Creating Custom KiCad Schematic Symbol in 5 Steps

Quickly make a KiCad Part

KiCad Schematic Symbol

A new project I have started working on involves the Apple IIgs. It was Apple’s last 16-bit (and 8-bit) computer. Inside are many application specific integrated circuits, or ASICs, that make the IIgs an extraordinary member of the Apple II family. One chip, in particular, is called the “MEGA-II.” This chip takes all of the individual logic chips from the original Apple II design and incorporates them into a single 84-pin PLCC.

The project I have in mind needs the MEGA-II. I need to design some printed circuit boards for it and a few other IIgs chips. That goal means I need at least one custom Kicad schematic symbol. I plan to create a custom library of Apple IIgs components.

Like other computers from the same era, complete schematics are available. However, they are not in a modern format. Since I need to create symbols for so many of the chips as it is, I may end up re-creating the entire IIgs schematic.

For now, here is the process I use to create custom KiCad schematic symbols and parts.

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Looking through my parts boxes, I have counted at least 15 distinct “Arduino boards” in my collection. Either they are variants of the Uno form factor or they have different processors from the 8-bit boards. That number easily goes to 30 if I include boards with just the “Arduino header” on them. This pile of microcontrollers got me thinking, how does anyone ever choose the right board?

For example, I have had several people tell me the ESP32 is the “ultimate Arduino.” But is it? Well, yes and no. Extra hardware you do not need can lead to complexity and unexpected behavior. When using an advanced module like the ESP32, it is important to learn how to use sleep modes to limit current consumption, especially for battery applications. But if you need WiFi, Bluetooth, I2C, SPI, UART, and high-performance processing, capacitive touch, GPIO, and analog inputs then the ESP32 is an obvious choice.

As for the other boards, I have written a guide to picking the right Arduino. You can find it over on the Hackster.io blog.

Read: Picking an Arduino

Appearance:How to pick from all the Arduino boards
Outlet:Hackster.io Blog
Format:Magazine

Arduino millis() plus addition does not add up

Here's why you should use subtraction with millis()

Arduino millis banner

In the past, I’ve covered how to reset Arduino millis() and have provided a growing list of examples using millis(). While reviewing the code for the elegoo Penguin Bot, I was reminded of a millis() mistake I see often: addition. The only way to properly handle millis() rollover is with subtraction. Let’s look at why (and how.)

What is Arduino millis()

The Arduino library has a function called millis() which returns the number of milliseconds the processor has been running. On other platforms, you might see references to a “tick counter.” It is the same idea. A hardware timer keeps incrementing a counter at a known rate. In this case, that rate is milliseconds.

A mistake new programmers often make is trying to “reset millis().” A better method is to compare two time-stamps based on millis(). So this if-statement is comparing a previous timestamp to the current value of millis().

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Penguin Bot from elegoo hands-on review of the kit build

Reviewing a dancing robot

Penguin Bot Black Red and Clear

Recently I received three packages from Elegoo Industries. They are a company based in Shenzhen China. Before those packages, I noticed there name several times on various electronics kits on Amazon. They asked me if I’d help them with a video that shows how to assemble their latest creation: Penguin Bot.

There is not much point in sharing that video with you unless you’ve purchased one. So instead, here is my review, or hands-on, of the kit. I will, however, show you a short Instagram video I made to show off Penguin Bot’s cuteness

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Arduino MKR Vidor 4000 Hands-On

Is the Arduino FPGA worth buying?

Arduino MKR Vidor 4000 - Blue

Earlier this week, I looked at the Arduino MKR Vidor 4000 during an AddOhms live stream. My goal was to understand the Vidor better. It is the new FPGA-based Arduino which started shipping this month. It runs about $60. You can learn more at the Vidor Product Page on the Arduino website.

In this post, I briefly touch on the difference between an FPGA and a microcontroller. Then I walk you around the MKR Vidor 4000’s board. Using one of the examples, I talk a bit about how the various chips communicate with each other. This section also highlights what makes the Arduino FPGA board different from other development boards. Lastly, I answer “should you buy an Arduino MKR Vidor 4000?”

