Sunday, June 03, 2007

Voodoo Electronics

I'm interested in robotics, but building robots requires three things: mechanics, electronics and software. (I'm intentionally ignoring BEAM here -- I'm not interested in building software-free robots.) I know software, and I feel like I have an okay grasp of mechanical systems. I don't know enough about electronics, though.

My understanding of electronics is that there are basically three types of electronics:

  • AC electronics. Not especially relevant to building robots.
  • DC digital electronics. This part I feel like I pretty much understand. It's based on boolean logic, and so a lot of my software knowledge is applicable. The only extra bits are pretty simple:
    • you're dealing with high versus low rather than true/false, so you need to come up with a mapping convention for each circuit and stick with it.
    • many components (like ICs) also need power. Just get a power source that's the right voltage and enough current, and this should be okay.
    • there are a few different "families" of digital components. Stick with one for any one circuit.
  • DC analog electronics. This has two main parts. The first part is the "simple bits": things like Ohm's law which every single electronics tutorial feels the need to tell you about. The second part is what I've come to call "voodoo electronics" -- the parts that every electronics tutorial I've ever seen simply hand-waves away.

A recent example of "voodoo electronics" that I encountered was in the most recent issue of Make. This issue had a number of electronics tutorials. Some of these were very helpful, like Your Electronics Workbench. The article on the 555 timer chip, however, The Biggest Little Chip, suffered from the voodoo electronic problem. The article contained the following schematic:

Figure 2 from "The Biggest Little Chip"

It then went on to explain the purpose of each of the various components one by one. The explanations were a bit terse, but reasonable. Eventually, the entire circuit had been explained except for R3 and C2. Here's how the article explained their purpose:

R3 protects the LED from excessive current, while C2 protects the 555 timer from random noise.

"Excessive current"? "Random electronic noise"? How am I supposed to design my own circuits without understanding how to both predict when these problems will exist and how to devise a defense against them? So far I have yet to see a single electronics tutorial that explains these things.

I ran into the same thing when I found some schematics for a stepper motor controller on the web. All of the schematics made sense to me, except a mysterious zener diode which was there (according to the documentation) "to absorb reverse EMF". No more explanation was given.

Are there any electronics tutorials out there that actually explain how to predict when part of a circuit will be susceptible to "random electronic noise", "excessive current", or "reverse EMF" and how to build protection against them, or is my only hope to take a full-fledged course in electrical engineering?


After posting this I realized that I could just post a comment on Make's website. The author of the 555 article posted a very helpful response. Now I just need to figure out what that zener diode in that stepper motor controller was for.

posted Sunday, June 03, 2007 (8 comments)