Raspberry Pi A, User Manual, Page: 241 / 314

C H A P T E R 1 4
T H E G P I O P O R T
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To assemble the circuit, you’ll need a breadboard, two jumper wires, an LED and an appropri-
ate current-limiting resistor (as described in the “Calculating Limiting Resistor Values” side-
bar). Although it’s possible to assemble the circuit without a breadboard by twisting wires
together, a breadboard is a sound investment and makes assembling and disassembling pro-
totype circuits straightforward.
Assuming the use of a breadboard, assemble the circuit in the following manner to match
Figure 14-3:
1. Insert the LED into the breadboard so that the long leg (the anode ) is in one row and
the shorter leg (the cathode ) is in another. If you put the LED’s legs into the same row,
it won’t work.
2. Insert one leg of the resistor into the same row as the LED’s shorter leg, and the other
resistor leg into an empty row. The direction in which the resistor’s legs are placed
doesn’t matter, as a resistor is a
non-polarised (direction-insensitive) device.
3. Using a jumper wire, connect Pin 11 of the Raspberry Pi’s GPIO port (or the corre-
sponding pin on an interface board connected to the GPIO port) to the same row as
the long leg of the LED.
4. Using another jumper wire, connect Pin 6 of the Raspberry Pi’s GPIO port (or the cor-
responding pin on an interface board connected to the GPIO port) to the row that
contains only one leg of the resistor and none of the LED’s legs.
WARNING
Be very careful when connecting wires to the Raspberry Pi’s GPIO port. As discussed earlier in
the chapter, you may do serious damage to the Pi if you connect the wrong pins.
At this point, nothing will happen. That’s perfectly normal: by default, the Raspberry Pi’s
GPIO pins are switched off. If you want to check your circuit immediately, move the wire
from Pin 11 to Pin 1 to make the LED light up. Be careful not to connect it to Pin 2, though:
a current-limiting resistor suitable for a 3.3 V power supply will be inadequate to protect the
LED when connected to 5 V. Remember to move the wire back to Pin 11 before continuing.
To make the LED do something useful, start a new Python project. As with the projects in
Chapter 12, “An Introduction to Python”, you can use a plain text editor or the IDLE soft-
ware included in the recommended Raspbian distribution for this project as well.
Before you can use the Raspberry Pi GPIO port from Python, you’ll need to import a library
into your Python project. Accordingly, start the file with the following line:
import RPi.GPIO as GPIO