Oscilloscopes are one of our favorite tools for electronics development. They make the hidden dances of electrons visually obvious to us, and give us a clear understanding of what’s actually going on in a circuit.
The question few of us ever ask is, how do they work? Most specifically—how do you design a circuit that’s intended to measure another circuit? Aleksa Bjelogrlic has pondered that very idea, and came down to explain it all to us at the 2023 Hackaday Supercon.
[Jean-Francois Debroux] spent 35 years designing analog ASICs. He’s started a book and while it isn’t finished — indeed he says it may never be — the 180 pages he posted on LinkedIn are a pretty good read.
The 46 sections are well organized, although some are placeholders. There are sections on design flow and the technical aspects of design. Examples range from a square root circuit to a sigma-delta modulator, although some of them are not complete yet. There are also sections on math, physics, common electronics, materials, and tools.
A chaotic drone of meaningless sound to lull the human brain out of its usual drive to latch on to patterns can at times be a welcome thing. A nonsense background din — like an old television tuned to a dead channel — can help drown out distractions and other invading sounds when earplugs aren’t enough. As [mitxela] explains, this can be done with an MP3 file of white noise, and that is a solution that works perfectly well for most practical purposes. However he found himself wanting a more refined hardware noise generator with analog controls to fine tune the output, and so the Rumbler was born.
It’s a tight fit, but it does fit.
The Rumbler isn’t just a white noise generator. White noise has a flat spectrum, but the noise from the Rumbler is closer to Red or Brownian Noise. The different colors of noise have specific definitions, but the Rumbler’s output is really just white noise that has been put through some low pass filters to create an output closer to a nice background rumble that sounds pleasant, whereas white noise is more like flat static.
Why bother with doing this? Mainly because building things is fun, but there is also the idea that this is better at blocking out nuisance sounds from neighboring human activities. By the time distant music (or television, or talking, or shouting) has trickled through walls and into one’s eardrums, the higher frequencies have been much more strongly attenuated than the lower frequencies. This is why one can easily hear the bass from a nearby party’s music, but the lyrics don’t survive the trip through walls and windows nearly as well. The noise from the Rumbler is simply a better fit to those more durable lower frequencies.
[Mitxela]’s writeup has quite a few useful tips on analog design and prototyping, so give it a read even if you’re not planning to make your own analog noise box. Want to hear the Rumbler for yourself? There’s an embedded audio sample near the bottom of the page, so go check it out.
Digital design is hard. But in the right environment, digital circuits are more forgiving than analog. That 3.3V signal coming out of the chip has to drop a lot along the way to not be a logic level at the destination. If you are trying to push the boundary then digital design has much of analog design, but mostly you get a bit of a pass on many things that plague analog designers. Berkeley’s AI research group has been experimenting with using deep learning to evolve analog IC design.
Analog ICs are plagued with noise sources and often don’t have the margins that digital circuit designers enjoy. According to the post by [Kourosh Hakhamaneshi], designers often build a few blocks and attempt to lay them out in a way that should work and meet other requirements. Then they employ simulation, make changes as required, and simulate again. Accurate simulations can be very time intensive. You can read the actual paper, too, should you want to dig into the details.
Everyone has a chip-of-shame: it’s the part that you know is suboptimal but you keep using it anyway because it just works well enough. Maybe it’s not what you would put into a design that you’re building more than a couple of, but for a quick and dirty lashup, it’s just the ticket. For Hackaday’s [Adam Fabio], that chip is the TIP120 transistor. Truth be told, we have more than one chip of shame, but for audio amplification purposes, it’s the LM386.
The LM386 is an old design, and requires a few supporting passive components to get its best performance, but it’s fundamentally solid. It’s not noise-free and doesn’t run on 3.3 V, but if you can fit a 9 V battery into your project and you need to push a moderate amount of sound out of a speaker, we’ll show you how to get the job done with an LM386.
