Page 205 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 6 Options for Creating and Controlling Motion 183

Using decoupling capacitors is a quick-and-dirty method to keep energy spikes in your
mechanism’s circuit under control, rather than using some of the ready-made smart
modules we talked about earlier that do this kind of thing for you. A 0.1 μF capacitor
generally works well for bridging the connections on a DC motor and smoothing
energy spikes.

Separating Logic and Motor Power Supplies
It’s a good idea to separate the power supplies for your motor and the logic—the
breadboard circuit or Arduino—that is controlling it. There are a few good reasons
for this:

• Most controllers (like the Arduino) and chips (like the 555 timer and H-bridge)
take power at 5V. Your motor will most likely want something different. If you
try to power your 5V Arduino and your 12V motor from the same battery
pack, one of those paths is going to waste a lot of energy or not work at all.
Isolating the power supplies means you can choose the right supply for
each job.

• If your motor needs more current and voltage than you can safely run through
an Arduino (anything over 500mA), you absolutely need a separate power
supply.
• Even if your circuit or Arduino can supply the voltage and current your small
motor needs, you will still see noise in the system from turning motors on and
off and switching directions. Diodes and decoupling capacitors can help this
situation, but it’s still a good idea to keep the power supplies separate and
avoid the problem altogether.

NOTE Even if you separate the power supplies for your controller and
motor, you must connect the ground wires together. It’s good practice to
keep the circuit and the power supply grounds at the same low energy level
in order for the logic to talk to the motor effectively.

Relays and Transistors
Transistors and relays are like electronic switches. Mechanical switches are switched on
and off with your finger. Transistors and relays are switched by an electrical signal. You
need them when working with motors, because most of the time, the amount of