Driving Simple Loads with Transistors, Relays, and DC Motors
Microcontrollers are great for many things where you need a little bit
of computer smarts in a physical system.
One thing they’re not suited for is driving big electrical loads. The
pins on the AVR are great for driving small things like our LEDs or
even a speaker (decoupled with a capacitor so that it doesn’t draw too
much current). But they just don’t put out enough juice to turn a
motor—at least not a motor big enough to do anything meaningful!
This is a problem, because everybody needs a robot or two, and robots
need motors. The AVR chips (especially the larger ones) make a great
small-robot brain. Sure, you can make it flash LEDs and sing through a
speaker, but without legs or wheels, your robot is more like a brain
in a jar. Your mechanized killer droid is not going to get very far
without the ability to turn a motor.
We made a start on this problem in Chapter 11, where you saw
how to control servo motors. Servos are designed especially to accept
logic-level signals so that the AVR doesn’t have to do any heavy
lifting. In this chapter, I’ll cover a number of circuits that you can
use to allow the AVR to run motors that don’t have internal
It’s very strange to ask an administrator, “How do you solve problems?” Anecdotal evidence suggests that the people who gravitate toward these positions don’t have to think too much about it. After all, there’s hardly a wide variety of IT-centric academic disciplines, and within these disciplines there aren’t many classes or research specialties that center on the process of fixing things. It seems much more likely, especially in industries where IT has not been fully professionalized, that IT staff are drawn to their positions because they are good at fixing things, especially under circumstances of limited knowledge. Because this is the audience I’d like to speak to, it would be presumptuous to suppose that I have all the answers. I’d like to propose instead some formalization to the process of technical analysis: frameworks in which administrators can examine and more efficiently use their preexisting methodologies. Hopefully this allows administrators to specifically hone their already keen abilities, instead of simply going forward based on their natural talent.
Christine Horner is a board-certified and nationally recognized surgeon, author, professional speaker, and relentless champion for women’s health. She spearheaded legislation in the 1990s that made it mandatory for insurance companies to pay for breast reconstruction following mastectomy. She is the author of Waking the Warrior Goddess: Dr. Christine Horner’s Program to Protect Against and Fight Breast Cancer, winner of the 2006 IPPY award for Best Book in Health, Medicine, and Nutrition. Website: www.drchristinehorner.com
As a plastic surgeon, I specialized in taking care of people seeking to be more youthful. I was able to transform their surface appearance, but did nothing to truly reverse or slow down their aging or to improve their health—I only created an illusion of that. When I was introduced to an ancient system of medicine from India, called ayurveda, and personally experienced its astounding detoxifying, rebalancing, and rejuvenating effects, my approach to and understanding of health, aging, and beauty radically changed. After only forty-eight hours at an ayurvedic clinic, doing a program called panchakarma that powerfully detoxifies and rebalances the body, I looked a decade younger and never felt better in my life. There in the mirror, my reflection revealed a markedly younger appearance and a profoundly healthy radiance, which could never be achieved with the knife, or with lasers or chemicals. It was something that could only emanate from a state of remarkable health. That’s what my patients were seeking, but with the tools I had as a plastic surgeon, I could never give them what they truly desired. Now I realized that the principles and techniques of ayurveda—a five-thousand-year-old system of medicine—held the secrets to the real fountain of youth.