1.b. Shield Features
|Wixel shield for Arduino top view.|
Wireless Sketch Uploading
The Wixel shield connections allow it to duplicate the functionality of the Arduino’s USB circuitry, which means the shield can wirelessly program the Arduino using the standard Arduino software. These connections do not interfere with the Arduino’s USB interface, so the Arduino’s traditional wired USB connection can still be used while the shield is connected. A schematic of the connections between the Arduino and the Wixel shield is available in Section 1.d. More information on wireless sketch uploading is available in Section 2.c.
General-Purpose Wireless Serial
The Wixel shield makes general-purpose wireless serial communication easy. Arduino serial functions, such as
Serial.print(), will transmit data wirelessly from the shield’s Wixel to a remote Wixel that then relays the information to the computer or embedded electronics to which it is connected. Similarly, data from the remote Wixel will be transmitted to the Wixel shield and can be read by Arduino functions like
Serial.read(). This enables wireless sketch debugging using the Arduino serial monitor, wireless communication between custom PC software and your Arduino, wireless communication between multiple Arduinos, and more.
The unused portions of the Wixel shield are configured as general-purpose prototyping space in which you can construct your own circuits. The holes in this prototyping area are connected in a breadboard-like configuration, as indicated by the top silkscreen. The traces connecting the prototyping holes are located on the bottom side of the shield and can be cut if a particular connection is not desired.
Arduino Reset Button, User LED, and Pins
Since the shield covers the Arduino’s reset button and user LED, the shield makes parallel versions of these components accessible on the shield itself. The shield features an Arduino reset button and a yellow LED (connected to Arduino pin 13). The shield pin spacing along the sides matches the standard (irregular) Arduino pin spacing, but these pins are additionally broken out to neighboring columns that are on a 0.1" grid. All square pads on the shield are ground.
The shield has four general-purpose 2/3 voltage dividers that can be accessed by the lower “HV” and “LV” pins (pictured above) located between the Wixel socket pins. These voltage dividers can be used to safely connect 5 V outputs to the Wixel’s 3.3 V inputs: connect the 5 V signal to one of the four HV pins and then connect the corresponding LV pin to the Wixel pin of your choosing. The voltage dividers are not connected to anything by default.
The shield has two general-purpose MOSFET circuits that can be accessed by the upper “HV” and “LV” pins (pictured above) located between the Wixel socket pins. These circuits can be used as inverters, level-shifters (e.g. to convert a 3.3 V Wixel output to a 5 V signal), or for driving larger loads (up to 200 mA) than you can with a Wixel or Arduino I/O pin alone (e.g. high-current LEDs or relays). The MOSFET circuits are not connected to anything by default. The circuit incorporates a BSS138 MOSFET (N-channel, 50 V, 200 mA, 1.5 V maximum gate threshold voltage).
The shield has space near the pin 13 LED that can be used for two general-purpose pushbuttons. The pushbutton pins are brought out to a series of through-hole pads that you can connect to other parts of your circuit. One easy way to add user-input pushbuttons to your Arduino is to jumper the upper pushbutton pin to the neighboring ground pad and connect the lower pushbutton pin to the Arduino or Wixel I/O line of your choosing (with that line’s internal pull-up enabled). In this configuration, the line is high by default, and it is driven low when the button is pressed.
The shield relies upon a pair of Wixels for its wireless connection. The shield’s Wixel socket allows the Wixel to be removed and used for other applications.
Note: The above features make the Wixel shield a good general-purpose prototyping board for Wixel projects. An Arduino is not required to use this board as a Wixel development platform.