Calculator Battery Mod Lets You Go The Distance

September 23, 2025 by 23 Comments

Disposable batteries seem so 1990s. Sure, it’s nice to be able to spend a couple of bucks at the drugstore and get a flashlight or TV remote back in the game, but when the device is a daily driver, rechargeable batteries sure seem to make more financial sense. Unfortunately, what makes sense to the end user doesn’t always make sense to manufacturers, so rolling your own rechargeable calculator battery pack might be your best option.

This slick hack comes to us from [Magmabow], who uses a Casio FXCG50 calculator, a known battery hog. With regular use, it goes through a set of four alkaline AA batteries every couple of months, which adds up quickly. In search of a visually clean build, [Magmabow] based the build around the biggest LiPo pillow-pack he could find that would fit inside the empty battery compartment, and planned to tap into the calculator’s existing USB port for charging. A custom PCB provides charging control and boosts the nominal 3.7-volt output of the battery to the 5-ish volts the calculator wants to see. The PCB design is quite clever; it spans across the battery compartment, with its output feeding directly into the spring contacts normally used for the AAs. A 3D-printed insert keeps the LiPo and the PCB in place inside the battery compartment.

Almost no modifications to the calculator are needed, other than a couple of bodge wires to connect the battery pack to the calculator’s USB port. The downside is that the calculator’s battery status indicator won’t work anymore since the controller will just shut the 5-volt output down when the LiPo is discharged. It seems like there might be a simple fix for that, but implementing it on such a small PCB could be quite a challenge, in which case a calculator with a little more room to work with might be nice. Continue reading “Calculator Battery Mod Lets You Go The Distance” →

Automatic Feeder Keeps Fish Sated

September 23, 2025 by 3 Comments

[Noisy Electrons] is a maker who also likes to keep fish. He sometimes needs to travel and keep his fish fed in the meantime, so he created an automated solution to handle that for him.

The build is based around an STM32 microcontroller, paired with a MCP7940N real-time clock to keep time. The microcontroller is hooked up to a few buttons and a small display to serve as an interface, allowing the feeding times and dosage amounts to be configured right on the device. Food is distributed from a 3D printed drum with a hole in it, which is rotated via a stepper motor.  Each time the drum rotates, some food falls through the hole and into the tank. Dosage amount is measured in rotations — the more times the drum rotates, the more food is delivered to the fish.

[Noisy Electron] built three of these devices for three separate tanks. Thus far, it’s been three weeks and all the fish are still alive, so we’ll take that as a vote of confidence in the build. We’ve featured some other great pet feeders over the years, too Continue reading “Automatic Feeder Keeps Fish Sated” →

2025 Hackaday Superconference: Announcing Our Workshops And Tickets

September 23, 2025 by 7 Comments

Can you feel the nip of fall in the air? That can only mean one thing: Supercon is just around the corner. The next few weeks are going to bring a blitz of Supercon-related reveals, and we’re starting off with a big one: the workshops.

Supercon is the Ultimate Hardware Conference, and you need to be there to attend a workshop. Both workshop and general admission tickets are on sale now! Don’t wait — they sell out fast.

Continue reading “2025 Hackaday Superconference: Announcing Our Workshops And Tickets” →

Moondream title with man's face visible in background.

Using Moondream AI To Make Your Pi “See” Like A Human

September 23, 2025 by 9 Comments

[Jaryd] from Core Electronics shows us human-like computer vision with Moondream on the Pi 5.

Using the Moondream visual language model, which runs directly on your Raspberry Pi, and not in the cloud, you can answer questions such as “are the clothes on the line?”, “is there a package on the porch?”, “did I leave the fridge open?”, or “is the dog on the bed?” [Jaryd] compares Moondream to an alternative visual AI system, You Only Look Once (YOLO).

Processing a question with Moondream on your Pi can take anywhere from just a few moments to 90 seconds, depending on the model used and the nature of the question. Moondream comes in two varieties, based on size, one is two billion parameters and the other five hundred million parameters. The larger model is more capable and more accurate, but it has a longer processing time — the fastest possible response time coming in at about 22 to 25 seconds. The smaller model is faster, about 8 to 10 seconds, but as you might expect its results are not as good. Indeed, [Jaryd] says the answers can be infuriatingly bad.

In the write-up, [Jaryd] runs you through how to use Moonbeam on your Pi 5 and the video (embedded below) shows it in action. Fair warning though, Moondream is quite RAM intensive so you will need at least 8 GB of memory in your Pi if you want to play along.

