Light Emitting Logic Gates Built From Scratch

October 24, 2019 by Sharon Lin 44 Comments

What’s the weirdest computer you can think of? This one’s weirder.

[Dr. Cockroach] figured out a way to create an inverting NOT gate from just one LED and two resistors (one being a photo-resistor). The Dr. has since built AND, NAND, OR, NOR, XOR and XNOR gates, as well as a buffer, incorporating light into every logic gate.

Traditional inverters – NOT gates – are already made with diodes (typically not light-emitting), resistors (typically not light-dependent), and bipolar transistors. The challenge was to reduce the number of transistors. The schematic from the very first test shows the slight modifications [Dr. Cockroach] made to incorporate light into the logic gate using a 910 Ohm, output LED, and an LED and LDR in parallel.

The output is initially 4.5V for logic 1 and 1.5V for logic 0. Adding two 1N914 diodes and an AND gate ahead of the inverter create a two-input NAND gate. With the two diodes reversed and a 910 Ohm resistor removed, a NOR gate is created.

The next step was to build a S-R latch using the NAND gates and inverters, which holds some basic memory. From there, with some size reductions, a Master-Slave J-K Flip Flop, similarly using NAND gates and inverters, can be built. The current state of the project is a working sequencer and counter. You can even see a smooth sine wave propagating through the LED chaser, which is typically built with ICs or transistors but in this case is built simply with LEDs, LDRs, resistors, and capacitors.

The upcoming plan is to use the gates to build a processor that only uses diodes, resistors, and capacitors. While it’s probably not going to be nearly as fast as any processors we have today, it should be interesting (and educational!) to be able to visually track the flow of data from one logic gate over to the next. Continue reading “Light Emitting Logic Gates Built From Scratch” →

Shedding A Bit Of Light On Some Logic

October 15, 2018 by Jenny List 30 Comments

When it comes to logic technologies, we like to think we’ve seen them all here at Hackaday. But our community never ceases to surprise us with its variety and ingenuity, so it should be a surprise that [Dr Cockroach] has delivered one we’ve not seen before. Light logic doesn’t use the conventional active devices you’d expect such as transistors, tubes, or even relays. Instead, it uses LEDs and CdS cells to make rudimentary switches. So far there is a NAND, a NOR, and a set-reset latch that appears in the video below the break, and it is not inconceivable that much more complex devices could be crafted.

The CdS cell switch is not too far different in operation to a transistor, with the CdS cell forming half of a potential divider as a rough equivalent of a collector-emitter circuit, and the LED feeding its light to the cell and forming a rough equivalent of a base circuit. It would probably not form a very good analog of a transistor and it seems likely that is will not be the fastest of devices, but we applaud the ingenuity in coming up with it.

CdS cells are a component that seems almost to come from another era, redolent of childhood electronic kits from days of yore. It’s no surprise we don’t see them too often, though, they pop up in the occasional automatic sunglasses.

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Cranking Up The Detail In A Flight Simulator From 1992

December 5, 2024 by Tom Nardi 22 Comments

Nostalgia is a funny thing. If you experienced the early days of video games in the 1980s and 90s, there’s a good chance you remember those games looking a whole lot better than they actually did. But in reality, the difference between 2023’s Tears of the Kingdom and the original Legend of Zelda is so vast that it can be hard to reconcile the fact that they’re both in the same medium. Of course, that doesn’t mean change the way playing those old games actually makes you feel. If only there was some way to wave a magic wand and improve the graphics of those old titles…

Well, if you consider Ghidra and a hex editor to be magic wands in our community, making that wish come true might be more realistic than you think. As [Alberto Marnetto] explains in a recent blog post, decompiling Stunt Island and poking around at the code allows one to improve the graphical detail level in the flight simulator by approximately 800%. In fact, it’s possible to go even higher, though at some point the game simply becomes unplayable.

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Boss Byproducts: Fulgurites Are Fossilized Lightning

October 29, 2024 by Kristina Panos 28 Comments

So far in this series, we’ve talked about man-made byproducts — Fordite, which is built-up layers of cured car enamel, and Trinitite, which was created during the first nuclear bomb test.

A fulgurite pendant. — A lovely fulgurite pendant. Image via Etsy

But not all byproducts are man-made, and not all of them are basically untouchable. Some are created by Mother Nature, but are nonetheless dangerous. I’m talking about fulgurites, which can form whenever lightning discharges into the Earth.

It’s likely that even if you’ve seen a fulgurite, you likely had no idea what it was. So what are they, exactly? Basically, they are natural tubes of glass that are formed by a fusion of silica sand or rock during a lightning strike.

Much like Lichtenberg figures appear across wood, the resulting shape mimics the path of the lightning bolt as it discharged into the ground. And yes, people make jewelry out of fulgurites.

