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a digital & analog audio electronics blog by Michael Wiebusch

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Full Duplex over Coax – a Budget Cable Modem for your Arduino
May 13, 2026 · original
Update: Meanwhile the video of the talk at Hackaday Europe is online: And there is an article on Hackaday.com https://hackaday.com/2026/07/16/hackaday-europe-2026-build-a-cable-modem-for-your-arduino/ Documentation for the project shown at Hackaday Europe 2026 in Lecco. Link to paper pre-print: https://arxiv.org/abs/2603.18848 Find the KiCAD project for both 50 Ohms and 75 Ohms versions here (including board assembly plan): https://github.com/acidbourbon/TwoWayBox IMPORTANT: R10 is only an optional termination resistor for the TTL signal input. LEAVE THIS RESISTOR OUT if you directly drive the TTL input with an Arduino or Raspberry Pi or something similar that is connected with short leads! It’s just an option to terminate long signal cables coming from bench-top signal generators or something like that which has the power to drive LVTTL level into 50 Ohms.
Using Texas Instruments OpAmps in LTspice
Apr 30, 2026 · original
This is a quick guide to gaining access to a large variety of TI parts – in particular operational amplifiers – in LTspice. We’re going to export the SPICE macro directly out of TI’s own SPICE tool “TINA” and import it to LTspice. This is non-intuitive, but once you’ve seen how it’s done it’s not so hard. Both TINA TI and at least v17 of LTspice can be installed and run on Linux via WINE (just sayin). Remember: THE SPICE MUST FLOW, in our case from TI to LT. Step 1: Mining the SPICE Option A: GUI I assume you already have TINA ( https://www.ti.com/tool/TINA-TI ) installed. Open TINA and click on the register card “Spice Macros” then click on the OpAmp symbol on the left in the row just above. Then select your desired part and place it on the empty sheet. Right-click on the part and go to “enter macro” A text editor will open, showing you the entire .SUBCKT definition of the OpAmp. Select
IKEA cordless drill battery powering guitar pedalboard
May 5, 2025 · original
Motivation Guitar effect pedalboards … If this post is for you, I guess I don’t have to explain this concept in great detail here. Most of us have a USB power bank lying around somewhere that can charge your phone or wireless headphones, should you end up somewhere without access to a wall outlet. So you have a collection of your favorite guitar, bass or keyboard effect pedals, arranged nicely in a case – wouldn’t it be nice if you had something like a USB power bank to power your pedalboard on the fly, or at at a gig without needing to find a suitable outlet at the messy front of the stage? Yeah? Read on Complications In principle a beefy regular power bank can deliver enough juice to keep your pedals running for a while. And I tried it out with mediocre success. Here’s why: Power banks turn themselves off when you don’t draw a certain amount of current. If you only power a few analog p
A Maker Friendly Constant Fraction Discriminator
Jan 21, 2025 · original
TLDR I built a relatively simple, cheap, and most of all maker friendly Constant Fraction Discriminator for high precision photomultiplier (and SiPM) timing applications. I wrote a paper about the circuit, it was published open access (yay!), and now I hope you’ll read it Motivation When working with scintillation detectors and photomultiplier tubes (PMT) an often encountered problem is the so-called time-walk effect. This describes the phenomenon, that when evaluated with a comparator (or *discriminator*, as physicists like to call it), pulses of larger amplitude appear to arrive earlier than smaller pulses, because they surpass the comparator/discriminator threshold faster. (Image taken from my PhD thesis: http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/50844 ) So even though your Scintillator and PMT might have an intrinsic timing precision of some 100 ps or less,
YosysHQ FPGA toolchain with VHDL support
Dec 2, 2024 · original
TLDR I discovered that YosysHQ’s oss-cad-suite now “secretly” supports code entry not just in Verilog but also in VHDL. (Update: well I looked at older releases and VHDL support was there for a long time already – it just was not obvious to me! And I still see a lot of blog and forum posts claiming that you need the commercial version of oss-cad-suite for VHDL.) In this post I give a quick overview over the main components of the toolchain and show a quick and easy way to get an example VHDL project to compile. Motivation Over the past months I’ve become quite fond of the YosysHQ FPGA development toolchain . The best thing is: It’s completely open source! Of course not all FPGAs from all vendors are supported – but it’s great for makers to get started with some low-end low-price and low-power FPGAs like the Lattice iCE40 devices which were completely reverse engineered by project icestor
