DIY Arduino Schematic board and Checklist

Things to consider when designing a custom board, based on an Arduino

DIY Arduino Schematic Banner

One of the last significant steps in a project is designing the custom PCB. This stage means creating a DIY Arduino board that is custom to the application. Two examples of my past projects are BinBoo, a Binary Clock, and Open Vapors, my reflow oven controller.

While working on a project for a friend, I got to thinking; it would be nice to have a checklist for circuit elements to include on a DIY Arduino board. In the early days, I forgot to add a filter cap to AREF, for example.

These tips are based on an 8-bit AVR design, like the ATmega328p chip. You could apply these tips to other 8-bit AVRs. Until now, I have not designed a custom board around a 32-Bit/ARM board. Though at only $16, I would be tempted to just solder the Teensy module directly to my finished board.

Below is a written list of items for a DIY Arduino checklist. If you’d like to see me design this board in KiCad, check out this AddOhms Tutorial.

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Arduino Keyboard Matrix Code and Hardware Tutorial

Here's how a keyboard works

As a kid, I got the book “Upgrading and Repairing PCs.” (Now in its 22nd edition.) It was the first book to explain to me the PC architecture. I considered, how were there so few pins on an AT-style keyboard connector when there were 101 keys on the keyboard? That is when I first learned about the keyboard matrix.

Intel_P8049_AH_controller

Original image from Deskthority Wiki. (Edited image is shown.)

The keyboard matrix itself did not amaze me, but instead the idea there was an entirely separate 8-bit microcontroller inside of the keyboard. Early keyboards may have used the P8049AH, which, there is still some stock available to purchase. I was fascinated with the idea an entire computer was necessary to run the keyboard, to use my “real” computer. Why did it take something as complicated as a microcontroller?

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A couple of weeks ago I wrote about four current flow direction myths. As a follow up to that popular post, I decided to dedicate this month’s AddOhms electronics tutorial video to Current Flow. In episode #19, I tackle the question of which way does current flow.

You might have heard about “conventional flow” and “electron flow.” In conventional flow, we assume that current flows from the positive voltage towards the negative voltage. In digital, the “negative voltage” is usually called ground. However, that’s not how the electrons move nor is it how they carry the charge around a circuit path.

Electron flow is the description of how electrons carry a charge. Which is the negative voltage towards the positive? This confusion is a result of Ben Franklin mistakingly identifying how electrons moved so many years ago. Yet, we have kept the “positive” and “negative” labels as they are today.

The key though is that it doesn’t matter which method you use to analyze a circuit. Electrons move in a closed path. So whether they travel from positive to negative or from negative to positive, doesn’t matter!

AddOhms #19: Current Flow Direction

Check out the full AddOhms Electronics Video Tutorial on Which Way Does Current Flow on the AddOhms YouTube Channel.

Capacitor lifetime depends on the materials capacitor lifetime

Although not all applications are safety critical or mission critical, reliability is still a vital consideration for many electronic products. Making informed choices at the part selection stage can help ensure the product will perform correctly over its intended lifetime.

When choosing capacitors, properties such as volumetric efficiency, frequency stability, temperature rating or equivalent series resistance are often the primary factors that govern technology choice. In these cases, understanding factors affecting lifetime can help engineers make sure the product will deliver the required reliability.

On the other hand, a long operational life may be an essential requirement of the end product.

Continue Reading the full article, “Capacitor reliability can be improved with the right materials,” on Electronics Weekly.

Date:September 28, 2015
Appearance:Capacitor reliability can be improved with the right materials
Outlet:Electronics Weekly
Format:Magazine

P-Channel MOSFET Tutorial with only Positive Voltages

From the mailbag (or chat… bag?)

Positive Voltages with a P-Channel MOSFET Tutorial

On every page of my blog, you might notice a chat window. If I’m not busy, we can chat in real-time. If not, the messages come to me by email. Here’s one I got from Matt the other day:

Let’s talk a bit about how (and why) you would use a P-Channel MOSFET. Matt, and he’s not the only one, is probably asking this question based on the “myth” that P-Channel MOSFETs require “negative voltage” supplies.

