Pololu Wixel User Manual download pdf (Page 52)

Connecting the Wixel to the ShiftBrite chain

The following connections should be made between the Wixel running the ShiftBrite App and the first ShiftBrite in

the chain:

Wixel ShiftBrite Function

P1_4 EI Enable

P1_5 CI Clock

P1_6 DI Data

P1_7 LI Latch

GND GND Ground

Additionally, the Wixel and ShiftBrites may share the same VIN as long as the voltage requirements for both modules

are satisfied. For initial testing, you may alternatively use VALT to power the ShiftBrites from USB (see Section 5.a).

Using the ShiftBrite App

After making the correct connections and applying power, open a terminal program and connect to the COM port

created by the Wixel running the Wireless Serial App. Type ffffff. As you type the characters, they will be echoed

back to your terminal. Press Enter, and the first ShiftBrite in your chain will light up in white. Then type ff0000 and

press Enter; now the first ShiftBrite should be red, and the second should be white (if present).

To shift out multiple color commands at once, for example when you want to set the colors of the entire chain, type a

series of single-color commands without pressing Enter, then press Enter once to apply them all.

Parameters

• radio_channel: The channel number is from 0 to 255 and determines which frequency to broadcast on. The

default is 128. Wixels must be on the same channel to communicate with each other. To avoid interference,

Wixels that aren’t supposed to talk to each other should be at least 2 channels away from each other. For example,

you could have one pair of Wixels on channel 128 and another pair on 130.

• input_bits: The number of bits per channel that you would like to use to send color information. The allowed

values are 1 to 16, and the default is 8, which corresponds to colors represented by 6-digit hex values. However,

the ShiftBrite supports 10 bits of resolution, so choose a value of 10 to make use of its full dynamic range. In this

case, you must send 9 digits to set a color. For example, 3ff3ff3ff is the brightest possible white and 001000000

is the dimmest possible red. Other values for this parameter might be useful in special situations (e.g. 4 bits of

resolution lets you specify a full color in three bytes, such as f00 for red, which allows for a higher update rate).

• echo_on: Set to 0 to disable echoing of every character sent. While echoes are useful for debugging, you

might want to disable them for the highest possible speed.

Data Format

The data consists of a series of red, green, and blue (RGB) values, as ASCII hex strings. Each value contains from 1

to 4 characters, depending on the value of input_bits, specifying a number from 0 to 2

input_bits

-1. When a complete

set of R, G, and B values has been received, the values are multiplied or divided by the appropriate factor to match

the 10-bit ShiftBrite data format and shifted out to the ShiftBrite chain. An Enter character (ASCII 10 or 13) causes

the Latch pin to be toggled, instantly setting each ShiftBrite to its new color.

9. Wixel Apps Page 52 of 64

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Pololu Wixel User Manual Page 52