Hardware Reference
In-Depth Information
In Figure
1-1
you can see a simple bracket holding a small push button (top right).
This has been wired up to P6 for a reset button. This is not strictly required if your power
supply is working correctly (power-on reset works rather well). Unlike an AVR setup,
you
are not likely to use reset very often
. Chapter 3 of
Raspberry Pi Hardware Reference
(Apress,
2014) has more details about this.
The LED was added to the station last. It was soldered to a pair of half-inch finishing
nails, nailed into the wood. The LED's cathode has a 220 W resister soldered in series with
it to limit the current and wired to ground. The anode is connected to the Fahnestock clip
labeled LED. The LED can be tested by connecting an alligator lead from the LED clip to
the +3.3 V supply clip (this LED also tolerates +5 V). Be sure to choose a low- to medium-
current LED that requires about 10 mA or less (16 mA is the maximum source current
from a GPIO pin).
To test your prototyping station, you may want to use the script listed in the “GPIO
Tester” section in Chapter 10 of
Raspberry Pi Hardware Reference
(Apress, 2014). That
script can be used to blink a given GPIO pin on and off in 1-second intervals.
Adafruit Pi Cobbler
A much easier approach to prototype connections for GPIO is to simply purchase the
Adafruit Pi Cobbler kit, which is available from the following site:
This kit provides you with these features:
•
Header connector for the Pi's P1
•
Ribbon cable
•
Small breakout PCB
•
Breakout header pins
After assembly, you plug the ribbon cable onto the header P1. At the other end
of the ribbon cable is a small PCB that provides 26 pins that plug into your prototype
breadboard. A small amount of assembly is required.
Gertboard
Students might consider using a Gertboard, which is available from this site:
The main reason behind this recommendation is that the Raspberry Pi's connections
to the outside world are sensitive, 3.3 V, and vulnerable to static electricity. Students
will want to connect all manner of buttons, switches, motors, and relays. Many of these
interfaces require additional buffers and drivers, which is what the Gertboard is there for.
