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SNAPconnect E12 User Guide — 116-081614-030-B001
Extending the E12 with USB Accessories
The E12 has drivers to support many USB devices, such as a second SNAP-powered bridge (using an SN220 or
SN132 carrier board), Wi-Fi devices, cell modems, or external storage. While the complete details of configuration
options available on these devices fall outside the scope of this document, there are some common considerations
that may prove useful.
USB Power
The USB 2.0 connection on the E12 is not rated as a “battery-charging” connection, and may not provide sufficient
current for high-drain devices, such as some external hard drives.
If you find you are having problems with your USB devices (e.g., external hard drives failing to mount, or cellular
connections losing their connections), we recommend you try connecting the device to the E12 through a powered
USB hub.
Connecting to an Additional SNAP Device
The E12 can support a second SNAP-powered node through its USB port. You can connect an SN132 or SN220
SNAPstick, or you can use an FTDI USB-serial cable to connect to an SN171 ProtoBoard or some other hardware that
uses a DE9 connector to make an RS232 serial connection.
This can allow your E12 to act as a bridge between two radio subnets, where radios are on some combination of
different frequencies, different network IDs, and/or different channels.
The E12 provides the drivers that support the FTDI USB-serial cable and the SN132 inherently. To use the SNAPstick
SN220, you need to modify it to operate as a serial device rather than a USB device. For instructions on doing this,
refer to the Synapse Wireless technical brief “Configuring an SN220 SNAPstick as a COM Port,” available on the
Synapse developer microsite at
http://developer.synapsewireless.com/
.
Whichever device you use, plug the device into the E12’s host USB port and (among other messages) you should see
something similar to:
usb 1-1: FTDI USB Serial Device converter now attached to ttyUSB0
or:
usb 1-1: cp210x converter now attached to ttyUSB0
The key here is the line that says “converter now attached to ttyUSB#” (ttyUSB0, in the example shown). You will use
this device handle, “ttyUSB#”, to communicate with the SNAP device. In your SNAPconnect application, you would
open a connection to the device like this:
com.open_serial(type=SERIAL_TYPE_RS232, '/dev/ttyUSB0')