Robot Building for Beginners, Third Edition

CHAPTER 27 ■ ENCORE

Selection Criteria

When selecting a voltage regulator, look for your desired final output voltage, the minimum input voltage,
the maximum input voltage, the maximum current allowed, and the typical quiescent current (how much
current the regulator uses for itself ).
Other beneficial features to look for in a voltage regulator include reversed battery protection, thermal
shutdown if overheating, and damage protection if the attached board has a short circuit.

Capacitors

As described earlier, capacitors are power storage devices. Unlike batteries, capacitors don’t hold a lot of
energy, but they can charge and discharge an almost unlimited number of times. Most capacitors are small,
lightweight, and inexpensive.
Almost every robot circuit requires capacitors. The line-following circuit is fairly rudimentary, but
probably would require a couple of capacitors if additional chips were added.

Capacitor Roles

Capacitors have a number of vital uses:

• Absorbing small power spikes and power dips (reducing electrical noise); often
  called a “decoupling” capacitor in this role


• Providing large bursts of power on demand, such as when a motor starts up


• Maintaining circuit power to a memory module or real-time clock for a short time
  while a battery is being replaced


• Storing regulated voltage


• Acting as buckets to increase voltage in a voltage multiplier circuit


• Creating an inexpensive oscillator or timer by charging and discharging slowly across
  a resistor; often called a “timing” capacitor in this role

Capacitor Characteristics

The two most important characteristics of a capacitor are the maximum amount of charge it can hold
(expressed in farads, abbreviated F), and the maximum voltage it can handle (expressed in volts, abbreviated V).
The maximum voltage is easy to understand; don’t use a 6.3 V capacitor to store 9 V.
The amount of charge, F, is a little more difficult to comprehend, but it will be clearer once you see how
it is commonly used and its capacitor ratings:

• Greater than 10000 mF: used for industrial and military machinery, and solar panel
  collection. Smaller voltages are used to retain memory or system clocks.


• 100 mF to 10000 mF: used to provide large bursts of power for motors or other current-
  hungry components. Upper values used on solar robots.


• 1 mF to 100 mF: retains a short-term supply of power from a voltage regulator or
  power supply.


• 0.1 mF: used to connect to the positive and negative pins of chips to reduce electrical
  noise.