Start
• Mavric-II
Board
• Sensor
Board
• LCD
Panel Board •
Sensor & Thermocouples •
Two-Axis
Accelerometer
• Radio
•
Radio
Packet Stategy •
Data
Logging
• Adaptable
System •
Sources and PDF
RADIO
The
AeroComm AC4490 series 900-MHz wireless radio module
provides an inexpensive data link from the race
car back to the pit crew’s computer (see Photo 2).
The data rate for this application is 57.6 kbps.
The packets average 29 bytes updated every 125 ms
and require 2.9 kbps. The extra 49% of the bandwidth
is used for protocol-related transmissions and for
future expansion.
|
(Click
here to enlarge)
|
Photo
2—We chose the Aerocomm Radio Module based on
our power and range requirements. It’s used
as a wireless null modem cable, but it also
can be used in many other specialized networking
modes. |
The
hardware interface was made with one of the hardware
UARTs on the microcontroller in addition to four
I/O pins used for status and control. Even though
the radio requires 3.3 V, the I/O pins on the radio
are 5-V tolerant, so they can be connected directly
to the microcontroller pins.
The
pit crew’s base unit radio was easy to construct.
We mated an AC4490 with a voltage regulator and
RS-232 level shifter to give a standard serial link
to the car’s radio. A little tinkering with a USB-to-serial
adapter gave us not only USB capability, but also
a simple 5-VDC source. We tested the USB base end
on a laptop and found it could communicate reliably
up to three classroom lengths (approximately 30’
through cinder block walls) in the Low Power mode.
