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RN-42 Bluetooth Module (#30086)
The RN-42 Bluetooth Module provides a reliable low-cost method for wireless communication interface
between two devices such as a microcontroller, PC, cell phone or another module. This module can pair
up with devices supporting Bluetooth SPP (Serial Port Profile) to establish a serial interface. The RN-42
Bluetooth Module is breadboard friendly and is compatible with all 5 V and 3.3 V microcontroller
platforms.
Features
Fully qualified Bluetooth 2.1/2.0/1.2/1.1 module
Low power
Auto-discovery/pairing
Auto-connect master mode
Compatible with 5 V and 3.3 V microcontrollers
LED indicators for status/connection
9600 default baud rate
Jumper-select 115K baud rate or adjust to custom
baud rate in software
Key Specifications
Power Requirements: 5.0 VDC or 3.3 VDC @
~5 mA sleep; ~15 mA idle; ~20 mA transmit;
~50 mA max
Communication Interface: 5 V / 3.3 V asynchronous
serial interface with RTS/CTS flow control, from
1200 bps to 921K bps
Operating temperature: -40 to +185 °F
(-40 to +85 °C)
Dimensions: 2.33” x 1.16” x 0.45” in
(59.18 x 29.46 x 11.43 mm)
Application Ideas
Remote control a robot via PC, cell phone or another
microcontroller
Cable replacement (wireless serial interface)
Measurement and monitoring systems
Industrial sensors and controls
Copyright © Parallax Inc.
RN-42 Bluetooth Module (#30086)
v1.0 2/6/2013 Page 1 of 6
Quick-Start Circuit
Figure 1: 5 V microcontroller
Figure 2: 3.3 V microcontroller
Set the module voltage to 5 V or 3.3 V to match your microcontroller system, using the voltage selection
jumper as shown above. Connect VIN and GND as shown above, and then connect RX, TX, RTS and CTS
to available I/O pins on your microcontroller. If you do not wish to use flow control you can connect
RTS/CTS together instead.
Important Information
BE SURE VOLTAGE JUMPER IS SET PROPERLY (5 V OR 3.3 V) BEFORE APPLYING POWER!
Please see the RN-42 Advanced User Manual for complete command listing.
The 4 unused pads in the top left corner are for factory firmware programming and are not
useful to the end-user.
Specifications
Symbol
V
IN
V
IN
I
VIN
―
Quantity
Supply Voltage ¹
Supply Voltage ²
Supply Current ¹
Operating Range ³
Minimum
4.8
3.2
5
36
Typical
5V
3.3
15
55
Maximum
5.2
3.4
50
60
Units
V
V
mA
Feet
1. When supply voltage jumper is set to 5V
2. When supply voltage jumper is set to 3.3V
3. Approximate readings in office environment, throughput and range may vary depending on
environmental conditions and RF interference
Copyright © Parallax Inc.
RN-42 Bluetooth Module (#30086)
v1.0 2/6/2013 Page 2 of 6
Pin Definitions and Ratings
Pin
1
2
3
4
5
6
7
Name
GND
VIN
RST
RX
TX
RTS
CTS
Type
G
P
I
I
O
O
I
Function
Digital Ground
5V or 3.3V power input (must be regulated)
Resets the device when brought to GND (0V)
Receive data input to RN-42 UART
Transmit data output from RN-42 UART
Ready To Send output from RN-42 UART
Clear To Send input to RN-42 UART
Pin Type: P = Power, G = Ground, I = Input, O = Output
Communication Protocol
The RN-42 Bluetooth Module communicates using asynchronous serial and supporting RTS/CTS flow
control. If you do not wish to use hardware flow control or your device does not support it you may tie
the RTS and CTS lines together on the RN-42 Bluetooth Module.
Command Set
The RN-42 Bluetooth Module command set is similar to the industry standard Hayes AT protocol. For a
complete command reference supported by this module please see the RN-42 Advanced User Manual
which can be downloaded as a PDF file from the RN-42 Bluetooth Module product page.
Configuration Jumpers
The RN-42 Bluetooth Module has four sets of configuration headers as shown below. Note
the order of the jumpers. Two shorting (shunt) blocks are included to allow enabling
different features of the RN-42 Bluetooth Module. The extra shorting block is hanging off
one pin on an unused jumper.
Default Baud Rate (4)
OFF = 115K default; can be overridden by software baud rate configuration commands
ON = 9600; ignores software baud rate configuration. Default setting is ON.
