We’ve seen a number of heart rate monitoring projects on Hackaday, but [Peter’s] electrocardiography (ECG) Instructable really caught out attention.

If you’ve followed Hackaday for any period of time, you’re probably already somewhat familiar with the hardware needed to record the ECG. First, you need a high input impedance instrumentation amplifier to pick up the millivolt signal from electrical leads carefully placed on the willing subject’s body. To accomplish this, he used an AD8232 single-lead ECG module (we’ve actually seen this part used to make a soundcard-based ECG). This chip has a built-in instrumentation amplifier as well as an optional secondary amplifier for additional gain and low-pass filtering. The ECG signal is riddled with noise from mains that can be partially attenuated with a simple low-pass filter. Then, [Peter] uses an Arduino Nano to sample the output of the AD8232, implement a digital notch filter for added mains noise reduction, and display the output on a 2.8″ TFT display.

Other than the circuit itself, two things about his project really caught our attention. [Peter] walks the reader through all the different safety considerations for a commercial ECG device and applies these principles to his simple DIY setup to ensure his own safety. As [Peter] put it, professional medical electronics should follow IEC 60601. It’s a pretty bulky document, but the main tenets quoted from [Peter’s] write-up are:

1. limiting how much current can pass through the patient
2. how much current can I pass through the patient?
3. what electrical isolation is required?
4. what happens if a “component” fails?
5. how much electromagnetic interference can I produce?
6. what about a defibrillator?

[Peter] mentions that his circuit itself does not fully conform to the standard (though he makes some honest attempts), but lays out a crude plan for doing so. These include using high-valued input resistors for the connections to the electrodes and also adding a few protection diodes to the electrode inputs so that the device can withstand a defibrillator. And of course, two simple strategies you always want to follow are using battery power and placing the device in a properly shielded enclosure.

[Peter] also does a great job breaking down the electrophysiology of the heart and relates it to terms maybe a bit more familiar to non-medical professionals. Understanding the human heart might be a little less intimidating if we relate the heart to a simple voltage source like a battery or maybe even a function generator. You can imagine the ions in our cells as charger carriers that generate electrical potential energy and nerve fibers as electrical wires along which electrical pulses travel through the body.

Honestly, [Peter] has a wealth of information and tools presented in his project that are sure to help you in your next build. You might also find his ECG simulator code really handy and his low-memory display driver code helpful as well. Cool project, [Peter]!

Measuring ECG is something that is near and dear to my heart (sorry, couldn’t resist). Two of my own projects that were featured on Hackaday before I became a writer here include a biomedical sensor suite in Arduino shield form factor, and a simple ECG built around an AD623 instrumentation amplifier.

For many of us the passing of the floppy disk is unlamented, but there remains a corps of experimenters for whom the classic removable storage format still holds some fascination. The interface for a floppy drive might have required some complexity back in the days of 8-bit microcomputers, but even for today’s less accomplished microcontrollers it’s a surprisingly straightforward hardware prospect. [David Hansel] shows us this in style, with a floppy interface, software library, and even a rudimentary DOS, for the humble Arduino Uno.

The library provides functions to allow low level work with floppy disks, to read them sector by sector. In addition it incorporates the FatFS library for MS-DOS FAT file-level access, and finally the ArduDOS environment which allows browsing of files on a floppy. The pictures show a 3.5″ drive, but it also supports 5.25″ units and both DD and HD drives. We can see that it will be extremely useful to anyone working with retrocomputer software who is trying to retrieve old disks, and we look forward to seeing it incorporated in some retrocomputer projects.

Of course, Arduino owners needn’t have all the fun when it comes to floppy disks, the Raspberry Pi gets a look-in too.

According to [Dr. Tom Lehrer’s] song Pollution, “Wear a gas mask and a veil. Then you can breathe, long as you don’t inhale!” While the air quality in most of the world hasn’t gotten that bad, there is a lot of concern about long-term exposure to particulates in the air causing health problems. [Ashish Choudhary] married an Arduino with a display and a pollution sensor to give readings of the PM2.5 and PM10 levels in the air.

The sensor uses a laser diode and a photodiode to detect and count particles, while a fan moves air through the system. If you aren’t up on pollution metrics, PM2.5 is a count of very fine particles (under 2.5 microns) and PM10 is a count of particles for 10 microns. You can find a datasheet for the device online.

One thing to note is that the sensor has a finite lifespan. The datasheet claims “up to” 8,000 hours. If you ran the sensor continuously that’s not quite a year, so you might want to be judicious about how often you light up the device.

This isn’t the first time we’ve seen this particular sensor. If you want to find the exact source of a pollutant, consider this build.

Join us on Wednesday, April 21 at noon Pacific for the AVR Reverse Engineering Hack Chat with Uri Shaked!

