Bluetooth speaker

Discussion in 'The Projects Forum' started by claymca, Feb 1, 2014.

  1. claymca

    Thread Starter New Member

    Feb 1, 2014
    I am attempting to build my own Bluetooth speaker. I know i could buy one and save myself a headache but it gives me something to do. I want to mimic this version seen in this youtube video:

    The difference is i want to charge the batteries in place and also be able to run the speaker while connected to AC.

    Block Diagram

    The amp:

    The battery is one of the sticking points. I am considering something like this NiMH 18V 4200mAh High Capacity Battery Pack for the battery. Or maybe these in a holder UltraFire Protected 18650 3.7V 2400mAh Lithium Batteries. Six of these series provide about 25v due to the max charge of the individual battery being 4.2v.

    The Step-down buck convertor is simialr to this:DC-DC dual double output 7-16V Step-down BUCK convertor

    The 2nd sticking point is the charging circuit.
    Is there a PCB already built that I could use to charge the batteries and use the AC power while the battery is charging? Or can I use a switching power supply?

    Just looking for some advice or a point in the right direction. This doesn't need to run for 12 + hours. Just some thing to use around the house while, for example, folding clothes in the laundry room and watching netflix on the iPad and i need a little more volume than the iPad speaker.

    Thanks in advance.
  2. claymca

    Thread Starter New Member

    Feb 1, 2014
    Any thoughts? Do i need a battery charging module or would a switching power supply be enough as longs as the battery pack has the protection circuit built in? And would the power supply need to be a little higher voltage to properly charge the battery
  3. wayneh


    Sep 9, 2010
    Given the two choices, I might opt for the higher capacity choice, or maybe the highest capacity per dollar option. It would be helpful to estimate the current draw, so you know how run time you would get from the different options. IMHO, your unlikely to need more than, say, 5 hours on a charge. So if the smaller capacity (cheaper?) option is good enough, go for it
    The 2nd sticking point is the charging circuit.
    The short answer is yes. But the details will depend on battery you choose. The switching from battery to AC is often accomplished with a power jack with a switch built in. You could still suck AC power off to charge the batteries, but power to the speaker would have to come from the AC source while it is plugged in.
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
    I recommend going to a 12V lead acid (sealed) battery which is pretty easy to charge and tolerant of overcharge. You could charge it from a wall wart with a series resistor.

    There are a lot of cheap decent sound audio chips that run off 12V like the TDA2003 or newer devices. The good thing about them is they are made for auto use and can drive very low impedance speakers (like down to 1.6 Ohms).
  5. claymca

    Thread Starter New Member

    Feb 1, 2014
    The problem with the SLA batteries is the size. I want to make this portable and keep the weight relatively light. I also want to power the amp and bluetooth module from the same source.
    Last edited: Feb 2, 2014