Weird Things To Do With FPGAs

March 21, 2024 by Al Williams 5 Comments

There’s an old joke about how can you find the height of a building using a barometer. One of the punchlines is to drop the barometer from the roof and time how long it takes to hit the ground. We wonder if [Alexlao512] had that in mind when he wrote a post about unconventional uses of FPGAs. Granted, he isn’t dropping any of them off a roof, but still. The list takes advantage of things we usually try to avoid such as temperature variation, metastability, and the effects of propagation delays.

For example, you probably know that hooking up an odd number of inverters into a loop forms an oscillator—the so-called ring oscillator. The post discusses how you can use an oscillator like that to measure propagation delay or even as a strain gauge. If you put pressure on the FPGA chip, the frequency of the ring oscillator will subtly vary.

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PentaBlinky – When One LED Is Not Blinky Enough

August 10, 2023 by Dave Rowntree 4 Comments

[michimartini] over on Hackaday.io loves playing with multivibrator circuits, and has come across a simple example of a ring oscillator. This is a discrete transistor RC-delay design utilizing five identical stages, each of which has a transistor that deals with charging and discharging the timing capacitor, passing along the inverted signal to its nearest neighbor. The second transistor isn’t strictly needed and is only there to invert the signal in order to drive the LED. When the low pulse passes by the LED lights, without it you’d see all the LEDs lit bar one, which doesn’t look as good.

Compare this with an astable multivibrator to understand how it works

Essentially this circuit is just the classic astable multivibrator circuit that has been split in half and replicated so that the low pulse propagates through more stages than just the two, but thinking about it as a single stage doesn’t work so well until you draw in a couple of neighbors to help visualize the behavior better.

[michimartini] does lament that the circuit starts up in a chaotic fashion and needs a quick short applying to one transistor element in order to get it to settle into a steady rhythm. Actually, that initial behaviour could be interesting in itself, especially as the timing changes with voltage and temperature.

Anyway, we like the visual effect and the curvy organic traces. It would make a neat pin badge. Since we’re thinking about blinkies, here are couple of somewhat minimalist attempts, the world’s smallest blinky, and an even smaller one. Now, who doesn’t love this stuff?

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NE555-Based Electronic Dice

December 11, 2022 by Dave Walker 14 Comments

It has become a bit of a running joke in the Hackaday community to suggest that a project could or should have been done with a 555 timer. [Tim] has rather taken this to heart with his latest Electronic Dice project, which uses three of the venerable devices.

If three seems like a lot of 555s to make an electronic die, then it may be worth considering that the last time we shared his project he was using 22 of them! Since then, [Tim] has been busy optimising his design, whilst keeping within the constraints of an old-school through-hole soldering kit.

Maybe the most surprising thing about this project is the purpose to which the NE555 devices are pressed. Rather than using them for their famous oscillation properties, they are in actual fact just being used as Schmitt Triggers to clean up the three-phase ring oscillator that is constructed from discrete transistors and passives.

scope trace of the electronic dice ring oscillator — Simulation trace of the three-phase ring oscillator before Scmitt Trigger stages

The ring oscillator cleverly produces three phase-shifted square waves such that a binary combination of the three phases offers six unique states. Six being the perfect number for a dice throw, all that then remains is to figure out which LEDs need to be switched on in which state and wire them up accordingly.

To “roll” the dice, a push-button powers up the oscillator, and stops it again when it is released, displaying the random end-state on the LEDs.

It can be fun to see what can be done using old technology, and educational to try to optimise a design down to the fewest parts possible.

[Tim]’s earlier project is here if you want to see how the design has evolved. The documentation on both of these iterations is excellent and well worth a read.

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Solar Heart Engineered To Beat For Decades

December 6, 2018 by Tom Nardi 5 Comments

It’s often said that if something is worth doing it’s worth doing right, or maybe even worth overdoing. This is clearly a concept that [ANTALIFE] takes very seriously, as made abundantly clear by projects like the solar powered “beating” heart he made as a gift for his wife. What for most of us would have ended up being a junk bin build becomes a considerable engineering project in his hands, with a level of research and fine tuning that’s frankly staggering.

But [ANTALIFE] didn’t put this much thought into the device just for fun. He wants it to remain functional for as long as 30 years, and hopes he and the missus can still look on it fondly in their retirement years. Keeping an electronic device up and running for decades straight means you need to look carefully at each component and try to steer clear of any potential pitfalls.

The biggest one was the battery. More specifically, the fact he couldn’t use one. The lifetime of most rechargeable batteries is measured in hundreds of cycles, which for a device which will be charged by solar every day, means the battery is going to start showing its age in only 4 to 5 years. That simply wasn’t going to cut it.

[ANTALIFE] did some digging and realized that the solution was to use a supercapacitor, specifically the AVX SCMS22C255PRBA0. This is little wonder is rated for a staggering half million cycles, which in theory means that even with daily use it should still take a charge in the year 3300. In practice of course there are a lot of variables which will reduce that lifetime such as temperature fluctuations and the Earth being conquered by apes; but no matter what caveats you put on the figure it should still make 30 years without breaking a sweat.

Similar thought was given to choosing a solar cell with a suitably long lifetime, and he did plenty of testing and experimentation with his charging circuit, including some very nice graphs showing efficiency over time, to make sure it was up to snuff. Finally he walks the reader though his light-sensitive ring oscillator circuit which gives the device its pleasing “breathing” effect once the lights go down.

