MP3 amplifier module

This tutorial shows how to power up the MP3 playback module with 2 W amplifier for the first time. The module is standalone: it has its own MP3 decoder and is controlled with the four buttons on the board, so it does not need any development board or any program.

You can use it for a music box, a doorbell with its own melody, an audio guide or an acoustic signal. Copy the MP3 files to a card or a stick, connect a speaker and power the board.

How it works:

At power-up, the MP3 decoder searches for files on the available media. By default it uses the TF card, and if there is no card in the slot, it switches to the USB stick. The MP3 files are converted into an audio signal, which goes to the 2 W mono amplifier and then to the screw terminal for the speaker. The same audio signals are also available at the 3.5 mm jack socket.

For a 4 Ohm speaker, the power of 2 W corresponds to an RMS voltage of about U = square root of (P x R) = square root of (2 x 4), that is approximately 2.8 V, and to a current of I = U / R, that is approximately 0.7 A at maximum volume peaks. For this reason, a 5 V USB adapter rated at 1 - 2 A is useful. A weak adapter may produce distortion or restarts at high volume.

Playback starts automatically when power is connected. LED1 stays lit continuously when the module is powered but not playing, and it blinks during playback. At startup, repeat of the entire list is active.

Connection:

Power the module at 5 VDC from a USB adapter through a Micro-USB cable. The board can also be powered from a 3.7 VDC Li-Ion battery connected to the BAT+ and BAT- pads, but for the USB stick, powering at 5 VDC is recommended. The speaker connects to the screw terminal, with the red wire (+) to terminal 1 and the black wire (-) to terminal 2. The module has no logic pins, so there are no 3.3 V or 5 V levels to adapt.

Buttons, controls and indicators:

Volume: start playback, then hold Next / V++ for about 2 seconds to make it louder, or Prev / V-- to make it quieter. The change is heard immediately from the speaker, repeat the press until you reach the desired level.

Changing tracks: a short press on Next / V++ goes to the next track, and one on Prev / V-- goes to the previous track. The change is heard immediately.

Source: when both media are inserted, long press P / P / Mode to switch from the card to the stick or vice versa. The module starts by default on the TF card.

Repeat: at startup, repeat of the entire list is active. Briefly press Repeat to repeat only the current track, and another press returns to repeating the entire list.

Configuration:

Step 1: format the card or the stick as FAT32 and copy the MP3 files, preferably to the root directory.

Step 2: insert the medium into the TF slot or the USB-A port, then connect the speaker and the power supply.

Step 3: check that LED1 blinks and that music is heard, then adjust the volume with long presses on Next / V++ or Prev / V--.

After each restart the module returns to the default mode: TF card source (or the stick if there is no card) and repeat of the entire list.

Usage example:

The goal is a music box that plays the songs from a card in a loop. Copy the MP3 files to a MicroSD card formatted as FAT32 and insert it into the TF slot.

Connect a 4 Ohm, 3 W speaker: the red wire to terminal 1 and the black wire to terminal 2. Power the board from a 5 V USB adapter rated at 1 - 2 A through a Micro-USB cable.

Playback starts automatically and LED1 blinks. Hold Next / V++ until the volume is suitable. Keep the default repeat to play all tracks in a loop, or press Repeat once if you want to repeat a single song.

Common problems:

No sound at all: check that the speaker is connected to the screw terminal (the wire strands firmly clamped in the terminal) and that the files are in MP3 format. Other formats are not played. Also check that LED1 blinks, otherwise playback is stopped or the medium does not contain valid files.

LED1 stays lit continuously: playback is stopped. Briefly press P / P / Mode. If no tracks start, check that the medium is formatted as FAT32 and that the files are copied correctly.

USB stick not recognized: use a 5 VDC power supply, because some sticks do not work correctly at 3.7 VDC. The module has been tested with sticks up to 32 GB and cards up to 16 GB.

The module plays tracks from the card when you want the stick: the card has priority at startup. Long press P / P / Mode to switch to the stick.

The sound is distorted at high volume: use a 3 W, 4 Ohm speaker, an adapter of at least 1 A and reduce the volume with long presses on Prev / V--.

The module does not respond through the USB cable: the MicroUSB port serves only for power supply, control is done with the buttons on the board.

Limitations and tips:

The module plays only MP3 files and has a single amplification channel, with 2 W output, so it is not suitable for stereo playback. For louder sound or stereo, use the jack socket with an external amplifier.

Control is done only with the buttons on the board, and there is no direct selection of a specific track. For external control, the button contacts can be pulled to ground through a switch, a transistor or an optocoupler, with a common ground.

For stable results, use short speaker wires, a stable 5 V power supply and a good quality card. You can go further and build music boxes, doorbells or sound announcements triggered by an external contact.