RF-to-USB-RD
RF TO USB R EFERENCE D ESIGN U SER ’ S G UIDE
1. Kit Contents
The RF to USB Reference Design contains the following items:

EZRadioPRO® F912/4431 Sensor Node
EZRadioPRO® F342/4431 Dongle
 AAA Battery

2. Introduction
The purpose of this reference design is to demonstrate a very low-power, wireless USB system. The system
consists of two components: a wireless Sensor Node and a USB Dongle. The Sensor Node uses a Silicon Labs
C8051F912 MCU and a Silicon Labs Si4431 radio. The Dongle uses a Silicon Labs C8051F342 MCU and a Silicon
Labs Si4431 radio.
The reference design includes two demo applications which implement some typical usage scenarios. The RF to
USB Network Demo shows how the Sensor Node can be used as a wireless sensor, periodically transmitting
remote sensor data back to the host PC. The RF to USB UART Demo shows how the Sensor Node can be used as
a wireless link, shuttling data between two systems.
The wireless Sensor Node and the USB Dongle are small, simple designs and easy to implement, enabling them to
be inexpensively and quickly added to any system that requires wireless capability. There are very few components
required other than the MCU and radio, and typically expensive components such as a wired antenna and external
voltage regulator are not required.
The wireless Sensor Node operates at 915 MHz and is powered by a single AAA battery and uses the on-chip dcdc converter of the C8051F912 to provide power for the EZRadioPRO® radio and the other components. When the
wireless Sensor Node is not transmitting or receiving data, it can remain in a low-power state where it only
consumes 50 nA. The power efficiency of the Sensor Node allows it to operate on a single cell battery for an
extended period of time. The estimated battery life is seven years, limited primarily by the self-discharge of the
battery.
PC
Network
Demo
GUI
UART
Demo
GUI
Dongle
Network
Dongle
App
UART
Dongle
App
USB
Node
HID
Bootloader
Network
Node
App
App
Firmware
Image
UART
Node
App
EZRadioPRO
EZRadioPRO
Figure 1. System Diagram
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Copyright © 2009 by Silicon Laboratories
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3. Hardware Overview and Setup
Figure 2 and Figure 3 identify the major components of the Sensor Node and the USB Dongle. Both devices come
preloaded with the firmware for the demo applications. When using the demo applications, ensure that the printed
antenna on the wireless board is not covered by the user’s fingers.
UART Interface
Button
Potentiometer
C8051F912
Printed Antenna
Si4431
Figure 2. EZRadioPROF912/4431 Sensor Node
The USB Dongle is powered by the PC through the USB connection. Connect the USB Dongle directly to the PC.
The USB Dongle is HID based and requires no custom drivers to be installed.
C8051F342
Si4431
Printed Antenna
Figure 3. EZRadioPRO F342/4431 Dongle (plastic removed)
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4. Software Setup
There are two applications for use with this reference design: the Network Demo and the UART Demo. The demo
applications are designed for the Windows operating systems as part of the RF to USB Reference Design
installation package.
The RF to USB Reference design Installer may be downloaded from the following web page:
http://www.silabs.com/RFtoUSB
Once the reference design software is downloaded from the Silicon Labs website, extract the executable from the
zip file and run it to install the demo applications and documentation. If the software installed to the default location,
the files are installed to C:\Silabs\MCU\RF_to_USB_RD\. Program shortcuts are also added to the Start Menu
under the Silicon Laboratories folder.
5. RF to USB Network Demo
The RF to USB Network demo shows how a Sensor Node can be used as a wireless sensor to periodically transmit
data to the PC. To run the demo, first ensure that the hardware is connected as described in “3. Hardware
Overview and Setup” and the software is installed as described in “4. Software Setup”.
1. Launch the program, which is found by clicking StartAll ProgramsSilicon LaboratoriesRF to USB
RDNetwork Demo.