We’ve all become familiar with the Arduino ecosystem by now, to the point where it’s almost trivially easy to whip up a quick project that implements almost every aspect of its functionality strictly in code. It’s incredibly useful, but we tend to lose sight of the fact that our Arduino sketches represent a virtual world where the IDE and a vast selection of libraries abstract away a lot of the complexity of what’s going on inside the AVR microcontroller.

While it’s certainly handy to have an environment that lets you stand up a system in a matter of minutes, it’s hardly the end of the story. There’s a lot to be gained by tapping into the power of assembly programming on the AVR, and learning how to read the datasheet and really run the thing. That was the focus of Uri Shaked’s recent well-received HackadayU course on AVR internals, and it’ll form the basis of this Hack Chat. Then again, since Uri is also leading a Raspberry Pi Pico and RP2040 course on HackadayU in a couple of weeks, we may end up talking about that too. Or we may end up chatting about something else entirely! It’s really hard to where this Hack Chat will go, given Uri’s breadth of interests and expertise, but we’re pretty sure of one thing: it won’t be boring. Make sure you log in and join the chat — where it goes is largely up to you.

Our Hack Chats are live community events in the Hackaday.io Hack Chat group messaging. This week we’ll be sitting down on Wednesday, April 21 at 12:00 PM Pacific time. If time zones have you tied up, we have a handy time zone converter.

Click that speech bubble to the right, and you’ll be taken directly to the Hack Chat group on Hackaday.io. You don’t have to wait until Wednesday; join whenever you want and you can see what the community is talking about.

Over the years, artists have been creating art depicting weapons of mass destruction, war and human conflict. But the weapons of war, and the theatres of operation are changing in the 21^st century. The outcome of many future conflicts will surely depend on digital warriors, huddled over their computer screens, punching on their keyboards and maneuvering joysticks, or using devious methods to infect computers to disable or destroy infrastructure. How does an artist give physical form to an unseen, virtual digital weapon? That is the question which inspired [Mac Pierce] to create his latest Portrait of a Digital Weapon.

[Mac]’s art piece is a physical depiction of a virtual digital weapon, a nation-state cyber attack. When activated, this piece displays the full code of the Stuxnet virus, a worm that partially disabled Iran’s nuclear fuel production facility at Natanz around 2008.

It took a while for [Mac] to finalize the plan for his design. He obtained a high resolution satellite image of the Iranian Natanz facility via the Sentinel Hub satellite imagery service. This was printed on a transparent vinyl and glued to a translucent poly-carbonate sheet. Behind the poly-carbonate layer, he built a large, single digit 16-segment display using WS2812 addressable LED strips, which would be used to display the Stuxnet code. A bulkhead USB socket was added over the centrifuge facility, with a ring of WS2812 LEDs surrounding the main complex. When a USB stick is plugged in, the Stuxnet code is displayed on the 16-segment display, one character at a time. At random intervals, the LED ring around the centrifuge building lights up spinning in a red color to indicate centrifuge failure.

The 16-segment display was built on an aluminum base plate, with 3D printed baffles to hold the LED strips. To hold the rest of the electronics, he built a separate 3D printed frame which could be added to the main art frame. Since this was too large to be printed in one piece on the 3D printer, it was split in parts, which were then joined together using embedded metal stud reinforcement to hold the parts together. Quite a nice trick to make large, rigid parts.

An Adafruit Feather M0 micro-controller board, with micro SD-card slot was the brains of the project. To derive the 5 V logic data signal from the 3.3 V GPIO output of the Feather, [Mac] used two extra WS2812 LEDs as level shifters before sending the data to the LED strips. Driving all the LEDs required almost 20 W, so he powered it using USB-C, adding a power delivery negotiation board to derive the required juice.

The Arduino code is straightforward. It reads the characters stored on the SD-card, and sends them sequentially to the 16-segment display. The circular ring around the USB bulkhead also lights up white, but at random intervals it turns red to simulate the speeding up of the centrifuges. Detecting when the USB stick gets plugged in is another nice hack that [Mac] figured out. When a USB stick is plugged in, the continuity between the shell (shield) and the GND terminal was used to trigger a GPIO input.

Cyber warfare is here to stay. We are already seeing increasing attacks on key infrastructure installations by state as well as non-state actors around the world. Stuxnet was one of the first in this growing category of malicious, weaponized code. Acknowledging its presence using such a physical representation can offer a reminder on how a few lines of software can wreak havoc just as much as any other physical weapon. Check out the brief project video after the break.

Active suspensions are almost a holy grail for cars, adding so much performance gain that certain types have even been banned from Formula 1 racing. That doesn’t stop them from being used on a wide variety of luxury and performance cars, though, as they can easily be tuned on the fly for comfort or improved handling. They also can be fitted to remote controlled cars as [Indeterminate Design] shows with this electronic servo-operated active suspension system for his RC truck.

Each of the four servos used in this build is linked to the mounting point of the existing coilover suspension on the truck. This allows the servo to change the angle that the suspension is positioned while the truck is moving. As a result, the truck has a dramatic performance enhancement including a tighter turning radius, more stability, and the capability of doing donuts. The control system runs on an Arduino with an ESP32 to enable live streaming of data, and also includes an MPU6050 to monitor the position of the truck’s frame while it is in motion.

