Motor with Potentiometer as Input
For this part of the lab, we use a potentiometer (analog input) to control the motor. The input is fed into Arduino where it is then converted to a digital signal and sent out to the base of the transistor. This signal controls the amount of power that flows from the collector to the emitter. When we increase the power sent to the base of the transistor, the current from the base to emitter increases, which causes the motor to spin faster. 

Motor controlled by potentiometer

So How Does a Transistor Work Exactly?!
"The design of a transistor allows it to function as an amplifier or a switch. This is accomplished by using a small amount of electricity to control a gate on a much larger supply of electricity, much like turning a valve to control a supply of water." - Physlink.com

Sticking to the water valve analogy, increasing the voltage at the base (but still less than the collector) is equivalent to opening the valve to let water through. When we increase the voltage at the base, we increase the current that runs through the transistor from collector to emitter. This is a result of the base being more positive than the emitter. When we increase the 'positive-ness' of the base, we pull more electrons from the emitter. Since we know that current moves in the opposite direction of electrons, we can assume that the current is moving from collector to emitter.

Motor Operated with an H-Bridge
The H-bridge is used to reverse the polarity of a motor. Wikipedia has a very good and short writeup on how it works exactly.

Motor rotation in both directions with an H-Gate

Motor Munny
For the last part of the lab, a motor was installed into a Munny doll. Clay was placed into the cavity of the body to physically secure the motor. The head was then mounted onto the motor and then connected to the first circuit setup with the potentiometer. Here's Munny spinning it's head. Enjoy!

Installing a motor into mini Munny

More Information

• Decoupling Capacitor via Wikipedia
• How does a transistor work? 
• H-Bridge via Wikipedia

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Copyright (C) 2007 Alain Georgette / Copyright (C) 2006 Frantisek Hliva. All rights reserved.