Partial Relay-Based Calculator Puts The Click Where It Counts

November 3, 2023 by Dan Maloney 15 Comments

It looks like [Michal Zalewski] is raising the next generation the right way. First, his eldest son asks for help building a one-bit computer from discrete transistors. Not to be left behind, his little brother then asked for help with an even more retro project, which resulted in this partially relay-based calculator. Maybe there is some hope for the future.

Now, purists will no doubt notice the ATmega64 microcontroller sitting in the middle of the main PCB on this project and cry “Foul!” But perfect is the enemy of done, and as [Michal] explains, at $6 a pop for the Omron relays he and his son chose, there’s only so far you can go with relay logic before you’re taking out a second mortgage. So the relays are limited to the ALU of the calculator, along with the drivers for the six seven-segment LED displays. The microcontroller is just there for housekeeping functions like scanning the keyboard and decoding digits. All the actual calculations are in the relay logic, not silicon. And we’d be remiss not to praise his son’s stylistic choices for this design — that it uses relays with clear covers, and that it has ~~single-sided~~ PCBs with curvy, ~~hand-drawn traces~~ traces that look hand-drawn on old-school yellow substrate. [Michal]’s heart must swell with pride to have fathered someone with such exquisite taste.

For his part, [Mikal] did some really good documentation for this build, including excellent descriptions of Boolean math with half- and full-adders and how relays are used to create the basic logic gates that comprise them. The calculator itself is still a work in progress, with microcontroller code still in development, but it’s working enough that you can enjoy the display driver’s clickiness in the video below. If that doesn’t do it for you, we’ve got other relay calculators to scratch that click itch. Continue reading “Partial Relay-Based Calculator Puts The Click Where It Counts” →

Random Number Generator Is A Blast From The Past

November 2, 2023 by Tom Nardi 16 Comments

Hackers love random numbers, or more accurately, the pursuit of them. It turns out that computers are so good at following our exacting instructions that they are largely incapable of doing anything that would fit the strict definition of randomness — which has lead to some elaborate methods of generating the unexpected.

Admittedly, the SB42 Random Number Generator built by [Simon Boak] isn’t exactly something you’d be using for cryptography. The method used to generate the digits, a pair of 555 timers sending pulses through linear-feedback shift registers, would at best be considered pseudo-random. Plus the only way of getting the digits out of the machine is by extracting them from the Nixie tubes with your Mark I Eyeballs. But it absolutely excels at the secondary reason many hackers like to build their own randomness rigs — it looks awesome.

Externally, it absolutely nails the look of a piece of vintage DIY year. Down to the classic white-on-black label tape. But open up the hood, and you’re treated to a real rarity these days: wirewrap construction. In an era where you can get PCBs made and shipped to your door for literally pennies, [Simon] is out there keeping the old ways alive. It doesn’t just look the part either. Unlike most modern projects we see, there isn’t a multi-core microcontroller behind the scenes doing all the work, it’s logic gates all the way down.

This isn’t the first random-ish number generator that we’ve seen use shift registers. But if you’re looking for something that might actually pass some randomness checks, and don’t mind working with something a bit spicy, you could check out some of the previous devices we’ve covered that used radioactive decay as an entropy source.

Continue reading “Random Number Generator Is A Blast From The Past” →

Make Your Own 1970s Magnetic Stripe Cards

October 25, 2023 by Jenny List 8 Comments

We’re now all used to near-limitless storage on flash and other semiconductor technologies, but there was a time when persistent storage was considerably less easy to achieve. A 1970s programmable calculator from Sharp approached the problem with magnetic strips on special cards, and since [Menadue] has one with no cards, he set about making his own.

These cards are a little different to the credit-card-style cards we might expect, instead they’re a narrow strip with a magnetic stripe down their centre. The unusual feature can be found at the edge, where a row of perforations provide the equivalent of a clock line.

The newly manufactured cards have the clock slots machined along their edges, and then the magnetic part formed from self-adhesive magnetic strip. This last thing is a product we were not aware existed, and can think of plenty of possible applications.

The result as you can see in the video below the break are some cards with variable reliability. There’s a suggestion that white cards might work less well with the infrared light used in the clock detector, also a suspicion the low batteries make reading less easy, but still he’s able to retrieve a stored program. An extinct medium is revived.

Longtime readers will know we’ve spent time in calculator country before.

Continue reading “Make Your Own 1970s Magnetic Stripe Cards” →

Converting A Polaroid SX70 Camera To Use 600 Film

October 20, 2023 by Lewin Day 4 Comments

These days, it’s possible to buy a number of different Polaroid instant cameras new off the shelf. That’s largely thanks to the retro resurgence that has buoyed interest in everything from vinyl records to analog synthesizers. However, if you’re truly old-school, you might still be rocking a vintage Polaroid SX-70 camera. Thankfully, there’s a way to convert these old rigs to work properly with the more popular modern 600 film.

