Pololu Wixel User Manual download pdf (Page 51)

A Wixel controlling a chain of ShiftBrites.

• invert_x: Set to 1 to invert the horizontal movement of the mouse. Default is 0.

• invert_y: Set to 1 to invert the vertical movement of the mouse. Default is 0.

• speed: A positive number that determines the speed of the mouse. Default is 100. This speed is linearly

proportional to this number.

Alternative Parts

You could replace the battery pack with a single 9 V battery and a step-down regulator that outputs voltage within

the Wixel’s 2.7–6.5 V operating range, such as our step-down voltage regulator D24V3ALV [http://www.pololu.com/

catalog/product/2101], or you could use a 1- or 2-cell holder along with an appropriate step-up voltage regulator, such as

our 5V boost regulator NCP1402 [http://www.pololu.com/catalog/product/798].

You could replace the accelerometer by any other accelerometer [http://www.pololu.com/catalog/category/80] whose

outputs are equal to one half of the input voltage when the acceleration on the corresponding axis is 0.

Mouse Speed Calculation

The mouse speed is calculated from the measured acceleration vector of the device. The acceleration vector normally

points straight upwards and has a magnitude of 1 g due to the Earth’s gravity. The Wixel measures the X and Y

outputs from the accelerometer, which tell it the components of the device’s acceleration vector in the plane of

the accelerometer. The resulting two-dimensional vector is then multiplied by its own magnitude to achieve greater

control at lower speeds. The vector is then multiplied by the speed parameter to convert it into a mouse speed which

is reported wirelessly to the computer.

9.i. ShiftBrite App

Overview

This app allows you to wirelessly control a chain of one or more

ShiftBrite [http://www.pololu.com/product/1222] RGB LED modules at a

distance of 50 feet or more from a PC. You will need two Wixels to

set up the wireless link: one connected to the ShiftBrites, running

the ShiftBrite app, and one connected to your PC with USB, running

the Wireless Serial App (Section 9.b). Using a terminal or your own

software, you can send a series of hex characters indicating the

desired color for each module to the virtual COM port. The

characters are transmitted wirelessly, received by the remote Wixel,

decoded, and sent to the ShiftBrite chain, causing each module to

light up with the specified color. Approximately 1000 color

commands can be sent per second, allowing large displays or

smooth animations.

The ShiftBrite App is also compatible with the ShiftBar [http://www.pololu.com/product/1242], which uses the same

control electronics.

Installation Instructions

Follow the instructions for the Wireless Serial App in Section 9.b to set up and test a basic wireless serial

link between two Wixels, using the latest version of the Wireless Serial App. Download the ShiftBrite App

(v1.1) [http://www.pololu.com/file/download/shiftbrite-v1.1.wxl?file_id=0J469] (20k wxl). Open it with the Wixel Configuration

Utility, choose your settings, and write it to one of the Wixels. See Section 4 for more information on how this is

done.

9. Wixel Apps Page 51 of 64

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