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182 Making Things Move
The side of the LED over the shorter ground leg is usually flat, so you can still tell
which side is ground, even if you clip the legs shorter. Install the LED in the circuit so
that current flows through it from the long leg to the short leg.
LEDs don’t limit voltage on their own, so you need to put a resistor in series with your
LED before hooking it up to most power sources, or else you’ll fry it. For example, if
you’re using a 5V power supply, a 220KΩ resistor will work well with most LEDs. At
higher voltages, you’ll need proportionally higher resistors to protect your LED.
Decoupling Capacitors
You can use capacitors to your advantage in circuits with motors to smooth out the
energy spikes that happen when motors are turned on or change directions.
Capacitors used for this purpose are called decoupling capacitors.
A popular approach is to solder a capacitor across the two leads of a DC motor before
ever using it, just to be safe. You may also see capacitors soldered from the motor leads
to the motor housing (see Figure 6-40). Make sure to use ceramic (not electrolytic)
capacitors for these applications, since they don’t care which way the current flows
into them. This will allow you to run the motor clockwise or counterclockwise with
no worries.
FIGURE 6-40 Decoupling capacitors soldered to DC motor leads