The interesting thing about the SX-70 camera design is that its shutter speed and aperture setting are essentially linked together as the aperture and shutter assembly are combined into one unit with a variable tear-drop shaped opening. Thus, the timing of the shutter opening and closing and the extent to which it opens are what determines exposure and aperture.

Thankfully, [Jake Bright] has learned a lot about these unique cameras and exactly how this complex system operates. He shares his tips on firstly restoring the camera to factory-grade operation, and then the methods in which they may be converted to work with modern film. Fundamentally, it’s about changing capacitors or resistors to change the shutter/aperture timing. However, do it blindly and you’ll have little success. You first need to understand the camera’s mechanics, pneumatics, and its “Electric Eye” control system before you can get things dialed in just so.

We’ve seldom seen such a great deep dive into a camera outside of full-fat engineering documentation. [Jake] should be commended on his deep understanding and command of these fine instant cameras from yesteryear. May the Polaroid picture never die. Video after the break. Continue reading “Converting A Polaroid SX70 Camera To Use 600 Film” →

Spinning Up A New Laundry Monitor

October 20, 2023 by Kristina Panos 17 Comments

For all that modern washers and dryers do, they don’t let you know when they’re finished. Or they do, but it’s only a short victory song that plays once and can be easy to miss. What most of us need is a gentle reminder that there’s damp laundry festering in the washer, or fresh laundry in the dryer getting wrinkly.

This laundry monitor from [Sparks and Code] is version 2.0. The first version was working fine, but it was based on vibration (or lack thereof). Fast forward a few years, and [Sparks and Code] got a modern pair that’s so finely tuned, it doesn’t produce enough vibration to register. Back to the drawing board [Sparks and Code] went, and eventually came up with version 2.0.

Now, [Sparks and Code] is detecting whether the machines are on using a pair of split-core transformers to monitor power at the breaker box. With these, you just run the wire through the hole, and it gives the relative mV value going through the wire on a 3.5mm cable. Those cables are connected to an ESP32 inside the 3D-printed box, which is mounted above the cabinet door. Since [Sparks and Code] already has home assistants all over the house, it was easy to integrate and have them all play the message ‘please flip the laundry’.

Once this project was all buttoned up, they thought of one issue — the self-cleaning cycle. Since it takes about four hours, they like to run it overnight. You can see the problem here — no one wants to hear Alexa at 3AM. Fortunately, [Sparks and Code] was able to adjust the Python script to ignore these events. Be sure to check out the build video after the break.

If only the dryer could empty itself and fold the clothes. Oh wait, there’s a robot for that.

Continue reading “Spinning Up A New Laundry Monitor” →

This 3D Printable Soldering Air Filter Really Sucks

October 14, 2023 by Kristina Panos 24 Comments

If you solder (and we know you do), you absolutely need ventilation, even for that lead-free stuff. Fortunately, [tinyboatproductions] has gotten into air quality lately and is here to help you with their snappy 3D printed air-filtering design.

At the heart of this build is a 120 mm notoriously-quiet Noctua fan coupled with a carbon filter. It does what you’d think — position the fan the right way and it sucks the air through the filter, which catches all those nasty particles.

The only problem is that the Noctua uses PWM, so there’s no governing it with a just potentiometer. To get around this, [tinyboatproductions] introduced an Arduino Nano and a buck converter, both of which were admittedly a bit overkill. Now the speed can be controlled with a pot.

Once control of the fan was sorted, [tinyboatproductions] decide to add an OLED display to show the fan speed and power condition, which is a nice touch. Be sure to check out the build video after the break.

If this doesn’t have quite enough features for you, here’s one that’s battery powered.

Continue reading “This 3D Printable Soldering Air Filter Really Sucks” →

Teletext In Ireland, Another Broadcasting Leftover Bites The Dust

October 13, 2023 by Jenny List 14 Comments

Over the years we’ve reported on the passing of a few of the broadcasting technologies of yesteryear, such as analogue TV in America, or AM radio in Europe. Now it’s the turn of an early digital contender, as one of the few remaining holdouts of old-style teletext is to shut down its service. The Irish broadcaster RTÉ is to turn off its teletext service Aertel, which has been live in some form continuously since 1986.

Like all European countries, Ireland has had only digital TV for quite a few years now. The linked RTÉ piece implies that the Aertel service has been carried as the old-style data in the frame blanking period even when part of a digital multiplex rather than the newer digital teletext system, so we’d be really grateful if some of our Irish readers could flick on their TVs and confirm that.

In an internet-connected world it seems quaint that a limited set of curated pages could once have been such a big deal, but it’s easy to forget that for many the teletext system provided their first ever taste of online information. As it shuffles away almost unnoticed we won’t miss counting through the page numbers cycling by in the top corner as we waited for our page to load, but it’s worth marking its final passing from one of the few places it could still be found.

Teletext does pop up in a few projects here, most recently as the display engine for a game of DOOM.