LM386 is a mono amplifier IC. I couldn’t find a stereo version of it that was just as robust and simple. So, I designed a circuit with two LM386 chips. That was several months ago.
In the meantime, my BlackBerry Playbook refused to charge. Because of disuse, the battery deep-discharged. There are many videos online offering all kinds of solutions but none worked for me. BlackBerry decided, in their infinite wisdom, to control the charging process using a novel logic, which absolutely refused to charge the battery if the voltage went below some limit. After dismantling the tablet beyond repair, I realized that I could have saved the tablet by opening the plastic cover & directly charge the terminals.
Well… I then had two good tablet batteries and a broken tablet. I decided use it for something. These were high-capacity batteries but like phone batteries output only 3.7 volts.
I got a phone battery charging circuit board that took 5 volts in. It has two LEDs – charging & fully charged. The board also has two load terminals from which you could draw 3.7 volts just like a phone would.
My MP3/FM module requires 5 volts so I added a voltage boost (step up) circuit board.
My attempts to repurpose USB cables from discarded devices failed because they burned off internally during soldering. Hence, I fashioned my own USB cable.
I made a wooden housing for the player. The speakers have neodymium magnets and sound super loud. This is interesting because the stereo LM386 amplifier circuit runs off the same 5 volts. The MP3 module has FM, SD card, line in & USB. It is the same kind as those cheap Chinese FM/MP3 amplifier sets found in autorickshaws.