Ages ago I found a mini-MP3 player, that is from at least 2011, my PC doesn't recognize it, it doesn't show up. So it will make a good project for me to try hacking something. I can't find a data sheet for the MCU, it's a BR3188 48-pin, here's the only useful mention I found (not pictured tho)
https://forum.arduino.cc/t/mp3-players-lcd-display-using-with-arduino/415935 The back light for the little LCD matrix display seems 1/2 burnt out. So I have no idea if the thing really works, I don't know the buttons/menu's. Out of circuit it reads 3Meg and 4Meg reversed. On diode test it reads 2.6V. I applied 2.9V @12ma and 3V @27mA, and it's still super dull, even in a pretty dark room. It only looks like there's 1 LED under the screen (I don't mean the lack of brightness). And I can't see any characters on the screen at all. I don't see any cracks or damage either. It's glued down too, the flex cable can't move. Also the LED never lights up from the USB or the battery/bench PSU. It/they normally should any time a button is pressed.
I already lost or tossed it's battery. When powered from USB, it seems 12mA is going to the MCU itself across a resistor, and the RAM and FM radio IC get 3.3V from the MCU (there's no regulators or transistors on the PCB at all). The crystal osc. hooked to the MCU is working.
When powered from where the battery connects, I can't really get it to work at all, even up to 5V it draws no current (0mA on PSU, but maybe some 27uA stby according to a 6.5d DMM). If I hold down the play button, it draws 2-3mA, that may be just a pulldown resistor, but then I did see 3.3V appear on the Ram and FM chip, so some of the MCU must be doing that. And it stops once the button play button is released.
When the USB was connected (and unhooked the bench PSU), I see a wavy 4.3 volts at the battery terminals, so I guess thats the charging voltage. I wonder if the lack of a battery is confusing the MCU. I could try adding another Li batt.
I only scoped the outer legs of the MCU, I'll have to solder on some wires to try and find what else the chip is doing, like talking to the ram/LCD. I see where the USB data goes in, I guess I could try my diff.probe on that. It probably just has some old ebay firmware that my PC doesn't recognize, but the FM chip is from 2011, so thats not very old.
The FM chip uses I2C so for sure the MCU has pins for that.
So to me it sounds like the LED is dying, and the MCU might be stuck on STBY when battery powered and need a reset. But I don't have a datasheet, so maybe I'll get to try bit-banging or some such thing. But I barely know MCU's, or programing.
What else could I try and/or look for ? Once I get some wires on the MCU I'll see if it's talking to the ram/LCD, I did see the RCLK from the MCU to the FM chip working. If all else fails, I have the data sheet for it, so I could try making that kind of radio (after a books worth of programing tho I bet)
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