■ PHOTO 1. There’s no sense in trying to pick
out who’s who in this shot as we can’t alter the
operation of the radio or the VEmesh controller.
Trust me. This is the business end of a VEmesh
Node and Gateway.
in our possession are limited to UART and USB
interconnects. UART-enabled VEmesh Nodes are
designed to interface to a sensor’s output via the
Node’s RS-232-based interface. The Nodes with a
USB portal are intended to be connected directly
to a PC USB port which is emulating a standard
PC COM port. The protocol of choice is RS-232
EIA serial data transfer using TTL logic levels. The
VEmesh evaluation Nodes and Gateway are
preprogrammed for a baud rate of 19200 bps.
The heart of a VEmesh Node is under the
lens in Photo 1. I figure the radio IC is to the far
right of the shot as I can trace paths from the
UART interface directly to the Texas Instruments
part on the left.
inbound from the wireless sensor network nodes — the
Gateway sees it first. A message can be data, a command,
or a response to a command.
While a VEmesh Gateway’s job is to interface wireless
sensor network traffic to a host management application,
the VEmesh Node is born to do the down and dirty work.
VEmesh Nodes interface directly to a sensor or sensor
array, and are responsible for relaying data between nodes
and to and from the host management application.
Almost any type of sensor communications interface
can be adapted to a VEmesh Node. The evaluation nodes
THE VEMESH NODE
The VEmesh Node’s UART interface consists of a
UART_RXD input, a UART_TXD output, and a UART_CTS
output. The aforementioned UART signals are located on
the Node’s J10 connector as pins 4, 6, and 8, respectively.
Pin 10 of J10 is the UART interface ground connection. A
macro view of J10 is shown in Photo 2.
All of those USB discussions we’ve had in past Design
Cycle offerings have paid off in that we already know how
the FTDI FT232RQ USB interface IC you see in Photo 2
works. In this case, the USB interface is used to turn the
VEmesh Node’s UART interface into a USB interface that
is supported by a PC COM port. The inclusion of the USB
interface allows us to use a terminal emulator program
such as Tera Term Pro to imitate the output of a sensor
that would normally be attached to the VEmesh Node.
The evaluation firmware loaded on the Nodes and
Gateway is coded to allow the transmission and reception
of one to 20 ASCII characters. The end of the ASCII string
is delimited with a Carriage Return (0x0D) and Line Feed
(0x0A) character pair. ASCII character transactions allow
us to use Tera Term Pro to send data via a PC keyboard
and receive results in human readable form.
There are two VEmesh Node operating modes that
we can select with the four-position toggle switch array.
Standard mode is as close to a real-world VEmesh wireless
■ PHOTO 2. The VEmesh Node UART interface is pinned
out on J10. Note the use of an FTDI USB interface IC for
the PC connection.