If you’re interested in machine vision you might also like to check out Machine Vision Automates Trainspotting With Unique Full-Length Portraits.

Continue reading “Using Moondream AI To Make Your Pi “See” Like A Human” →

The Impending CRT Display Revival Will Be Televised

September 23, 2025 by 112 Comments

Until the 2000s vacuum tubes practically ruled the roost. Even if they had surrendered practically fully to semiconductor technology like integrated circuits, there was no escaping them in everything from displays to video cameras. Until CMOS sensor technology became practical, proper video cameras used video camera tubes and well into the 2000s you’d generally scoff at those newfangled LC displays as they couldn’t capture the image quality of a decent CRT TV or monitor.

For a while it seemed that LCDs might indeed be just a flash in the pan, as it saw itself competing not just with old-school CRTs, but also its purported successors in the form of SED and FED in particular, while plasma TVs  made home cinema go nuts for a long while with sizes, fast response times and black levels worth their high sale prices.

We all know now that LCDs survived, along with the newcomer in OLED displays, but despite this CRTs do not feel like something we truly left behind. Along with a retro computing revival, there’s an increasing level of interest in old-school CRTs to the point where people are actively prowling for used CRTs and the discontent with LCDs and OLED is clear with people longing for futuristic technologies like MicroLED and QD displays to fix all that’s wrong with today’s displays.

Could the return of CRTs be nigh in some kind of format?

Continue reading “The Impending CRT Display Revival Will Be Televised” →

Heart Rate Measurement Via WiFi, The DIY Way

September 23, 2025 by 13 Comments

A few weeks back, we reported on a research group that figured out how to measure heartrate using perturbations in WiFi signals. [Nick Bild] was interested in this so-called “Pulse-Fi” technique, but noted the paper explaining it was behind a paywall. Thus, he worked to recreate the technology himself so he could publish the results openly for anyone eager to learn.

[Nick] paid for the research paper, and noted that it was short on a few of the finer details and didn’t come with any code or data from the original research team. He thus was left to figure out the finer details of how to measure heart rate via WiFi in his own way, though he believes his method is quite close to the original work.

The basic concept is simple enough. One ESP32 is set up to transmit a stream of Channel State Information packets to another ESP32, with a person standing in between. As the person’s heart beats, it changes the way the radio waves propagate from the transmitting unit to the receiver. These changes can be read from the packets, and processed to estimate the person’s heart rate. [Nick] explains the various data-massaging steps involved to go from this raw radio data to a usable heart rate readout.

It’s a great effort from [Nick] to recreate this research all on his own in his home lab. Files are on GitHub for the curious. If you’re eager to learn more about these innovative measurement techniques, you might like to read our prior reporting on the tech. Also, it’s worth remembering—don’t use your homebrew prototypes for any serious healthcare purposes. Continue reading “Heart Rate Measurement Via WiFi, The DIY Way” →

Play Capacitor Cupid With The Matchmaker

September 23, 2025 by 5 Comments

Occasionally a design requires capacitors that are much closer to being identical in value to one another than the usual tolerance ranges afford. Precision matching of components from parts on hand might sound like a needle-in-a-haystack problem, but not with [Stephen Woodward]’s Capacitor Matchmaker design.

The larger the output voltage, the greater the mismatch between capacitors A and B.

The Matchmaker is a small circuit intended to be attached to a DVM, with the output voltage indicating whether two capacitors (A and B) are precisely matched in value. If they are not equal, the voltage output indicates the degree of the mismatch as well as which is the larger of the two.

The core of the design is complementary excitation of the two capacitors (the CD4013B dual flip-flop achieves this) which results in a measurable signal if the two capacitors are different; nominally 50 mV per % of mismatch. Output polarity indicates which of the capacitors is the larger one. In the case of the two capacitors being equal, the charges cancel out.

Can’t precision-matched capacitors be purchased? Absolutely, but doing so is not always an option. As [Stephen] points out, selection of such components is limited and they come at an added cost. If one’s design requires extra-tight tolerances, requires capacitor values or types not easily available as precision pairs, or one’s budget simply doesn’t allow for the added cost, then the DIY approach makes a lot more sense.

If you’re going to go down this road, [Stephen] shares an extra time-saving tip: use insulated gloves to handle the capacitors being tested. Heating up a capacitor before testing it — even just from one’s fingers — can have a measurable effect.

[Stephen]’s got a knack for insightful electronic applications. Check out his PWMPot, a simple DIY circuit that can be an awfully good stand-in for a digital potentiometer.