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This AddOhms episode is part 3 of the “design your own Arduino” series. In this one I populate a bare PCB, reflow solder it, debug a few issues, and load the Uno bootloader. Originally, I designed 2 versions of the board. One version contained an error that I planned to fix in the episode. Well, turns out, the “correct” board had two issues which were more interesting.

Check out the #27 show notes for links to a bunch of stuff in the episode, including the design files.

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Five Arduino math fixes for when it is wrong

Check these when your Arduino can’t math

Arduino Math

While the Arduino library does an excellent job of hiding some of C/C++’s warts, at the end of the day, it is still just C/C++. This fact causes a few non-intuitive issues for inexperienced programmers. When it looks like Arduino math is wrong, it is probably one of these reasons.

When people ask me for help with their programming, I check each of these Arduino math mistakes. If your code seems to be hitting a bug, check to make sure it is not how the compiler handles math.

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Arduino EEPROM stores any datatype

.get() and .put() make saving floats easy

Arduino EEPROM Hero 1600px

Funny how a simple idea can spider out into multiple paths. Arduino EEPROM seemed like a straightforward concept. A few a years ago it was as easy as having either 512 or 1024 bytes of flash memory. The Arduino IDE offered an EEPROM library which let you read and write a single byte. Today, however, with many different processor architectures saving data to EEPROM varies. It is now possible to save any datatype to EEPROM but not on all boards and not all using the same method.

While programming an coin accepter sold by Adafruit on an AddOhms live stream, I discovered two “new” methods in the Arduino library. At least, these functions are new to me! A couple of years ago EEPROM.get() and EEPROM.put() appeared. Using these functions, you can store any datatype in EEPROM.

This post covers tidgets related to using Arduino EEPROM to store any value across multiple boards, or platforms. Specifically boards such as the Uno, Nano, Mega, and Zero are covered. Additionally Arduino-compatible boards from Espressif, PRJC, and Adafruit are covered as well.

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Learn Six Oscilloscope Measurements with an Arduino DUT

Grab an Uno and learn how to use your scope!

Oscilloscope Measurements with RTM3004 Alternative

One of the best ways to learn how to use a new piece of test equipment is to use it. Sounds easy, right? The problem is, sometimes when you are in the middle of troubleshooting your circuit, figuring out what the knobs on your scope do is an immense frustration. Use these 6 oscilloscope measurements, and just an Arduino Uno, to learn how to use a new or unfamiliar digital scope.

This tutorial is not a step-by-step guide on how to make each of these measurements on a particular scope. Instead, it is a general explanation on how to setup the Arduino and a screenshot to help identify if you set up your scope correctly. I reference the R&S RTM3004. However, practically any two (or more) digital channel oscilloscope should work.

Between each measurement, I highly recommend using your scope’s default setup (or autoscale) before proceeding to the next one!

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5 LDO Regulator Considerations other than voltage and current

A lesson in reading the data sheet

Pryamiduino R4 with LDO Regulator Disabled

For an AddOhms series, I created a DIY Arduino I am calling the “Pyramiduino.” It is an ATmega328p based board in the shape of a triangle. Other than being cute, the shape does not offer any other benefit. The design features a 3.3 volt LDO Regulator, which is also the subject of this post.

I forgot a fundamental aspect of design: read the freaking datasheet. The board’s LDO regulator was not turning on. Adding a passive scope probe to the circuit suddenly fixed the problem. The regulator turned on. When touching the enable pin, it measured about 1.25 volts.  While I am sure Rohde & Schwarz would like me to ship scope probe with each board, that was not an option. With the impractical fix in place, I got to thinking about that voltage level. I remembered that the datasheet mentioned about 1.2 volts was needed for the “HIGH” threshold. Which meant, 1.25 volts applied to the pin enabled an active low input. Not only that, I remember the datasheet clearly said it had a pull-down resistor built-in. What was going on?

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