Arduino uno User Manual

After including all of the libraries we need, we define the NUNCHUK_DEVICE_ID
constant. I
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C is a master/slave protocol; in our case, the Arduino will be the
master, and the Nunchuk will be the slave. The Nunchuk registers itself at
the data bus using a certain ID (0x52), so we can address it when we need
something.
In initialize , we establish the connection between the Arduino and the Nunchuk
by sending a handshake. In line 7, we call Wire ’s begin method, so the Arduino
joins the I
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C bus as a master. (If you pass begin an ID, it joins the bus as a
slave having this ID.) Then we’ll begin a new transmission to the device
identified by NUNCHUCK_DEVICE_ID : our Nunchuk.
We send two bytes (0x40 and 0x00) to the Nunchuk, and then we end the
transmission. This is the whole handshake procedure, and now we can ask
the Nunchuk for its current status by calling update . In the following figure,
we see the message flow between an Arduino and a Nunchuk.
Arduino Nunchuk
6 data bytes
Handshake (0x40, 0x00)
Request new data (0x00)
6 data bytes
}
repeat
update first pauses for a millisecond to let things settle. Then we request six
bytes from the Nunchuk, calling Wire.requestFrom . This doesn’t actually return
the bytes, but we have to read them in a loop and fill our buffer. Wire.available
returns the number of bytes available on the data bus, and Wire.read returns
the current byte. We cannot use the bytes we get from the Nunchuk directly,
because the controller obfuscates them. “Decrypting” them is easy, as you
can see in decode_byte .
Finally, we call request_data to tell the Nunchuk to prepare new data. It transmits
a single zero byte to the Nunchuk, which means “prepare the next six bytes.”
Before we actually use our Nunchuk class in the next section, take a look at the
documentation of the Wire library. In the Arduino IDE’s menu, choose Help
> Reference and click the Libraries link.
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Building a Nunchuk Class • 151
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Arduino uno Specifications

General

Form factor	Arduino
Certification	RoHS, FC, CE
Processor model	-
Processor frequency	- MHz
Microcontroller model	ATmega328
Microcontroller frequency	16 MHz
DC input voltage	7-12 V
Operating voltage	5 V
DC current per I/O pin	40 mA
Flash memory	0.032 MB
Maximum internal memory	- GB
SRAM (Static Random Access Memory)	2 KB
EEPROM (Electrically Erasable Programmable Read-Only Memory)	1 KB
Wi-Fi	No
Number of analog I/O pins	6
Number of digital I/O pins	14

Weight and Dimensions

Board dimensions	53.4 x 68.6 mm