2. The USB Dongle serial number appears in the drop-down menu.
3. Click Identify in the application. This will trigger the yellow LED on the USB Dongle to blink, indicating that there
is basic communication between the application and USB Dongle
4. Click Connect to start communication with the USB Dongle. The application might prompt to update the USB
Dongle firmware. Click Yes to continue.
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Figure 4. RF to USB Network Demo Application Initial Screen
5. Insert the AAA battery. If the battery has already been installed, please remove the AAA battery, press the
button for at least one second to discharge the capacitor, release the button, then re-insert the battery. This will
reset the MCU on the Sensor Node. Resetting the MCU will reset the Network application and put the Sensor
Node in the correct starting state for the Network Demo.
6. On the Sensor Node, press the button. This will wake the MCU from sleep mode. The first time the button is
pressed the Sensor Node will attempt to associate with the USB Dongle.The Sensor Node will blink green when
transmitting and may blink red if association is unsuccessful.
7. After successful association, and upon each subsequent button press, the Sensor Node will transmit the
potentiometer position and temperature data from the on-chip temperature sensor. It will wake up twice a
second for 10 seconds to transmit data. After 10 seconds, the Sensor Node will go into ultra-low power sleep
mode until the next button press. The Sensor Node will blink green each time it wakes up and transmits
data.The Sensor Node may also blink red if the Sensor Node does not receive an acknowledgement from the
USB Dongle. The USB Dongle will blink green each time it successfully receives a valid packet.
8. The PC application will designate the first Sensor Node to associate as Node 1. The temperature and
potentiometer setting will displayed in the Node 1 section. Rotate the potentiometer on the Sensor Node while
the green LED is blinking to see it dynamically update in the application.
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Figure 5. RF to USB Network Demo Application During Communication
When the button on the Sensor Node is pressed to initiate communication with the USB Dongle, the Sensor Node
obtains a Device ID. The Device ID is persistent as long as the Sensor Node is powered. If multiple Sensor Nodes
are present, each of them will obtain a unique Device ID. The Network demo supports up to four devices
simultaneously.
The green LED on the Sensor Node blinks to indicate device transmission. The red LED blinks to indicate no
acknowledgement or no association response. If the red LED blinks once the first time the button is pushed, it
indicates that the Sensor Node was not able to associate with the USB Dongle to obtain a Device ID. If this
happens, make sure the USB Dongle is connected to the PC and the Network Demo application is connected to
the USB Dongle.
If the device successfully associated, the green LED will blink twice a second for ten seconds. If the red LED also
blinks, this indicates that there was no acknowledgement received for the Sensor Node’s transmissions. If this
happens, please make sure the USB Dongle is still connected to the PC and the Network GUI is connected to the
USB Dongle. Do not put your finger on the Sensor Node antenna while it is communicating.
To reset the MCU on the Sensor Node, remove the AAA battery, hold the button for a second to discharge the
capacitor, then re-insert the battery. The battery must be removed to switch between the Network Demo and the
UART demo. If the Sensor Node LEDs blink for more than ten seconds, it is running the UART demo. Remove the
battery, and reset the MCU.
If the USB Dongle red LED illuminates continuously, this indicates a hardware error has occurred. Unplug the USB
Dongle from the PC and try again.
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6. RF to USB UART Demo
The RF to USB UART Demo shows how a Sensor Node can be used as a wireless link to transmit data between
two systems. The Sensor Node has four test points for the UART interface, as shown in Figure 6. In order to
perform this demo, an external UART device must be connected to the UART interface. The UART interface
operates at 19,200 baud, 8 data bits, no parity, one stop bit (8-N-1), and no handshaking. The logic level of the
UART is 2.1 V, which is available on the VDD pin. Use the VDD pin to set the voltage level for the external UART
device.
If an external UART interface is not available, the device can be configured for loopback mode by connecting the
TX and RX pins together. In this configuration, any data sent from the PC application will be transmitted to the
Sensor Node and transmitted back to the PC application.