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Mechanical Logic Gates With Amplification

September 20, 2024 by Bryan Cockfield 5 Comments

One of the hardest things about studying electricity, and by extension electronics, is that you generally can’t touch or see anything directly, and if you can you’re generally having a pretty bad day. For teaching something that’s almost always invisible, educators have come up with a number of analogies for helping students understand the inner workings of this mysterious phenomenon like the water analogy or mechanical analogs to electronic circuits. One of [Thomas]’s problems with most of these devices, though, is that they don’t have any amplification or “fan-out” capability like a real electronic circuit would. He’s solved that with a unique mechanical amplifier.

Digital logic circuits generally have input power and ground connections in addition to their logic connection points, so [Thomas]’s main breakthrough here is that the mechanical equivalent should as well. His uses a motor driving a shaft with a set of pulleys, each of which has a fixed string wrapped around the pulley. That string is attached to a second string which is controlled by an input. When the input is moved the string on the pulley moves as well but the pulley adds a considerable amount of power to to the output which can eventually be used to drive a much larger number of inputs. In electronics, the ability to drive a certain number of inputs from a single output is called “fan-out” and this device has an equivalent fan-out of around 10, meaning each output can drive ten inputs.

[Thomas] calls his invention capstan lever logic, presumably named after a type of winch used on sailing vessels. In this case, the capstan is the driven pulley system. The linked video shows him creating a number of equivalent circuits starting with an inverter and working his way up to a half adder and an RS flip-flop. While the amplifier pulley does take a minute to wrap one’s mind around, it really helps make the equivalent electronic circuit more intuitive. We’ve seen similar builds before as well which use pulleys to demonstrate electronic circuits, but in a slightly different manner than this build does.

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Responsive LCD Backlights With A Little Lateral Thinking

July 3, 2024 by Jenny List 23 Comments

LCD televisions are a technological miracle, but if they have an annoying side it’s that some of them are a bit lacklustre when it comes to displaying black. [Mousa] has a solution, involving a small LCD and a bit of lateral thinking.

These screens work by the LCD panel being placed in front of a bright backlight, and only letting light through at bright parts of the picture. Since LCD isn’t a perfect attenuator, some of the light can make its way through, resulting in those less than perfect blacks. More recent screens replace the bright white backlight with an array of LEDs that light up with the image, but the electronics to make that happen are not exactly trivial.

The solution? Find a small LCD panel and feed it from the same HDMI source as a big panel. Then place an array of LDRs on the front of the small LCD, driving an array of white LEDs through transistor drivers to make a new responsive backlight. We’re not sure we’d go to all this trouble, but it certainly looks quite cool as you can see below the break.

This may be the first responsive backlight we’ve brought you, but more than one Ambilight clone has graced these pages.

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Logic Analyzers: Decoding And Monitoring

April 15, 2024 by Arya Voronova 8 Comments

Last time, we looked into using a logic analyzer to decode SPI signals of LCD displays, which can help us reuse LCD screens from proprietary systems, or port LCD driver code from one platform to another! If you are to do that, however, you might find a bottleneck – typically, you need to capture a whole bunch of data and then go through it, comparing bytes one by one, which is quite slow. If you have tinkered with Pulseview, you probably have already found an option to export decoded data – all you need to do is right-click on the decoder output and you’ll be presented with a bunch of options to export it. Here’s what you will find:

2521888-2521888 I²C: Address/data: Start 2521896-2521947 I²C: Address/data: Address write: 22 2521947-2521954 I²C: Address/data: Write 2521955-2521962 I²C: Address/data: ACK 2521962-2522020 I²C: Address/data: Data write: 01 2522021-2522028 I²C: Address/data: ACK 2522030-2522030 I²C: Address/data: Start repeat 2522038-2522089 I²C: Address/data: Address read: 22 2522089-2522096 I²C: Address/data: Read 2522096-2522103 I²C: Address/data: ACK 2522104-2522162 I²C: Address/data: Data read: 91 2522162-2522169 I²C: Address/data: NACK 2522172-2522172 I²C: Address/data: Stop

Whether on the screen or in an exported file, the decoder output is not terribly readable – depending on the kind of interface you’re sniffing, be it I2C, UART or SPI, you will get five to ten lines of decoder output for every byte transferred. If you’re getting large amounts of data from your logic analyzer and you want to actually understand what’s happening, this quickly will become a problem – not to mention that scrolling through the Pulseview window is not a comfortable experience.

The above output could look like this: 0x22: read 0x01 ( DEV_ID) = 0x91 (0b10010001). Yet, it doesn’t, and I want to show you how to correct this injustice. Today, we supercharge Pulseview with a few external scripts, and I’ll show you how to transfer large amounts of Sigrok decoder output data into beautiful human-readable transaction printouts. While we’re at it, let’s also check out commandline sigrok, avoiding the Pulseview UI altogether – with sigrok-cli, you can easily create a lightweight program that runs in the background and saves all captured data into a text file, or shows it on a screen in realtime! Continue reading “Logic Analyzers: Decoding And Monitoring” →