Overview

The RN-52 Audio Bluetooth Breakout is a sleek Bluetooth audio module from Roving Networks broken out on an easy to use PCB. It allows you to send stereo audio over a wireless Bluetooth connection. The module has an embedded DSP that handles the audio stream entering and exiting the module, converting the digital wireless signals into audio and vice versa. The module is easy to configure with both ASCII commands and GPIO. It can function as a stand alone module, or it can be incorporated with a microprocessor to create the ultimate wireless audio experience.

Covered in this Tutorial

In this tutorial, we will go over some of the module’s features. We’ll show you how to configure the module to suit your projects needs, how to hook it up, and go over a simple example project using the RN-52.

Suggested Reading

• Bluetooth Basics
• Serial Terminal Basics
• What is Arduino?
• Serial Communications
• How to Use a Breadboard

The RN-52 Module

Before we get in to the breakout board, let’s discuss the module and its features.

As with any product, it is wise to read the datasheet before embedding this device into a project.

Bluetooth Version

The RN-52 is a Bluetooth v3.0 module. It is compatible with all Bluetooth v3.0 devices and also backwards compatible with all Bluetooth v2.1 + EDR, 1.2, and 1.1 devices.

Bluetooth Profiles

Here is a list of all the profiles that the RN-52 supports.

• SPP - Serial Port Profile allows you to configure the device over a UART serial connection. This can also be used to send commands to the module from a microcontroller.
• HFP/HSP - Support of both Hands-Free Profile and Headset Profile mean the module can act as a headset device. This allows the it to send audio back and forth, just like a Bluetooth headset. You can send audio input through a microphone and receive audio output through a speaker or headphones.
• A2DP - Advanced Audio Distribution Profile sends audio in one direction, but the quality of that audio is better than the quality of HFP and HSP.
• AVRCP - A/V Remote Control Profile allows you to control certain features of your audio through the module. Tasks such as Play/Pause, Volume Up, and Volume Down can be controlled by inputs on the module.
• iAP - This is the iPod Accessory Protocol, and it allows you to connect the module to any Apple devices such as iPhones, iPods, and Mac laptops and computers.

*Note: Multiple profiles can be implemented at once. The default settings are set to have all profiles discoverable.

Range

The RN-52 is a Class 2 Bluetooth device, meaning that the range of the on board antenna is about 10m. Thus, you should be able to stream audio to the module from about 32 ft in open air. If you are streaming through walls or windows, that range will diminish.

Wireless Audio

The RN-52 is different than other Bluetooth modules in that it can stream audio. It does this via an on-board Digital Signal Processing (DSP) chip. When streaming audio to the RN-52, the DSP converts the radio waves sent from the transmitter device (phone, computer, etc.) into electrical signals that can then be sent to the amplifier and then to your audio output (speakers/headphones). When streaming audio from the module, it converts the electrical signals from the audio input device (mic/line-in) to radio waves for the receiver device (stereo, computer, phone).

Many people ask why it isn’t possible to send audio over just any old Bluetooth connection. The lack of an on-board DSP is the main reason most “regular” modules cannot support audio streaming.

Communication

Aside from a wireless Bluetooth connection, the RN-52 has four paths on which it can communicate to outside devices: UART, USB, SPI, and PCM. We’ll discuss these in more depth in the next section.

The RN-52 Breakout

There is a lot going on with the RN-52 breakout board. Let’s break it up into sections to find out what pins are needed for what purposes.

Here is the module broken up into sections by color (and numerically for the color-vision impared).

1. Power

Powering the RN-52 is very simple. There are three pins necessary to power the board, 3.3V, GND, and power enable (PWR_EN). The supply voltage should be in the 3.0 ~ 3.6V range.

2. GPIO Pins

The RN-52 has eleven general purpose input/output pins (GPIO). Many of these pins are reserved for special functions when the module is booted up and when the module is running. These pins also act as input pins for specific functions during audio playback. These can be configured to control media programs such as iTunes or Windows Media Player (eg. Play, Pause, Next Song, etc.).

This table shows each GPIO and its function.

The most important pin to take note of is GPIO9. If you are familiar with other versions of Roving Network’s Bluetooth modules, you may also be familiar with the $$$ command used to enter command mode on the module. On this module, however, there is only one way to enter command mode, by pulling GPIO9 LOW.

There is also one analog input/output line, AIO0.

3. USB

The USB lines are strictly used for device firmware update (DFU) mode. Used in conjunction with GPIO3, the USBD+ and USBD- lines allow you to upload new firmware directly to the RN-52.

4. UART

The UART lines are used to communicate with and configure the RN-52. Used in conjunction with GPIO9, the UART will allow you to send and receive serial commands to and from the module.

The UART can also be used to connect the module to an external microcontroller that issues commands and handles status updates.

5. Audio In/Out

These pins are reserved for audio input and output. The RN-52 comes ready to stream audio right out of the box. You can attach speakers directly to the speaker pins and get immediate gratification from wireless music. The RN-52 has a built in integrated amplifier capable of driving two 16Ω speakers or most standard headphones. The speaker outputs can also be attached to an external amplifier for greater amplification.

The RN-52 also supports audio input on the Mic pins.

6. Status LEDs

There are two status LEDs located on the breakout board. However, if you wish to place the board in an enclosure, these lines are broken out for external LEDs. The LEDs are configured as open drain output, meaning that they must be driven HIGH to activate the the LED.

Note: Flashing refers to the LEDs flashing alternatively. If you see the LEDs flashing in unison, then you are in DFU mode. Please check pin 3 if you have entered DFU mode by accident.

7. SPI

External audio codecs can be sent over the SPI lines.

8. PCM

Another option for communicating with the module is the Pulse-Code Modulation (PCM) pins. PCM is a way to digitally represent sampled analog signals. This is done over an I2S connection. External audio codecs can be sent over these lines as well.

Hardware Setup

Before you can configure the module, some hardware needs to be connected. This section will cover the necessary hardware needed to work with the RN-52.

Materials Needed

Aside from an RN-52 Breakout, you will need the following:

Wiring the RN-52

In order to use the RN-52, you must first decide how you will connect external hardware to the breakout board. One option is to solder female headers to both sides of the breakout. Second, you can solder wire directly to the breakout. Another option, and the one that will be used in all the demos in this tutorial, is to solder straight male headers to the breakout so that it can be used in a breadboard.