packets.

The GitHub repository provides some decent documentation and even a video, example code you can run on an Arduino with an IR transmitter, and even some packets you can send out with a  Flipper Zero. If you’re interested in learning more about the internals of this device, check out the teardown we featured back in 2019.

# Re-Creating The Unique Look Of Unobtainable Aerochrome Film

Ever heard of Aerochrome? It’s a unique type of color infrared film, originally created for the US military and designed for surveillance planes. Photos taken with Aerochrome film show trees and other vegetation in vivid reds and pinks, creating images that aren’t quite like anything else.

Sadly, Aerochrome hasn’t been made for over a decade. What’s an enterprising hacker with a fascination for this unobtainable film to do? [Joshua] resolved to recreate it as best he could, and the results look great!

Aerochrome isn’t quite the same as normal film. It is sensitive to infrared, and photos taken with it yield a kind of false color image that presents infrared as red, visible reds as greens, and greens are shown as blue. The result is a vaguely dreamy looking photo like the one you see in the header image, above. Healthy vegetation is vividly highlighted, and everything else? Well, it actually comes out pretty normal-looking, all things considered.

Why does this happen? It’s because healthy, leafy green plants strongly absorb visible light for photosynthesis, while also strongly reflecting near-infrared. This is the same principle behind the normalized difference vegetation index (NDVI), a method used since the 70s to measure live green vegetation, often from satellite imagery.

Aerochrome may be out of production, but black and white infrared film is still available. [Joshua] found that he could re-create the effect of Aerochrome with an adaptation of trichrome photography: the process of taking three identical black and white photos, each using a different color filter. When combined, the three photos (acting as three separate color channels) produce a color image.

To reproduce Aerochrome, [Joshua] takes three monochromatic photos with his infrared film, each with a different color filter chosen to match the spectral sensitivities of the original product. The result is a pretty striking reproduction of Aerochrome!

But this method does have some shortcomings. [Joshua] found it annoying to fiddle with filters between trying to take three identical photos, and the film and filters aren’t really an exact match for the spectral sensitivities of original Aerochrome. He also found it difficult to nail the right exposure; since most light meters are measuring visible light and not infrared, the exposure settings were way off. But the results look pretty authentic, so he’s counting it as a success.

We loved [Joshua]’s DIY wigglecam, and we’re delighted to see the work he put into re-creating an authentic Aerochrome. Fantastic work.