Auto Master (3)
ON = Device acts as a Bluetooth master, auto-connecting to a stored remote address. First you must set
the address of the slave device using the SR command or through instant cable replacement settings.
Default setting is OFF.
Auto Discovery (2)
In slave mode, sets a special class of device that is used by the master to auto connect. If jumper 3 is
also ON, the device performs a search, stores and connects to a remote slave which also has jumper 2
ON. Default setting is OFF.
Factory Reset (1)
Set this jumper ON, power up unit, then toggle the jumper from ON to OFF three (3) times to return the
unit to factory settings. Default setting is OFF.
Copyright © Parallax Inc.
RN-42 Bluetooth Module (#30086)
v1.0 2/6/2013 Page 3 of 6
LED Indicators
The RN-42 Bluetooth Module has three LED indicators which
give feedback to the user. The functions of these LEDs are as
follows:
Green LED (STAT)
This LED’s blink rate indicates device status :
10 x per second = In configuration mode
2 x per second = Boot up, remote configurable
1 x per second = Discoverable/Idle
On Solid = Connected
Note: When performing a factory reset the green LED flickers at power-up and once again at the end of
the reset sequence. This helps indicate the module was successfully reset. See the previous section on
configuration jumpers for more information.
Blue LED (LINK)
When lit, this LED indicates that the RN-42 Bluetooth module has established a communication
connection with the remote device.
Red LED (DATA)
Blinking 1 time per second = Data over the UART. This LED only functions during the remote
configuration timer window. What this means is that once the module goes into fast data mode and
cannot be remotely configured the LED will stop blinking.
Pairing/Connecting
When pairing the RN-42 with another device such as a laptop or cell phone the default passkey is “1234”.
The device is discovered as RN42-xxxx (where xxxx is the last 4 digits of the device MAC address). On a
PC with Bluetooth the device will have a COM port assigned to it. When this COM port is opened the PC
should reconnect to the module (the Blue LED should light up). At this point you can send/receive serial
data.
Connecting via Bluetooth from a PC may vary with different computers and version of the operating
system, however there should be a method to add the device and assign a COM port to it. When given
the option you should always choose to use the pairing code so that in future connections it does not
prompt you for the code.
When connecting from module to module using two microcontrollers, jumper 1 is ON to force the baud
rate to 9600 bps. If you set the software baud rate you won’t need to set jumper 1 to ON. This will free
up both jumpers for one of two auto-connect modes.
Auto-Master
Place a shunt on jumper 3 to make the device acts as a Bluetooth Master, auto-connecting to a stored
remote address. First you must set the address of the remote (slave) device using the SR command or
through instant cable replacement settings. See the RN-42 Advanced User Manual for more information.
Auto-Discovery
Place shunts on jumpers 2 and 3 to configure the device as a master module. At power-up a master
module will search and attempt to connect to another (remote) RN-42 Bluetooth Module which has
jumper 3 ON. See the section on configuration jumpers for more information.
Copyright © Parallax Inc.
RN-42 Bluetooth Module (#30086)
v1.0 2/6/2013 Page 4 of 6
Troubleshooting
Always be sure of your power source. You should have a regulated 5V or 3.3V source and the
power supply selection jumper must be in the correct position.
If you’re having trouble with communication be sure your baud rate is set correctly.
Be sure your microcontroller TX pin connects to the RN-42 Bluetooth Module RX pin. Your RX pin
should connect to the TX pin on the module. (Not TX to TX or RX to RX)
If you cannot connect using the Auto-Master mode (using the stored remote address) try the
Auto-Discovery Mode. This could indicate the remote address is not set properly.
Check your jumper settings. Remember, the jumpers are 1 through 4 from right to left, not left
to right as you might expect.
When connecting from a PC, be sure to select the correct COM port. Sometimes windows will
assign more than one port to the Bluetooth device. The one to use is the one in the properties of
the device in the Bluetooth device window. Select to show Bluetooth devices, right-click on your
device and select properties. One of the tabs should list the assigned COM port. This varies
depending on PC make and operating system.
When having communication issues try disconnecting, cycling power on the module and
reconnecting. This can happen when you have just paired with a PC in some cases.
Try a factory reset. See the section on configuration jumpers for more information.
Module Dimensions
Copyright © Parallax Inc.
RN-42 Bluetooth Module (#30086)
v1.0 2/6/2013 Page 5 of 6
