Periscope demo: Pros and Con

My experience using Periscope, while soldering a kit

Periscope demo with the EMSL Three-Fives Kit

After fighting bugs, bad connections, and burned out chips your project is working–or even done. The next step? Record a video, edit it, and upload it to YouTube.

Too many steps? Then maybe you just want to do a Periscope demo. Within seconds, you can be broadcasting your project to the world.

This past weekend I tried my first couple of scopes. The first Periscope “demo” was me soldering together a Three Fives from Evil Mad Scientist Labs. The others periscope demos were 3d printing related.

When it comes to a hardware project demo, I see some challenges. Check out these five things to watch out for and, if you’re interested, you can watch my soldering Periscope demo.

Circuit Trading Cards Review

Arachnid Labs makes learning circuit basics simple

circuit trading cards review

One of my early hobbies as a kid was collecting baseball cards. At every card show, I was on the lookout for the  1989 Ken Griffey Jr Rookie card, #1, from Topps. My collecting craze lasted until the baseball strike in 1994. Then I lost interest in professional baseball and its collectibles.

You’re asking, what does this have to do with electronics? Well, the Circuit Trading Cards from Arachnid Labs reminds me of the days I spent trading baseball cards. Instead of memorizing RBIs and Homerun counts, these circuit patterns trading cards teach you circuit basics.

The card stock used is of high quality, and each unique card has a durable feel. One side is the Arachnid Labs logo while the other is what I call the “information side.” The information side is one of three colors: Yellow (Analog), Blue (Digital), and Green (Power).

The latest AddOhms looks at why you need a pull-up resistor when using push-buttons. This video goes into what happens when you leave a pin floating, what a floating pin means, and how the pull-up actually works. You can get more information about the video on the AddOhms Episode page.

This is the 2nd time I’ve made a video on pull-ups. Despite being a single resistor, it can be a difficult topic for new hardware designers to understand. The pull-up video was the first video tutorial I ever made. In fact, the YouTube version uses YouTube’s “stabilization” algorithm, which gives the video a very warped feel.

AddOhms #15 shows improvements in skill over the past couple of years!

Question: What’s another topic that I need to cover in an AddOhms Tutorial? You can leave a comment by clicking here.

Microcontroller state machine with enum tutorial


Flag variables are great, and totally not evil, when you just have two states: ON or OFF. What about when you have multiple states? Is there an option better than creating multiple flag variables?

The C-language has a declaration type just for this purpose. It is called an enumeration, or enum.

Setting up a state machine with enum is a surprisingly simple. Arduino and embedded programmers should use them!

All you need to do is create descriptive tag names, and let the compiler assign them an integer value. Unlike a #define which is just a macro replacement, the compiler treats an enum as your personal variable type.

This behavior comes in handy when you’re creating states for a state machine. I show how to create a simple state machine with enum, to blink an LED with millis(), in this post.

Benchmarking Arduino’s digitalWrite() with a Logic Analyzer

Just how fast is digitalWrite()?

digitalWrite with Logic and Arduino Uno

Recently I picked up a device called Logic from Saleae. It’s a 4-channel USB-based logic analyzer. While learning how the simple, but effective, UI works I ran some timing benchmarks on my Arduino Uno. The subject? digitalWrite(). I wanted to know how fastdigitalWrite() could turn on two (or more) pins.

Almost all Arduino users start out with the simple “blink” sketch. Turn pin 13 ON, delay, turn it OFF, and delay again. The heart of this version of “Hello World!” is the digitalWrite() function. Many Arduino users never even think about all of the stuff this single function call hides.

In this post, let’s compare the speed of digitalWrite() to direct port manipulation, using a logic analyzer.

Found this one while going through some old files. One of my favorite volunteering activities is introducing kids to engineering. After judging a FIRST competition, I learned about Central Texas Discover Engineering. They had a program that gave me a chance to spend an entire day talking to middle school kids about engineering.

I started the class with a simple question: “What do engineers do? Surprisingly, most of the kids answered pretty well. Then I went through these slides to give them an idea of other types of engineers. Lastly, we did a fun “engineering” activity.

Flag variables are not evil (for Microcontrollers)

Non-embedded programs shield your ears: flag variables are good

Fun With Flag Variables

Getting programming questions answered on the internet can be problematic. Programmers love to have opinions, stick to those ideas, and express them to you even when their opinion has nothing to do with your question(s).

Not only am I going to explain how to use flag variables in your code, I am going to encourage their use—which most programmers avoid.

However, this advice comes with two caveats.

  1. This information only applies to limited resource environments like an Arduino, LaunchPad or PIC.
  2. Use flag variables very carefully when you do use them.

The following flag variable usage examples are Arduino-centric but apply to any microcontroller platform, including the Energia project for TI Launchpads.

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.

Which Arduino Starter Kit is the Best?

Need an electronics kit? Check out these 4 options.

Which Arduino Starter Kit is Best

The other day my friend called me up. He told me how much he missed building circuits and wanted to start again with the Arduino.

So he asked me “which Arduino starter kit is the best to buy?” At which point, I drew a long breath. Easy question, not always an easy answer.

Picking out an electronics kit depends on a number of factors. You should consider:

  1. Your budget
  2. What you already have
  3. What you want to do

#1 and #2 are probably pretty easy to figure out. For many beginners, it’s “not much” and “nothing.” When you don’t know #3, what you want to do, then it gets trickier. Coming back to my friend, what did I do? Well, I went out and bought each one of the kits in this post. I put myself in his shoes and maybe these are your shoes as well.

Assuming you have about $100 to spend, have no components on-hand now and just want to “get started” consider one of these 4 Arduino starter kits.