Bluetooth Audio Link - An Introduction
The BAL, a development board for Bluetooth Audio devices. With BAL you can do a number of things, ranging from simply connecting your phone or laptop and streaming high quality, pop free, stereo audio from it, to more complex features like connecting a micro-controller, and controlling the connected device via Bluetooth. With an on-board pre-amplifier and pop filter, you can plug in headphones and listen right away, at CD quality.
Since first building this kickstarter page, we have been making ongoing modifications to the design, including the ability to power over USB or the barrel jack, and the change from USB Mini-B to USB Micro-B due to demand.
- Easy to use 3.5mm audio jack output
- Connectable from any Bluetooth enabled device
- FTDI connector to interface with the BAL from the computer
- GPIO all broken out
- SPI and PCM lines also broken out
- On-board pre-amplifier and pop filter
- Barrel jack input
- USB Micro-B alternative power source
- USB Firmware upgradable
- Microphone input
- Supports various Bluetooth profiles, it's not all about audio!
For all you specs nerds out there!
- 3.3V-16V Input
- Maximum Current: 1A
- Typical Current: <500mA
- Good quality noise rejection/filtering from supply to output
For the main chip - the RN52 from Microchip:
- Bluetooth 3.0, class 2 device
- 3Mbps Data Rate (Maximum)
- Operational range of 10m
- -85dBm Sensitivity
- 2.4 - 2.48GHz Frequency
- 44.1KHz Output DAC (CD quality)
- 44.1KHz Input ADC
- Supports A2DP, AVRCP, HFP, HSP, SPP and iAP Bluetooth profiles
- ~150ms typical latency - this spec is not from the RN52 datasheet, as one was not listed, but is our typical experience. Playing local files gives lower latency figures than this, usually unnoticeable, whereas streaming from (for example) YouTube gives mildly noticeable latency.
For the amplifier and pop filter - DRV602 from Texas Instruments:
- Flat frequency response (20Hz - 20KHz)
- Signal to Noise ratio of 102dB
- 2Vrms output into a 2k5Ω Load
- 15μVrms noise output voltage
The simplest function of the BAL is to be used as an audio streaming device, which allows you to convert your standard amplifier/home stereo set-up into a wireless entertainment device. Connecting to the BAL from any of your devices is as easy as you would expect.
Advantages vs. competition
The BAL is the only development board on the market for the RN52 audio streaming module aside from the RN52EK from Microchip which is not only expensive (at over £50 plus postage) but does not contain some of the features we are offering, most notably the amplifier and pop-filter, which are essentials if you wish to implement this module into a high quality stereo system.
All other available similar devices are merely breakout boards, such as the widely used board by SparkFun. These require a lot of effort from you, the end user, before they can be utilised. With the BAL you are receiving an instant solution to an audio streaming problem which then has the potential to be expanded into a much larger project. This is made possible due to the full breakout of the necessary pins, including GPIO, SPI and PCM.
History & Development
The BAL was originally a simple audio streaming concept, designed so we didn't need to plug in phones and computers every time we wanted to listen to audio through our home stereo systems. The initial prototype (above) had its flaws, and was developed into the product we are offering you today, which has had countless upgrades made, including the addition of the amplifier and pop-filter and the breaking out of connections, along with the ability to custom program the firmware and use the BAL in many more applications, such as in conjunction with a micro controller project involving wireless device control.
In the late stages of development, just before we were going to launch we decided to ask the people of the internet what they thought through a Reddit thread. This helped us no end to really fine tune the design and iron out some quirks. The main one being that we now use a USB Micro-B rather than a USB Mini-B connector, by popular demand. You can now also power the board from USB or the barrel jack should you wish.
This project is open source and the relevant files, created with KiCad can be found here:
We are complying with this open source hardware licence:
Risks and challenges
The main challenges for us at this stage are in manufacturing and shipping. We need Kickstarter to gauge interest in BAL and give us the funds, and means, to build the boards and send them to you.
Our design is stable and ready to go, though obviously there is always room for surprises lurking round the corner!
We've never done anything on this big a scale before but we have built the boards in twos and threes so we know how long they should take to manufacture. The prototype we have at the moment has been hand assembled by us, just as the final product will be.Learn about accountability on Kickstarter
- (30 days)