implementing a sigmoid function in analog circuitry
Feb 16, 2024 · original
Motivation This is a very short one – but I felt like sharing this with the world. I was playing around with the humble long-tailed pair transistor amplifier in LTSpice. I noticed something interesting – not only can it be used as a differential voltage amplifier, but it seems it can also be used to implement a sigmoid function. Wikipedia states : “A sigmoid function is any mathematical function whose graph has a characteristic S-shaped curve or sigmoid curve .” Famous sigmoid curves are the logistic function or the error function. Most anything that is an integral of some bell curve becomes a sigmoid curve. The circuit Nothing special, we only have two npn transistors and three resistors. The base of the right transistor is kept at 1V, while the entire circuit is powered with 3V. At the base of the left transistor we ramp up the voltage linearly, the output voltage is measured at the co
four buttons on one ADC pin
Jul 5, 2022 · original
Motivation Sometimes you just barely get away with the number of available microcontroller GPIO pins to implement the desired functionality — And then you discover that you have no more pins left to read out any buttons that a user could push to actually operate the device. What I present you now is a solution to get away with sacrificing just one µC pin and get four buttons in return without adding any additional digital (or analog) ICs. You might have guessed it, it can’t be just any GPIO pin but it has to be an ADC pin . With a tiny trick the circuit even allows to correctly decode combinations of two buttons pressed simultaneously. This technique is especially useful if you use an ATTiny85, i.e. you only have six GPIO pins to start with, but at least four of them can be used as ADC. Not The Circuit Okay, you say, that is simple – 4 buttons that is 4 bits of information = 16 different
a simple ringmodulator-ish FX pedal
Dec 21, 2021 · original
Demo Video Introduction Earlier this year I wrote a post about how to build a simple shortwave receiver with nothing but widely available hobbyist electronics parts, i.e. 74HCxx ICs, standard transistors and op-amps. Half-jokingly I called it “ a 74xx defined radio “. The heart of the receiver is a 74HC4051 analog switch that I use as a (slightly unorthodox but cheap and easy to use) HF mixer. Now I’m going to present you almost exactly the same circuit (or at least a part of it), working in the exact same way as in the radio, but instead of an antenna, we’re going to plug in an electric guitar. The goal is to make the guitar sound weird. Something like a ring modulator effect. The PCB you can see in the video was actually designed for the 74xx receiver but now has only half the components assembled :). Of course you can build the circuit just as well on normal protoboard. Schematic If y
Using CD4000_v.lib and 74hc.lib in LTSpice
Jun 30, 2021 · original
So, I was simulating a circuit in LTSpice and I wanted to use an 4000-series IC. Someone probably did that before, right? So I googled and found quite some posts mentioning the CD4000.lib or CD4000_v.lib library. But a lot of people are having quite some trouble using it. And soon I had the same issues and did not understand sh*t. So let me quickly guide you through the steps that made this damn library work for me (without me necessarily understanding everything that is going on). (The procedure is *exactly* the same for 74hc.lib , the only difference is to replace “VDD” with “VCC” everywhere.) Download CD4000_v.lib here and save it into your SPICE project folder as “CD4000_v.lib”. If you already have CD4000.lib (without the “_v”) then throw it away. Those two are different with respect to the VDD connection. Open LTSpice, click on File/Open and then open “CD4000_v.lib”. Choose “All Fil
yet another perpetual pendulum
Apr 17, 2021 · original
Introduction Heya. So I found people building perpetual self-exciting pendulums (pendula? pendulae?) and showing them off on youtube. Nice So far the most elegant that I know of seems to be THIS ONE by youtube channel [ TinselKoala ] … which is in turn a “cover version” of some original circuit by David Williams, published in the magazine(?) “Nuts & Volts” in August 2012. The circuit is shown at the very end of TK’s video . The basic idea is: You have a magnet on a string – the pendulum – which swings by a coil that acts both as a sensor (detecting the magnet is above) and an electromagnetic motor (giving the magnet a repulsive kick). Obviously the kicking has to occur at exactly the right time, i.e. when the magnet just barely swooshed past the center of the coil. Let’s be honest: The Williams/TinselKoala circuit is very close to perfection: Only two transistors and barely a handful of

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