Python is everywhere. Its capabilities continue to grow. Not only can you create simple scripts, but you can create full-blown applications with it. The core has been scaled down to run on 32-bit microcontrollers like the ESP32 and Adafruit Feather M0. You can even use Python engineer modules to design stuff like circuits. There are electronics Python modules that create schematics, simulate circuits, and make solving math a cinch. Here are some of the modules I found that make Python usable for (electronics) engineering.
Up front, make sure you have a functioning Python environment. Update the package manager “pip” since all of these electronics python modules rely on it. Speaking of dependences, you may need to also install third-party libraries for some of them. From what I can tell, these all should be platform independent. However, I only tested these electronic modules with 64-bit Windows.
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The most popular AddOhms video is my short tutorial on MOSFET basics. In the years since I posted the video, people have sent me many questions. While answering those questions I’ve learned quite a bit as well. For example, in that video, I say that Vgs is the threshold to turn on the MOSFET. Well, it turns out, that is not entirely true. It is the threshold to turn it off! Oops. Minor point with a subtle difference, but a common MOSFET misconception.
In this post, I dispel that and other common myths and misconceptions around using MOSFETs. As with all engineering tips and tricks, this post is not a definitive guide to FETs. Instead, it is meant to be a guide to help you ask the right questions to design in the correct part.
1. Misconception: You don’t need resistors on the gate
Back when I made the AddOhms episode, I added a resistor to the MOSFET’s gate pin. Of course any time a resistor is shown in a schematic, people get worried about what complicated formula is needed to determine its value. For slow switching applications, like below 10 kHz, the resistor value doesn’t matter. Something in the 100 to 1000 KOhm range is fine.
So if the value does not matter, why have one? The gate of a MOSFET is a small capacitor. And what happens when applying a voltage to a capacitor? It starts charging.
The initial current is very high. It slows down as the capacitor charges. That initial current rush, also known as in-rush current, can be a problem. Even though it is a short time, there is a significant current surge which can damage an I/O pin. Depending on the size of the MOSFET’s gate capacitance, it may not be necessary to include that resistor. I wish I could say to “just” add it any time you use a MOSFET. If there is a high switching frequency, say 100 kHz or higher, then you have to worry about the RC charging curve created by the resistor and the gate capacitance.
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Classic, vintage, or retro computer systems are well documented on sites like Wikipedia. Their historic position is well known. Their schematics are even published from original documentation. But how useful are those schematics in their current form? (Spoiler, not much.) Presented at KiCon 2019.
A common task for a transistor is switching a device on and off. There are two configurations for a transistor switch: low side and high side. The location of the transistor determines the type of circuit and its name. Either transistor configuration can use a BJT or MOSFET.
In this post, I draw the configuration for both transistor types, talk about which requires a driver, and explain why you would use either. If you are new to transistors, check out the resource links at the bottom. I have a couple of videos I made and some from element14’s The Learning Circuit which do a great job introducing transistors.
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On April 26th and 27th, the first year of KiCad KiCon kicks off in the Windy City. Join me and 26 others for talks about the open source electronics CAD tool. The list of speakers is impressive. There are many names which I follow on social media and some I recognize from the KiCad team. For example, Wayne Stambaugh is the KiCad project leader and has one of the keynote talks.
Bald Engineer’s Apple IIgs KiCon Talk
Here is the description for my KiCon talk.
While documentation exists for 1970’s and 1980’s calculators and computers, unfortunately they exist in bitmap formats. As I started converting parts of the Apple IIgs schematic to KiCad, I realized something. There are benefits to “preserving” historical schematics in a living, active, and open format. In this talk, I talk about my experiences in converting scanned PDFs into KiCad, the project behind that motivation, and to encourage help from others to preserve history with KiCad.
So what is it? Well, several months ago, I did a couple of Apple IIgs hardware live streams. I have a project in mind for the MEGA-II ASIC. But before I could move forward on the project, I wanted a modern version of the IIgs schematic.
While schematics for classic 8 (and 16-bit) computers are readily available, they are usually only in PDF format. Studying the design is like reading a book. While I am glad the PDFs are available, I would like to be able to do actions like a search.
In my talk, I’ll explain why we should be converting these classic schematics into an open format. Along the way, I’ll take the audience through my journey of using KiCad for this project. In the end, I’ll be asking for help to convert other classic computer schematics.
Where is KiCad KiCon 2019?
The location for the conference is mHUB in Chicago, IL. If you’re able to attend in person, I look forward to meeting you. If you’re not able to travel, I fully expect either a live stream or recorded versions of the talks to be available.