IBIS Models Explained

If you’ve worked with circuit simulation, you may have run into IBIS models. The acronym is input/output buffer information, and while you can do a lot without having to deal with IBIS, knowing about it can help you have a successful simulation.

IBIS is an industry-standard format that uses ASCII text to describe voltage versus current and voltage versus time about some device’s digital input and output pins. This allows precise simulation without revealing the device’s internals, which is important to some vendors. The first post of this two-part series talks about what IBIS is and how it got started. The second part explains creating and using LTSpice to create your own IBIS models. It also covers why you might want to do that.

Of course, if you don’t care about revealing the internals of a device, you could just create a Spice simulation. However, many tools will accept both models, so it is useful to know how to produce either kind of model. In fact, to create an IBIS model, you’ll want to use a Spice model to generate the data for the IBIS model, so it is a good bet you’ll have both, even if you choose to only publish the IBIS models.

If you need a refresher on Spice, we have a series. If you prefer using something different, try Micro-Cap 12, which was commercial, but went free a few years ago.

Create Your RTL Simulations With KiCAD

[Bob Alexander] is in the process of designing a homebrew discrete TTL CPU, and wanted a way to enter schematics for digital simulations via a Verilog RTL flow. Since KiCAD is pretty good at handling hierarchical schematics, why not use that? [Bob] created a KiCAD plugin, KiCadVerilog allowing one to instantiate and wire up the circuits under consideration, and then throw the resulting Verilog file at your logic simulator of choice.

KiCadVerilog doesn’t do all the hard work though, as it only provides the structure and the wiring of the circuit. The actual guts of each TTL instance needs to be provided, and a reference to it is manually added to the schematic object fields. That’s a one-time deal, as you can re-use the component library once generated. Since TTL logic has been around for a little while, locating a suitable Verilog library for this is easy. Here’s ice-chips-verilog by [TimRudy] on GitHub for starters. It’s intended as a collection for Icestudio (which is also worth a look). Still, the Verilog code for many TTL series devices is presented ready for the taking, complete with individual test benches in case you need them.

Check out the project GitHub page for the module source code, and some more documentation about the design process.

We’ve seen many RTL hacks over the years, here’s an interesting way to generate a PCB layout with discrete logic, direct from the RTL.

Simulating Temperature In VR Apps With Trigeminal Nerve Stimulation

Virtual reality systems are getting better and better all the time, but they remain largely ocular and auditory devices, with perhaps a little haptic feedback added in for good measure. That still leaves 40% of the five canonical senses out of the mix, unless of course this trigeminal nerve-stimulating VR accessory catches on.

While you may be tempted to look at this as a simple “Smellovision”-style olfactory feedback, the work by [Jas Brooks], [Steven Nagels], and [Pedro Lopes] at the University of Chicago’s Human-Computer Integration Lab is intended to provide a simulation of different thermal regimes that a VR user might experience in a simulation. True, the addition to an off-the-shelf Vive headset does waft chemicals into the wearer’s nose using three microfluidics pumps with vibrating mesh atomizers, but it’s the choice of chemicals and their target that makes this work. The stimulants used are odorless, so instead of triggering the olfactory bulb in the nose, they target the trigeminal nerve, which also innervates the lining of the nose and causes more systemic sensations, like the generalized hot feeling of chili peppers and the cooling power of mint. The headset leverages these sensations to change the thermal regime in a simulation.

The video below shows the custom simulation developed for this experiment. In addition to capsaicin’s heat and eucalyptol’s cooling, the team added a third channel with 8-mercapto-p-menthan-3-one, an organic compound that’s intended to simulate the smoke from a generator that gets started in-game. The paper goes into great detail on the various receptors that can be stimulated and the different concoctions needed, and full build information is available in the GitHub repo. We’ll be watching this one with interest.

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Hack Your Engine Virtually

It is no secret that we like simulating circuits before we build something and there are plenty of great tools for that. But what about those of us who work on cars? Well, you might try engine-sim which is a real-time internal combustion engine simulation. Honestly, the program freely admits that it isn’t accurate enough to do engineering or engine tuning. But on the plus side, it has audio output and is at least good as an educational tool to show an engine running and how different parameters might affect it. You can see a video of the tool below.

[Ange-Yaghi] mentions that the code was primarily to power the YoutTube demo. However, the Readme hints that it might be better — or at least different — and collaboration to make it better is welcome.

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Microsoft’s New Simulator Helps Train Drone AIs

Testing any kind of project in the real world is expensive. You have to haul people and equipment around, which costs money, and if you break anything, you have to pay for that too! Simulation tends to come first. Making mistakes in a simulation is much cheaper, and the lessons learned can later be verified in the real world. If you want to learn to fly a quadcopter, the best thing to do is get some time behind the sticks of a simulator before you even purchase anything with physical whirly blades.

Oddly enough, the same goes for AI. Microsoft built a simulation product to aid the development of artificial intelligence systems for drones by the name of Project AirSim. It aims to provide a comprehensive environment for the testing of drone AI systems, making development faster, cheaper, and more practical.

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30 Free Circuit Simulators Lightly Reviewed

We live in a time where great software is available with the click of a mouse, often for free or — at least — low cost. But there’s a problem: how do you select from so many alternatives? We were interested in [Lee Teschler]’s review earlier this year of 30 free circuit simulators. If you are selecting one or don’t like the one you are currently using, it is well worth the time to review.

There are several on the list that you’ve probably heard of before like GNUCap and LTspice. There are also some lesser-known products. Some of those are just trial or student versions of paid products. Some are branded versions of commercial products (like Tina) or were made free after selling for higher price tags (like MicroCap 12).

Old favorites like Falstad (which is apparently known as Circuit Sims) and TinkerCAD made the list. Many of the trial versions were very limited. For example, DCAClab only provides an NPN bipolar transistor model. Proteus doesn’t let you save or print unless you pay. While the list includes TI’s Tina, it doesn’t seem to mention that TI also provides a free version of PSpice which is a very popular professional product.

While the capsule descriptions are nice, you may want to dig in a little on the ones you are most interested in. For example, Falstad has a great mixed mode that can even include an AVR microprocessor. But there were a few on the list we had not heard of and maybe you’ll find something new there, too.

It’s A Bird! It’s A Plane! It’s… A Live Air Traffic Plane Spotting Simulation

Plane spotting has been a hobby of aviation enthusiasts for generations. Hanging out by the airport, watching aircraft come and go, maybe even listening to Air Traffic Control on a scanner from your local Radio Shack. Yep- we’ve been there, and it can be a lot of fun! But how can those of us who don’t live near a major controlled airport keep up on the action? As demonstrated by the [Information Zulu] YouTube channel’s Live Stream, seen below the break, the action may be closer than you think!

Aircraft on approach to LAX- Virtually

By using publicly available information, software, and some ingenuity, [Information Zulu] has created a live simulation of Los Angeles International Airport (LAX) for your simulated plane spotting pleasure. Aircraft positional data is gained through an ADSB receiver and piped into a the flight simulator software with a Traffic Injection Addon, and the simulator itself is used to properly place aircraft, set the weather, and even the correct aircraft types and liveries. Setting off the illusion of a real plane spotting adventure is the live Air Traffic Control radio chatter!

We love the creativity that went into not just making all of the software available, but in combining it into a cohesive product that can be viewed 24/7 on YouTube that, if you squint just right, could be mistaken for a view of the real thing.

If you’re not familiar with ADSB and how it’s used to track aircraft in such a way that anybody can receive it with the right equipment, check out this beginner’s course on ADSB from a few years back!

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