MicroSynth, the business card-sized synthesizer

MicroSynth Mixes All-Analog Fun With A Little Business

While [MicroKits]’ MicroSynth is an all-analog synthesizer that fits on a business card-sized PCB, and he actually does use it to break the ice in business meetings, that’s not really the idea behind this project. Rather, [MicroKits] is keen to get people playing with synths, and what better way than a synth you can build yourself?

There was an ulterior motive behind this project, too: prototyping circuits for a more complete synthesizer. Thus, the design is purposely very simple — no microcontrollers, no logic chips, and not even a 555 to be found. It doesn’t even have buttons; instead, the one-octave keyboard just has interdigitated traces that are bridged by the player’s fingers, forming resistive touchpads. The keyboard interface circuit is clever, too — [MicroKits] uses a pair of op-amps to convert the linear change in resistance across the keyboard to a nearly exponential voltage to drive the synth’s voltage-controlled oscillator (VCO). The video below shows what it can do.

We love projects like these because they show what can be accomplished strictly using analog circuits. We don’t have any problem with other synth designs, mind you — this 555-based dub siren we featured recently was great, too. Continue reading “MicroSynth Mixes All-Analog Fun With A Little Business”

Phasors In LTSpice

[Ted] recently demonstrated the analysis of an RL circuit using a piece of paper, Octave, and LTSpice. If you prefer, the Octave code should work fine in MATLAB, as well. If you are looking to get serious about electronic theory this is a reasonably simple case and is a good chance to get a workout with some of the tools.

We like the approach because too often it is easy to just use the computer and not pick up the understanding that you get when working through a problem by hand. You do need to understand complex numbers, but, overall, the math isn’t too hairy.

Continue reading “Phasors In LTSpice”

Tutorial On Signal Processing In Linux With Octave

If you’ve taken any digital signal processing classes at a college or university, you’ve probably been exposed to MATLAB. However, if you want to do your own work, you might think about Linux and one of the many scientific computing applications available for it.

[David Duarte] recently published a three-part tutorial on using Octave to do scientific audio processing. The first part covers basic reading, writing, and playing of audio files. Part two covers synthesis of signals, plotting, and some basic transformations.  Modulation is the topic of the third part. If you prefer your tutorials on video, you can check out the video below.

We’ve talked about MATLAB before in the context of message cracking. Then again, some of the best signal processing is done by humans. If you don’t like Octave, you might try Scilab, another Linux package that is similar. There’s also Freemat, Sage, and Spyder. Of course, you can also run MATLAB under Linux.

Analog Test Interface For Your Computer

Wanting to test the response curves on some analog parts, [Don Sauer] devised a way of using simple tools to graph analog tests on a computer. Here you can see the results of testing NPN, PNP, NMOS and PMOS transistors, but modifying the input circuitry would let you test just about anything you want.

[Don] is using an Arduino as the hardware interface. He needed some additional parts, like an op-amp and some passives. Instead of building this on a breadboard, he printed the circuit out on a piece of cardboard, hot glued the components in place, then wired them up. This will let him reuse the interface in the future, but is quicker than designing and etching a PCB.

He uses a Processing sketch to capture the test data streaming in from the Arduino. Once recorded, he uses SciLab to create the graphs. He also covers a method of sifting through the data using Octave, another open source program that feels somewhat like MATLAB.