Pololu Wixel - Manual (Page 45)

After you have loaded this app onto a Wixel, the Wixel will appear to the computer as Virtual COM Port (with USB
product ID 0x2200). If you are using Windows, you should see an entry labeled “Wixel” in your Device Manager in
the “Ports (COM & LPT)” category while this app is running. You can not send or receive data on this COM port. Its
only purpose is to let the Wixel Configuration Utility easily get the Wixel into bootloader mode.
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.
• Pm_n_link: The link ID of pin Pm_n where m is the port number (0–2) and n is the pin number (0–7).
Default Settings
The default settings are:
Pin Link ID Function
P0_0 -1 Input with pull-up resistor.
P2_1 (red LED pin) 1 Output linked to P0_0 on the other Wixel.
Therefore, if you load this app onto two Wixels using the default settings, they should behave as follows: If nothing
is connected to either Wixel’s P0_0 line, the red LEDs on both Wixels will be on. If you connect the P0_0 line of one
Wixel to GND using a wire, then you should see the red LED on the other Wixel turn off. This demonstrates the basic
operation of the app.
Example Uses
• A Wixel output pin can be used to control an LED. Be sure to use an appropriate current-limiting resistor in
series with the LED (e.g. 1 kΩ)
• A Wixel input pin can be used to read the state of a button or switch. Connect the button or switch between
the input pin and GND, so that when the switch is open the pin will read high, and when the switch is closed the
pin will read low.
• A Wixel output pin can be connected to an input pin on another microcontroller.
• A Wixel input pin can be connected to an output pin on another microcontroller. The output must not drive to
a voltage higher than 3.3 V. If your microcontroller is running at 5 V you could get around this by using a diode
or putting your output pin into open-collector mode (never drive high).
Caveats
• A change on an input pin will usually be reflected on the corresponding output pin(s) within 10–100 ms,
but every radio packet has a chance of being lost so there is no guaranteed latency. Therefore, this app is only
suitable for very low-speed digital signals such as the signal from a pushbutton or the signal used to control an
LED. This app is not suitable for PWM or RC servo signals.
• This app uses digital I/O which means that every reading is transmitted as a 0 or 1. This app does not support
analog voltages.
Pololu Wixel User's Guide © 2001–2014 Pololu Corporation
9. Wixel Apps Page 45 of 64