Keep reading for a how to use only positive voltage in this p-channel MOSFET tutorial.

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How to find parts for your electronics projects and designs

These are the tools I use to find parts, do you?

how-to-find-parts tips

What part is the most important part in building a project? All of them! Okay, bad joke. Selecting the right parts or components for a design is an area where both new hobbyist and veteran engineers struggle. The wide variety of devices make it almost impossible to know if you are selecting the right one.

Looking at a curated List, using component search engines and browsing DIY shops are how I tend to find parts for my projects.

You might want to bookmark these some of these sites so you can use them next time you’re stuck on how to find parts for your project.

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What’s the difference between Series and Parallel Circuits?

Example of Circuit and Parallel Circuits

Tutorial on schematics basics

The funny thing about schematics is that they are much easier to draw than they are to read. There are many common circuits. When an experienced engineer looks at them, it’s like a second language. When someone less experienced looks at them, it looks like random lines and symbols thrown together at the last-minute. (Or maybe that’s just the schematics *I* draw.)

Other than reading Schematic Symbols themselves, one of the basic skill necessary to read a schematic is recognizing series and parallel circuits.

In short if the same current flows through all the parts, they are in series.  While if current has different paths, they are in parallel.  Keep reading to dive into this tutorial on how ohm’s law applies to series and parallel circuits.

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Awesome 3D Board (BRD) Viewer for EAGLE

Cytec
3D Render of MSO Demo Board

3D Render of MSO Demo Board

Earlier I posted a PCB Checklist of items to double-check when sending your board out to a fab. The Dangerous Prototypes blog pointed to a 3D EAGLE PCB tool from a Bulgarian-based developer called Cytec that takes an EAGLE BRD file and renders it in 3D for you.

The example board I have above is a render of my MSO Demo Board. And I have to be honest, it looks much like that one! (more…)

Never trust an autorouter

I am not a fan of relying on the Autorouter in EAGLE — or any PCB CAD software for that matter. When laying out a board, I’ll use the autorouter to get an idea if the part placement is going to work or not. In this case, I was reminded how much autorouters suck! Even after running for while, the autorouter could only route up 50% of the nets (signals).

Never Trust The Autorouter

As Chris Gammell‘s T-Shirt Says, Never Trust The Autorouter.

It only took me about 20 minutes to start over and finish the manual layout. I still want to clean it up a little, but over all, I beat the Autorouter.

What is the board anyway?

In January I visited Tokyo on my annual work trip. While there, I ran over to Akihabara to check out a used media store called Traders. The multi-level store (like all those in Tokyo) sold used video games and movies. Each floor featured different platforms. My favorite was the 2nd floor which was all retro 8, 16, and 32 bit systems. Piles of Famicoms (NES), Super Famicoms (SNES), Mega Drives (Genesis), and other systems were all around. In the middle of the floor were racks of cartridges.

While there I picked up a couple of Rockman (Mega Man) carts, Super Mario brothers, and even Adventure island.

A US-based NES can play Famicom games since the basic hardware is the same. However, the pin outs are slightly different. Also, US-based NES systems look for a lock-out ship (CIC) that Famicoms don’t have. Fortunately I ran across a project that uses the ATtiny (AVRCICZZ) to emulate the lockout chip. So armed with that and some pinouts, I’ve created an adapter.

Keep subscribed, after a few more touches, I’ll post the EAGLE files as an Open Source Hardware (OSH) project.

iCircuit’s circuit simulator goes from iOS to Desktop

When it comes to schematic capture and circuit simulation on a mobile device, iCircuit for iOS got it right from the start. iCloud integration, intuitive touch controls, and fast application performance. Now (or Finally?), my favorite mobile circuit simulator, iCircuit, is available for OS X.

iCircuit with 555 Timer

iCircuit is based on the Falstad Circuit Simulator, which sadly, is a Java-based web app. For years I’ve installed the App on my iPhone and iPad almost immediately after turning on iCloud [for Android users, that’s basically the first step of activating an iOS device].

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