Why do this?
- Pulse-width modulation allows smooth operation at slow speeds.
- Set realistic rates of acceleration and braking.
- Set maximum speed to avoid derailments.
- Program operational responses to meet your operating style.
- Control train based on sensors, auto reversing, whatever.
- Because you can, and it is cool.
Step 1: Beg, Borrow, or Build
1. Wii Nunchuk. - The only part of this that isn't "open source" or completely hackable. It is, luckly, relatively inexpensive, easy to obtain (you may already have one on hand), and incredibly versatile. For $20 you are getting:
Countless hours of Nintendo product engineering (priceless)
2. WiiChuck Adapter. - While you can cut your cable to access the wires, your kids will hate you when they go to play Lego StarWars next time. A couple of bucks will get you an adapter and guilt-free access to a software library written by the guy that came up with it (www.sparkfun.com/commerce/product_info.php), or your could build your own using this Instructable.
3. Arduino Microcontroller - You can buy or build one of these. They are easy and fun to use, and with the shields, can be put to a number of uses, repeatedly. They come in a number of variants. I like the newer Duemilanove since it has USB built in. Here is one source: www.adafruit.com/index.php
4. Motor Controller - As versatile as the Arduino is, it can't drive a DC motor on it's own. You can breadboard something together using a H-Bridge chip like the SN754410, as shown here, or buy a shield kit that fits right on the Arduino and comes with software libraries and examples. I'm using one I built from Adafruit shown here.
5. Model Train - (Sold separately). Or any small DC motor you might want to drive. I'm actually doing this for a small "switching puzzle" layout I've got built. It is only 1' x 4', and I want it to be easily (and safely) operated by children. It involves a lot of slow-speed back-and-forth, unlike the typical full-throttle round-and-round stuff. You can learn more about the layout on the last page.
Step 2: Putting the Hardware Together
The connections are as follows:
Arduino: 12V power supply plugged into the 2.1mm jack. The board can get power from the USB connected to program it, but USB cannot supply enough power to run the train. Trust me, I've accidentally tried more than once.
Motor Shield: The two leads from the train track go to the motor shield instead of that cheap plastic transformer made in China. I've got them hooked into the "M1" terminals. Change this, and you will have to change in your program. Certainly not hard to do, just one more got-cha. Another little detail: the white jumper on the "PWR" leads tells the board to get power from the Arduino, which as we saw earlier, is coming from a 12V wall wart. See the website if that confuses you. It did me. Alternatively, you can wire power right into the shield. The voltage doesn't need to be exact. You could even run the wires from your original transformer into the shield and just set it to full power. I think they put out 16VDC or so.
WiiAdapter: Confusingly, this can go into the chuk in either of two ways. The correct way is for the contact on the adapter marked "NC" to go where there is no contact on the Wii. I've got the connector pins going to the Arduino analog pins A2, A3, A4, A5. Again, not set in stone, but will have to match the program. There are some good diagrams and such at todbot's website.
Step 3: Software or Firmware?
The difference between "firmware" or "software" is slight. Your "sketch", or the program you load on to the Arduino could be considered "firmware", but the program you use to get it loaded is "software". To make it worse, people start calling the latter a "programming environment". Confusing, eh? Let's not start talking about "bootloaders", because I don't know squat.
Setting up an Arduino programming environment could be a whole Instructable by itself (I don't see one, so feel free to write it). For now, I'll point you to the "horse's mouth", Getting Started at the Arduino site.
With an Arduino "environment" in place, you are going to need a couple of extra's.
- The motor shield comes with a library called "AFMotor ". You need to down load it from LadyAda's website and place it in the "Arduino/hardware/library " folder. If you breadboarded your own controller, you know enough to write your own functions for it.
- My demo software "WiiChuck_Train_Controller " (attached below). My advice is to paste it into the Arduino environment and save it with a really, really clever name. You'll have to supply that yourself.
- The WiiMote adapter also has a library called "nunchuck_funcs.h " available here . This single file will have to be placed in the same folder as the sketch, something like "Arduino/WiiChuck_Train_Controller " folder. In the newer Arduino environment (0017), it shows both the sketch and the nunchuck_funcs.h on separate tabs (see image).
Update (December 2014):
I had compatibility problems with the newer Arduino versions and switched to a newer nunchuk library from:
Take a look at the demo sketch that comes with it.
Step 4: Just the Start!
With the sketch uploaded, hit the "Serial Monitor" button in the right-hand corner of the "environment". This will let you look at what is going on under the hood, so to speak.
The initial part is just the preliminaries. It assume the nunchuk is plugged and centered. It will also show you the current speedLimit (out of 255), and stallSpeed, which is the lowest setting at which the engine will move. It will depend on your engine and power supply. You can easily change any of these in the "environment" and reload the sketch.
Once you hit the joystick, the monitor will begin to stream variables that will tell you what is going on. throttle is based on the X joystick position with centered = 0 and ranging from about -100 to 100. speedSet is the setting it is trying to reach, and curSpeed is the current setting (out of 255) supplied to the track.
Operator's Manual (Ken's Version):
- Left & right on joystick will move the train in the direction moved. If your engine moves opposite to the way you want, swap wires to track (easier) or change variables FORWARD and BACKWARD in sketch (harder). I guess that is where you find out if you are a hardware or software person!
- When the joystick centered, the train will slowly coast down based on a variable called "drag".
- Z-button applies the brakes.
- C-button is "cruise control". It will light LED 13 on board and hold train at current speed. You can speed up, or hit the brake to disengage it.
That is it. Make it yours. HACK AWAY. Use the accelerometer! Please write some better "firmware" and share it.
I hope that if nothing else, this inspires you to get an Arduino and explore the possibilities! Let me know what you come up with!
Move on to the last step ONLY IF THE TRAIN STUFF INTERESTS YOU.
Step 5: Gratuitous Layout Video and Picture
Other "micro-controller" implementations under consideration for the layout:
IR or CdS sensors at end of tracks to prevent running off the ends (check out www.instructables.com/id/A-very-simple-proximity-detector/).
Use sensors for auto-reversing for unattended layout operation (probably just back-and-forth on center spur).
Micro-controlled throwout operation using servos or this ingenious analog device. Use sensors to prevent throwout operation while train on top of it (causes derailment).
Lady Ada's wave shield to provide audio feedback on events like "off the track" or "on the switch". Unfortunately, you can't stack the wave and motor shields (no enough pins available to run both simultaneously). I may just wire up a single motor controller and use the wave shield.
Let me know what else you think it could benefit from.