A single board with no components yet added.While we wait for all the boring stuff to happen we thought it might be of interest to cover how we went from the initial idea to a fully working product.
A batch of boards, ready for separating into singles before being loaded into the pick and place machine.
Kitronik Bluetooth Amplifier Beginnings:We’d had a number of requests from Teachers to produce a Bluetooth Amp that students could use as a basis for their design and technology amplifier case designs. Nearly two years ago we built a working prototype using the Bluetooth modules that were available at the time but we determined that releasing a product that was certified for use in the EU and USA was too expensive with the parts we had available to us. Since our first design the cost and functionality of fully certified Bluetooth modules have dropped to a point that means we can offer a high quality and low price product to our customers.
A fully loaded board, programmed and tested and ready to pair.
Initial Design Aims:We wanted the kit to have an impressive sound quality so we opted for the PAM8008 which is also used in our 3W amplifier. There are many benefits of using this modern class-D amplifier, one is that the low working voltage (2.2V to 5.5V) means we can power the kit from microUSB, such as a mobile phone charger. It also lets us use an optional LiPo battery at 3.7V so the kit can be truly wireless! The Bluetooth module on the PCB has some really nifty features too, it has a built in regulator so it can share a 5V power supply with the Amplifier IC and also a LiPo charger so it can handle power management of the optional LiPo battery. The module can even feed back battery information to your phone (iphone only so far) so your phone can tell you if the kit needs charging.
The completed kit is very small and neat, allowing for compact case designs.
An Overview Of The Design Process:We made a list of features we would want from a Bluetooth kit: stereo (2 channels), small form factor, easy to solder to pads for the speakers, large comfortable power switch (my Bluetooth amp at home has a small awkward switch), ease of use and so on. Then started looking at components that could deliver these features. There’s a lot of work in picking the right parts, a good design delivers all the features of the design brief with as few parts as necessary.
An example of a 3D printed case design to house the Bluetooth Amp and Speakers.
How The Initial Design Aims Evolved:The initial design worked reasonably well, it played music and paired to a phone however it required the pressing of a pairing button on the Bluetooth kit to switch the module to pairing mode each time the kit was turned on. This got tiresome in the testing process so we decided we didn’t want to inflict it on our customers so with a bit of re-programming we adjusted the Bluetooth module to automatically enter pairing mode whenever it is powered on (unless of course it is already paired.) When powered on, it also automatically pairs with the last device it was connected to. This means you don’t have to go hunting through the Bluetooth settings on your phone each time you turn the kit on to pair. There were a few cosmetic changes too, the first attempt was larger and more rectangular but we managed to save some space with clever routing which helps bring the price of the PCB down and also makes it more compact and neater to fit into your projects!
A test rig prototype for programming new boards and for making sure they work.
Product Testing Process:The testing process varies depending on the product. As the Bluetooth kit is quite complex the testing needs to be very thorough. This includes testing at a wide range of voltages, from a battery and through the micro-USB connector. Pairing with a variety of devices from different manufacturers, testing with different speakers and different music (to test bass and treble response). That’s on top of the standard testing that all the boards with any pre-soldered parts we produce receive. We will be releasing details of pricing and a release date very soon. To ensure you are the first to know, sign up for our newsletter here.
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