the Arduino when it comes to I/O capabilities. The beautifully-engineered
Gertboard is a plug-in add-on that neatly overcomes this deficiency
by giving the Pi access to an ATMega328, but it's a very complex and
expensive solution. An alternative would be to interface an Arduino
running at 3.3 volts to the Pi, though this is easier said than done.
But, we won't let that stop us, will we?
of something similar to this project.
It's called an AlaMode, and it goes for something like $50.
Our version will cost about a third of that to build.
As a first step, we will build an Arduino plug-in board for the Pi.
It is customary to call Pi boards "plates," but indulge me and permit
me to name this particular board a hoody. Thank you.
We will be using generic stripboard to build our project. Small (3-3/4"
x 2-1/16") boards can be obtained on eBay for a bit over a dollar apiece.
It is also possible to use something like a Radio Shack 276-168 protoboard
($3.49). The main component, though, is an 3.3-volt Arduino Pro Mini.
This will permit connecting directly to the Raspberry Pi ports and other
3.3-volt devices without having to do level shifting.
directly to the GPIO pins. This is not a good idea. Use buffer chips,
such as the 74HC4050 hex buffer, between the devices and the GPIO.
This protects the Pi from overvoltages, current surges, and your mistakes.
Far better to blow out a fifty-cent buffer chip than a $35 Pi.
This particular project connects directly to the GPIO Rx and Tx pins.
However, we are connecting to a 3.3 volt device, which limits the risk.
Still, a buffer chip would not be a bad thing here.
This is a moderately complex project, and beginners need not apply.
It requires skill at soldering and in the use of hand tools. Experience
with a continuity tester and a steady hand with a knife blade are also
Ready? Well, then, let's get on with it!