Page 127 - 15 Dangerously Mad Projects for the Evil Genius

106 15 Dangerously Mad Projects for the Evil Genius

and 7 is a three-bit number (three binary digits). arrive at the motor. You could imagine this as a
Each of these digits can be 1 or 0, which is on or child sitting on a swing. If you just give the child
off. So a number 7 in decimal is actually 111 in short pushes, they will not swing as high as if you
binary, which means that all three colors would be give the child a longer push.
on, making the LED appear white. In a motor, the motor either receives full power
The expression: or no power, in pulses that arrive at perhaps a
thousand times per second. The motor has no time
!(color & 2)
to fully stop when the power is off, so the overall
effect is that the speed of the motor is controlled
will evaluate to 0 if the second bit of the color
smoothly.
number is set (green), and 2 if it is not. This may
seem the wrong way around, but the LEDs are
common anode, which means they turn on when
Summary
the output pins are at 0V rather than at 5V.
The allOff function simply iterates over every This project could be scaled up to use a bigger
LED pin, setting it to 5V. number of LEDs, although you would probably
have to use the Arduino’s bigger brother, the
Arduino Mega, as this has a lot more input/output
Motor Controller
pins on it.
PWM stands for pulse width modulation, and
If you search the Internet for “persistence of
refers to the means of controlling the amount of vision,” you will find many interesting ideas.
power delivered to a motor in this case. We use a People have even displayed video using this
simple PWM controller built using a 555 timer IC. approach.
We will meet the 555 timer again in Chapter 12.
In the next chapter, we switch our attention to
PWM controls the power to a motor by spying.
lengthening or shortening pulses of power that