PHOTO 6. That SP233ACP works just
like the legacy MAX232 but sans charge
pump capacitors. This lashup is perfect
for adding RF capability to pre-USB
2,400 bps, 4,800 bps, 9,600 bps, 19,200 bps and 38,400
bps. The channels and baudrates are software selectable.
The wireless transceiver module is designed to
communicate with a host microcontroller’s UART using TTL
voltage levels. VDD, GND, TX, and RX are the only physical
connections the SRWF-2501 module accepts.
On-module intelligence for the SRWF-2500 is provided
by an Atmel ATMega88. The ATMega88 is a general-purpose microcontroller endowed with 8 KB of Flash and 1
KB of SRAM. The ATMega88’s Flash contains the Sunray
Technology version of a CC2500 driver, as well as the baud
and channel configuration firmware. The Sunray Technology
CC2500 driver is packet oriented and can only belt out a
full CC2500 buffer per transmission. So, the Sunray module
is perfect for small packet low rate data transfer
It’s a no brainer to deduce that a copilot
microcontroller can be attached to the transceiver’s TTL-compatible serial interface. The ATMega88’s firmware
provides an aim and shoot platform. That is, every character
that enters the module’s TX input is transmitted without
any intervention by the host. Likewise, any data received by
the SRWF-2501 module’s CC2500 is automatically
presented to the RX output.
In that the Sunray Technology module is “smart,” we
can deploy the SRWF-2501 in a number of interesting ways.
For example, Photo 4 captures an
SRWF-2501 module tied to a
Microchip MCP2200 USB 2.0 to
UART protocol converter with GPIO.
This particular configuration allows
the Sunray Technology module to
attach to a PC’s USB portal.
When using the SRWF-2501
wireless transceiver module with a
Look up “handy” in the dictionary and you’ll find that
its definition is Digilent Pmods. If you’ve worked with the
Digilent Cerebot 32MX7, you may have a PmodUSBUART
lying around on your bench. The PmodUSBUART is based
on the FTDI FT232RQ USB-to-UART bridge and is the
replacement for the PmodRS232. The local (LCL) and
system (SYS) jumper points in Photo 5 allow you to control
the power associated with the PmodUSBUART. Basically, if
the equipment that is attached to the PmodUSBUART is
powered on its own, the jumper should be set to LCL.
Otherwise, jumpering to SYS allows the PmodUSBUART to
supply + 3. 3 volts to the attached equipment on its SYS3V3
pin. You can get all of the scoop on the PmodUSBUART
from the Digilent website.
It took quite a while for me to embrace USB. There
may be some of you out there that are still on the fence.
Or, maybe your piece of robotic equipment does not have
USB capability. You can wire up a MAX232 and a sextet of
charge pump/bypass capacitors. Or, you can drop a Sipex
SP233ACP in its place. The SP233ACP doesn’t require any
charge pump capacitors. My
wireless transceiver module is the
subject of Photo 6.
You Can Have
Behold Photo 7. It’s a SRWF-
2500 test board complete with a
Silicon Laboratories CP2102-based
USB portal, a baud rate/channel
PHOTO 7. For those that want it all
and want it right now!
38 SERVO 11.2011