The Apple II’s CPU clock has jitter or a glitch. This issue is not new—it has been present since its original design in 1977! Bald Engineer uses an oscilloscope to show how often the glitch occurs and how to correlate that jitter to its source—which is useful when you are not testing 40-year-old devices. The device under test (DUT) in this video is the Mega IIe project. It’s a fully compatible Apple IIe built around…

A long time ago, I made a video suggesting math was unnecessary to determine proper pull-up resistor values. Like most generalized statements, that suggestion is not always true. For example, in data buses like I2C, speeds like 400 kHz and 1 MHz are common. At those speeds, the pull-up resistor and the bus capacitance form an RC filter that fundamentally limits the data transmission speed. Or. It limits the range of pull-up resistor values. In…

Parker and Stephen invited me back to discuss the Mega IIe project on the MacroFab Circuit Break podcast. This discussion was far more casual than my past appearances. It was the first time I didn’t feel the need to do any prep work for their excellent questions! We talked through the overall experience of rev 1, rev 2, and rev 3. I appreciated the chance to talk about my motivations behind the Mega IIe project,…

KiCad 8 just dropped. Here’s an AddOhms video covering eight must-try features! The February 2024 release brings a whole host of new stuff to the Schematic editor. However, the PCB editor, CLI, and Simulation tools also received attention. (There are something like 900 closed issues for the 8.0.0 Milestone!) Which of these is your favorite? https://www.youtube.com/watch?v=Ohxlmy0p7FE In the video, I cover: Property Manager Panel (is now everywhere) A fix for Symbol pin or wire end…

USB-Based instruments that do not appear to the host as a virtual com port (VCP) usually use libusb for communication. The pyvisa-py driver for pyvisa can communicate with these instruments. However, you must first create a udev rule (and possibly a user group.) If you see the device in lsusb, but not the pyvisa ResourceManager, you need to add (or modify a udev rule): # backup 99-com.rules (if it exists) cp /etc/udev/rules.d/99-com.rules /etc/udev/rules.d/99-com.rules.BAK # (create…