Go XBee-PRO With
Your Robot Control
Many of you are monthly readers
of both SERVO and Nuts & Volts
magazines. For those of you that
are SERVO-only readers, there are
things going on over in Nuts &
Volts that may be of interest to
you. We’ve been working with a
16-bit PIC24F general-purpose
design in the NV Design Cycle
column that is perfectly suited for
robotic and machine control work.
This month, we’re going to apply
that 16-bit Design Cycle
technology to SERVO-oriented
robotic control applications.
The Nuts & Volts Hardware
The PIC24FJ128GA006-based hardware shown in
Photo 1 speaks for itself. A dedicated ZeroG ZG2100M Wi-Fi module is hard-wired into the PIC along with a 2x16 LCD
and a serial port. The 10-pin header is the RS-232 port
physical attachment point while the 10K potentiometer to
its right is the contrast adjustment for the LCD.
The PIC24FJ128GA006 clocks at 32 MHz using an 8
MHz crystal and the internal 4X PLL (Phase Locked Loop). A
five-volt power supply feeds the Microchip TC1262-3.3 LDO
(Low Drop Out) voltage regulator. I’ve pinned the printed
circuit board’s header pads with standard 0.1 inch pitch
header pins. The breadboard is socketed to accept the
header pins. Both five volt and 3. 3 volt power are available
at the breadboard level.
The NV implementation works well and is based on the
free Microchip TCP/IP stack which drives the ZeroG
ZG2100M Wi-Fi module. In our SERVO implementation,
we’re going to replace the Wi-Fi module with an XBee-PRO
802.15.4 radio. The XBee-PRO RF modules are designed to
be part of low-cost, low-power wireless sensor networks.
54 SERVO 05.2010
By Fred Eady
PHOTO 1. This is a shot of the ZeroG - PIC24FJ128GA006 Trainer
loaded onto a Twin Industries 8100-45-LF prototyping board.
A LCD and serial port were recently added to the system over in
Nuts & Volts.
Drawing a peak transmit current of 295 mA, the XBee-PRO
can attain a range of up to 300 feet indoors and up to one
mile outdoors. To give you a perspective of the XBee-PRO’s
output power, remember the walkie-talkies you had as a
kid? Well, they transmitted voice at 100 m W. The XBee-PRO
transmits data at 50 m W. The XBee-PRO RF module
requires 45 mA receiving and less than 10 µA when its eyes
are closed. We’re going to use the RF module’s out-of-the-box peer-to-peer communications method. However, these
modules can be configured for point-to-multipoint and
point-to-point operation. A mesh network of XBee-PRO RF
modules is self-routing, self-healing, and fault tolerant.
These tiny networks are capable of delivering RF data rates
of 250 Kbps. We’re also going to upgrade the project’s
microcontroller motor with the new 32-bit
PIC32MX795F512H. This PIC is pin-compatible with the
PIC24FJ128GA006 with the exception of the
PIC32MX795F512H’s USB I/O interface. If desired, we
could actually run the 32-bit SERVO configuration with the
Wi-Fi module since the Microchip TCP/IP stack supports the
32-bit PIC32MX795F512H and ZeroG Wi-Fi combination.
The XBee-PRO RF Module
The XBee-PRO communicates with the