There’s a lot going on in this build especially with regard to the control system that handles all of the servos. Right now it’s only programmed to try to keep the truck’s body relatively level, but [Indeterminate Design] plans to program several additional control modes in the future. There’s a lot of considerations to make with a system like this, and even more if you want to accommodate for Rocket League-like jumps.

It’s 2021. Everyone and their mother is filming themselves doing stuff, and a lot of it is super cool content. But since most of us have to also work the video capture devices ourselves, it can be difficult to make compelling footage with a single, stationary overhead view, especially when there are a lot of steps involved. A slider rig is a good start, but the ability to move the camera in three dimensions programmatically is really where it’s at.

[KronBjorn]’s excellent automated overhead camera assistant runs on an Arduino Mega and is operated by typing commands in the serial monitor. It can pan ±20° from straight down and moves in three axes on NEMA-17 stepper motors. It moves really smoothly, which you can see in the videos after the break. The plastic-minimal design is interesting and reminds us a bit of an ophthalmoscope — that’s that main rig at the eye doctor. There’s only one thing that would make this better, and that’s a dedicated macro pad.

If you want to build your own, you’re in luck — there’s quite a lot of detail to this project, including a complete BOM, all the STLs, code, and even assembly videos of the 3D-printed parts and the electronics. Slide past the break to check out a couple of brief demo videos.

Not enough room for a setup like this one? Try the pantograph version.

We will be the first to admit that it’s often hard to be productive while working from home, especially if no one’s ever really looking over your shoulder. Well, here is one creepy way to feel as though someone is keeping an eye on you, if that’s what gets you to straighten up and fly right. The Eyecam research project by [Marc Teyssier] et. al. is a realistic, motorized eyeball that includes a camera and hangs out on top of your computer monitor. It aims to spark conversation about the sensors that are all around us already in various cold and clinical forms. It’s an open source project with a paper and a repo and a how-to video in the works.

The eyebrow-raising design pulls no punches in the uncanny department: the eye behaves as you’d expect (if you could have expected this) — it blinks, looks around, and can even waggle its brow. The eyeball, brow, and eyelids are actuated by a total of six servos that are controlled by an Arduino Nano.

Inside the eyeball is a Raspberry Pi camera connected to a Raspi Zero for the web cam portion of this intriguing horror show. Keep an eye out after the break for the Eyecam infomercial.

Creepy or fascinating, it succeeds in making people think about the vast amount of sensors around us now, and what the future of them could look like. Would mimicking eye contact be an improvement over the standard black and gray oblong eye? Perhaps a pair of eyes would be less unsettling, we’re not really sure. But we are left to wonder what’s next, a microphone that looks like an ear? Probably. Will it have hair sprouting from it? Perhaps.

Yeah, it’s true; two eyes are more on the mesmerizing side, but still creepy, especially when they follow you around the room and can shoot frickin’ laser beams.

Thanks for the tip, [Sven, greg, and Itay]!

Multirotors, or drones as they’re popularly called, are so ubiquitous as to have become a $10 toy. They’re no less fun to fly for it though, and learning how they work is no less fascinating. It’s something [Science Buddies] has addressed in a series of videos examining them from first principles. They may be aimed at youngsters, but they’re still an entertaining enough watch for those of advancing years.

Instead of starting with a multirotor control board, the video takes four little DC motors and two popsicle sticks to make a rudimentary drone frame. Then with the help of dowels and springs it tethers the craft as the control mechanisms are explained bit by bit, from simple on-off motor control through proportional control to adding an Arduino and following through to how a multirotor stays in flight. It’s instructional and fun to watch, and maybe even for some of us, a chance to learn something.

We’ve had multirotor projects aplenty here over the years, but how about something completely different made from popsicle sticks?

With so many students attending class virtually these days, how can you give kids — or adults — some hands on experience with electronics projects? [Ben Finio] says you can by moving your lab to the virtual world using — of all things — Tinkercad. [Ben] should know something about a classroom since he is a lecturer at Cornell.

Of course, you could do this trick with any online simulator, but Tinkercad is nice because it is easy to use, looks real, and doesn’t cost the students a dime. [Ben] mentions there are some scenarios where it is especially useful like large classes or online classes. There are probably some cases where it doesn’t make sense, like teaching RF design, for example. Even then, maybe you just need a different tool.

It would be something else if Tinkercad would add some features to support this use case. Imagine an instructor being able to peek at a student’s circuit or modify it without having to screen share to the whole class. Or perhaps provide a connector to connect one student’s outputs to another student’s inputs.

We couldn’t help but think you could do some more hardcore electronics using our favorite Falstad simulator. It doesn’t have the realistic look, but it can simulate a lot of interesting circuits. After all, we’ve long been a fan of project-based learning.