We’d love to bring you an update on this device in 30 years to see how close [ANTALIFE] got, but as we’re still trying to work the kinks out of the mobile version of the site we can’t make any guarantees about what the direct-brain interface version of HaD might look like. In the meantime though, you can read up on the long term battle between supercapacitors and traditional batteries.

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How The 8087 Coprocessor Got Its Bias

August 18, 2018 by Steven Dufresne 8 Comments

Most of us have been there. You build a device but realize you need two or more voltages. You could hook up multiple power supplies but that can be inconvenient and just not elegant. Alternatively, you can do something in the device itself to create the extra voltages starting with just one. When [Ken Shirriff] decapped an 8087 coprocessor to begin exploring it, he found it had that very problem. It needed: +5 V, a ground, and an additional -5 V.

His exploration starts with a smoking gun. After decapping the chip and counting out all the bond wires going to the various pads, he saw there was one too many. It wasn’t hard to see that the extra wire went to the chip’s substrate itself. This was for providing a negative bias to the substrate, something done in some high-performance chips to get increased speed, a more predictable transistor threshold voltage, and to reduce leakage current. Examining where the bond wire went to in the circuitry he found the two charge pump circuits shown in the banner image. Those worked in alternating fashion to supply a -5 V bias to the substrate, or rather around -3 V when you take into account voltage drops. Of course, he also explains the circuits and dives in deeper, including showing how the oscillations are provided to make the charge pumps work.

If this is anything like [Ken’s] previous explorations, it’ll be the first of a series of posts exploring the 8087. At least that’s what we hope given how he’d previously delighted us with a reverse engineering of the 76477 sound effects chip used in Space Invaders and then went deeper to talk about integrated injection logic (I²L) as used in parts of the chip.

Living Logic: Biological Circuits For The Electrically Minded

August 21, 2017 by Michael Uttmark 18 Comments

Did you know you can build fundamental circuits using biological methods? These aren’t your average circuits, but they work just like common electrical components. We talk alot about normal silicon and copper circuits ‘roud here, but it’s time to get our hands wet and see what we can do with the power of life!

In 1703, Gottfried Wilhelm Leibniz published his Explication de l’Arithmétique Binaire (translated). Inspired by the I Ching, an ancient Chinese classic, Leibniz established that the principles of arithmetic and logic could be combined and represented by just 1s and 0s. Two hundred years later in 1907, Lee De Forest’s “Audion” is used as an AND gate. Forty years later in 1947, Brattain and H. R. Moore demonstrate their “PNP point-contact germanium transistor” in Bell Labs (often given as the birth date of the transistor). Six years later in 1953, the world’s first transistor computer was created by the University of Manchester. Today, 13,086,801,423,016,741,282,500¹ transistors have built a world of progressing connectivity, automation and analysis.

While we will never know how Fu Hsi, Leibniz, Forest or Moore felt as they lay the foundation of the digital world we know today, we’re not completely out of luck: we’re in the midst’s of our own growing revolution, but this one’s centered around biotechnology. In 1961, Jacob and Monod discovered the lac system: a biological analog to the PNP transistor presented in Bell Labs fourteen years earlier. In 2000, Gardner, Cantor, and Collins created a genetic toggle switch controlled by heat and a synthetic fluid bio-analog². Today, AND, OR, NOR, NAND, and XOR gates (among others) have been successfully demonstrated in academic labs around the world.

But wait a moment. Revolution you say? Electrical transistors went from invention to computers in 6 years, and biological transistors went from invention to toggle button in 40? I’m going to get to the challenges facing biological circuits in time, but suffice it to say that working with living things that want to be fed and (seem to) like to die comes with its own set of challenges that aren’t relevant when working with inanimate and uncaring transistors. But, in the spirit of hacking, let’s dive right in. Continue reading “Living Logic: Biological Circuits For The Electrically Minded” →

Afroman Makes A UHF Oscillator From A Potato

April 30, 2017 by Jenny List 18 Comments

If you have ever worked with simple logic gates, there is a good chance that at some point you will have built a ring oscillator from a chain of inverters. With the addition of a resistor and a capacitor, you can easily make a square wave oscillator up into the megahertz range with standard logic chips.

[Afroman] received some rather special logic chips, from an unexpectedly named company, Potato Semiconductor. They specialise in making versions of common 74 series logic that smash the usual 100+ MHz barrier of the faster conventional 74 series chips, and extend their bandwidth up to over 1 GHz. Using one of their 74GU04 parts, he made a ring oscillator relying only on the stray capacitances of its gate inputs for its timing, and while he didn’t manage to achieve a GHz he did measure it at about 373 MHz. He took a look with a spectrum analyser, and as you might expect from a logic circuit found strong harmonics in the GHz range.

Now normally there would be no news in someone making a ring oscillator with a 7404. It really wouldn’t be a hack with a run-of-the-mill 74LS or 74HC part. But this Potato part is sufficiently unusual that it deserves a bit of attention in its own right. After all, we’re not used to logic chips that can work at those kinds of frequencies.

We’ve put his video below the break. Meanwhile, the Potato Semiconductor website makes for an interesting browse, and proves that there is plenty of life left in the venerable 74 series.

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