Pinout:

PCB Photos:

Firmware:

Github: https://github.com/DragonRailway/TrainControl_BLE

Specifications

• Microcontroller: ESP32-S3
• Motor Driver: DRV8212 (up to 4A peak)
• LED Control: Directly driven by transistors, supports up to 6 LEDs, onboard current-limiting resistor (100Ω) for each LED
• Audio Output: MAX98357 I2S Audio Amplifier
• Battery Charging: TP4056 Li-ion Charging IC (for 18650 Li-ion battery)
• Protection: Built-in reverse polarity protection, Digital cutoff for over discharge protection.

Circuit Explained:

- LED Drivers:

Each LED is driven by an N channel Mosfet. Also has a 100 ohm resistor for current limiting.

- Motor Driver:

The two motor connectors are wired in parallel to a single DRV8212 driver (capable of supplying 4A peak, more than enough for 4 N20 motors).
Additionally we have a BEMF detection circuit using 3 resistors (function not yet implemented in firmware).

- Audio Output:

There is a MAX98357 on board, look how tiny that thing is. This I2S amplifier has great sound quality compared to the DAC based amplifiers.
The locomotive firmware has no audio, I still included it anyway.

- Power control:

This is essentially a high side switch with physical buttons. There is also a PWR_BTN connected to detect ON button presses.
Pulling PWR_IO high in setup keeps the circuit powered on. When Battery drops below 2.8V - 3V, the ESP32 shuts down thereby protecting the battery from over discharge in case the firmware shutdown fails.

- Safety Features:

The battery charging IC is the common TP4056 configured at 1A charge current.
TP4056 wont cut offf incase the current doesnt fall below 10% of charging current. So when the USB cable is connected, The board will be not be powered by the Battery.
The board is also protected against reverse polarity. This is important since we dont want anyone burning their boards, The 18650 cell can be easily installed in reverse especially when you are sleepy.

Community Collaboration:

When the design was ready, I shared it with the community with this notice. They still went ahead and ordered it, most of them received the boards before me.

Thankfully the board didn't blow up, only the power toggle feature was not working. But a simple workaround was devised to fix that.

Special thanks to @dw5304 (discord); he did most of the testing for this board (Revision 1).

The development was accelerated with the involvement from our community members.

Note:

As of Dec 2024, 5 boards cost $100 (incl. shipping to US)