The CP2103EK UART-to-USB bridge Evaluation Kit, available separately, may be used in conjunction with the
Sensor Node to provide UART-to-USB virtual COM port connectivity. The CP2103EK is recommended because it
provides a separate VIO connection, which should be connected to the VDD pin of the Sensor Node UART
connector.
GND TX RX VDD
UART
Figure 6. Sensor Node UART Interface
The following steps describe how to perform the UART demo:
1. Connect the external UART device to the RX, TX, and GND pins of the UART interface, or connect the TX and
RX pins together for loopback mode.
2. Remove the battery from Sensor Node. Press and hold the button on the Sensor Node, and reinsert the battery.
Release the button on the Sensor Node. The LEDs will blink quickly for 10 seconds or until the button is
released. This step configures the Sensor Node to run the UART demo instead of the Network demo.
3. Launch the UART demo, which is found by clicking StartAll Programs Silicon LaboratoriesRF to USB
RDUART Demo.
4. The USB Dongle serial number appears in the drop-down menu. Click Connect to start communication with the
USB Dongle. The application might prompt to update the USB Dongle firmware. Click Yes to continue.
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Figure 7. RF to USB UART Demo Application Initial Screen
5. Type an ASCII string in the Transmit text box and click on the Transmit button. This will send the string to the
Sensor Node which will transmit it to the external device. If the device is configured for loopback mode, the
transmitted data is sent back to the PC.
6. Send data from the external UART device to have it appear in the Receive text box. The received text is
displayed in both hex and ASCII formats.
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Figure 8. RF to USB UART Demo Application During Communication
When the Sensor Node receives any UART data on the RX pin, it will wake from the low power mode and transmit
data immediately. The Sensor Node also polls the USB Dongle once per second. If there is any data waiting, the
Sensor Node will retrieve pending data.
The LED indications are similar to the Network Demo. The Sensor Node green LED will blinks when it transmits
data. The USB Dongle green LED will blink when it receives data. The Sensor Node red LED will blink if it does not
receive an acknowledgement from the USB Dongle. If the USB Dongle red LED illuminates continuously this
indicates are hardware fault.
Note: The UART demo is a point-to-point RF demo. The UART demo does not support more than one Sensor Node.
If the UART communication is not working as expected, test the RF link using the loop-back mode first. Most
problems occur due to incorrect baud rate settings. Use an oscilloscope to check the bit time in both directions.
The UART demo Sensor Node will stop polling after 8 hours of inactivity. This will conserve battery power if the
UART is not used. Press the button to wake up the UART demo after 8 hours. Remove the battery from the Sensor
Node to stop the UART demo.
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7. Additional Information
The RF to USB RD uses a 915 MHz RF link. The demo firmware is written on top of EZMAC® PRO. The RF link
data rate is 100 kbps using GFSK modulation. Both demo applications use EZMAC PRO channel 0.
The output power is +13 dB for both the USB Dongle and Sensor Node. The PCB antennas on both Sensor Node
and USB Dongle are designed for lowest possible cost, not maximum range.
For firmware source code or additional information, please contact MCU support.
http://www.silabs.com/support/
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Figure 9. EZRadioPRO® F912/4431 Sensor Node Schematic Page 1
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Figure 10. EZRadioPRO® F912/4431 Sensor Node Schematic Page 2
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Figure 11. EZRadioPRO® F342/4431 Dongle Schematic
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NOTES:
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CONTACT INFORMATION
Silicon Laboratories Inc.
400 West Cesar Chavez
Austin, TX 78701
Tel: 1+(512) 416-8500
Fax: 1+(512) 416-9669
Toll Free: 1+(877) 444-3032
Please visit the Silicon Labs Technical Support web page:
https://www.silabs.com/support/pages/contacttechnicalsupport.aspx
and register to submit a technical support request.
The information in this document is believed to be accurate in all respects at the time of publication but is subject to change without notice.
Silicon Laboratories assumes no responsibility for errors and omissions, and disclaims responsibility for any consequences resulting from
the use of information included herein. Additionally, Silicon Laboratories assumes no responsibility for the functioning of undescribed features
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