#fleischman

The train my dad is controlling has on board sound. But just as in real life, it's not only the train that makes sound. By adding a MP3 player to the board, we can play random sounds over a train station speaker.

For this project I use a DFPlayer Mini. A $1.50 MP3 player with integrated (mono) amplifier. It uses Micro SD cards to store the sound clips and can be controlled over a UART serial interface (together with many other control options).

I have a soft spot for tiny displays, so whenever a built a project like this, I find a way to integrate a display. The display is just as cheap as the DFPlayer Mini, so I think I can justify the costs.

Now, of course sound and display won't be enough to make it a stand-alone controller. So here's the full feature list:

Arduino Nano Socket

DFPlayer Mini Socket with an external connector for a speaker.

The MAX485 IC to allow the board to talk to the Roco MultiMAUS.

A 0.96" I2C OLED display.

Three SMD LED's that can be used as visual feedback (convenient during debugging).

Three hardware debounced push buttons.

A RJ12 connector to connect the Roco system.

Various JST connectors for additional GPIO ports.

A LM7805 voltage regulator to supply power to all the components.

And with that list in mind, the next step is to draw the schematics for this project.

Download the PDF of the schematics here.

After finishing the schematics, it's time to work on the PCB design. Granted, KiCad hs it's quirks, but in the end you'll be able to design some pretty sexy PCB's.

Along the way, the 3D-render function of KiCad gives you a nice feeling about the end product. I think I am on the right track here ...

After I finished up the design, I send my order to one of the Chinese manufacturers, and within a few days this stack of beauties arrived on my doorstep.

Some solder, some heat and a few bottles of midnight oil later, the first populated board turned out better than expected. I must day I'm really a fan of SMD soldering.

If I would make a second version of this board, I'd integrate the ATMega328 and remove the need for the header pins between the display and the DFPlayer. You know, just to make it look even nicer.

Of course I did goof up at some points:

I used the wrong footprint for the JST connectors. I own boxes of 2.54mm spaced JST connectors, but used the 2mm footprint. Not a big deal: we just solder the wires directly to the board (or order some 2mm connectors if needed).

I added a jumper to disconnect the Arduino from the board's power to allow me to connect it to my computer while it's on the board. Unfortunately I forgot to add a jumper of switch to disconnect the serial lines from the MAX485 IC. This prevents me from programming the Arduino while it's on the board.

I added hardware debounced buttons to the board, but those buttons need to be connected to external buttons. It would be much nicer if I added a connector for this as well. Right now I need to solder some wires to the button pads.

Luckily, none of those points are show stoppers. But if I ever need to order a second batch of this board. It might be worthwhile to make the nessecery modifications.

Next step: work on some code!

I've mentioned it a few times before: Platform.io is the perfect integrated development environment if you want to work with microcontrollers. The "new" VSCode extension makes it even better, since VSCode is my code editor of choice. 

The setup for the embedded software is based around some Manager classes and Controller classes. If you are a regular reader of my blog, you know I used those term only to make my code look more professional. Why? because I have no idea what i'm doing.

Anyway, here's the beakdown of the software:

DisplayController: Responsible for displaying all the nessecery information on the screen. This class creates the user interface.

RandomTimeTask: A class responsible for executing tasks at random time intervals.

SettingsManager: Responsible for the setting settings interface, as well as storing and retrieveing the various settings stored in the EEPROM.

SoundPlayer: Responsible for playing the sound clips via de DFPlayer Mini (MP3 player).

TrainController: Handeling the communication with the train (via the Roco MultiMAUS system).

main.ino: The glue between all the classes mentioned above.

The interface allows you to toggle the three random timers (Auto drive, Train Sound, Station Sound) using the on board buttons. The display will show the countdown towards the the moment the action will be initiated.

The randomly picked delays are within a preconfigured range. By using the random intervals, my dad's train module will get a more natural feel. Because lets face it: when does a train ever drive on the exact schedule!?

The randomly scheduled tasks (RandomTimeTask) are based on the Task library by Makuna. The possibility to build your own Task subclass was a perfect fit for this project.

Aside from the default timer interface, you can enter the setting screen by holding one of the three buttons. This will allow you to configures things like Train ID, Train Speed, Volume, Auto Drive Minimum Delay, Auto Drive Maximum Delay, Train Sound Minimum Delay, Train Sound Maximum Delay, Station Sound Minimum Delay and Station Sound Maximum Delay.

All these settings are stored in the Arduino's EEPROM, so they are non volatile (meaning they remain stored even when the Arduino is powered down).

Building these settings screens was extremely easy using the u8g2 graphics library. It already included all the nessecery input tools and is extremely powerful if you want to built user interfaces on small displays like the used 0.96" OLED.

Here's a small impression of the interface I built for this project:

Of course I couldn't have built this project without the hard work of Philip Gahtow who wrote the awesome XpressNet library. So a big thanks to Philip!

And with both the electronics as well as the software finished, it's time to incorporate the Digital Train Controller into my dad's train module. Stay tuned! :)