Wednesday 11th June, 2014
What's inside a RailDriver controller? This blog post is the first of a small series of posts about train simulation. These posts are side-effects of some work I'm doing for Human Factors' Transport Simulation Laboratory at the University of Nottingham. Needless to say, all opinions and words in this series are my own: if you take issue with them, they're my fault entirely, not theirs. Contact me and don't bother them!

The RailDriver is a desktop "train controller": it's basically a USB game controller that gives you levers to control your train with, buttons also to control your train with, and a bassy speaker to make the whole thing rumble with the engine noise.

This post is aimed at people who are interested in hacking one of these to act as a basis for a larger cab-type controller, or who are just curious about what's inside. I strongly recommend being content with the photos herein, rather than attempting to take it to bits yourself, unless you're happy with the idea that it might not go back together. The one I have does not at all like coming apart, and it likes going back together even less.

TL;DR: is it hackable? Yes, but mechanically. It is not really sensibly feasible to replace the knobs on the electronic side without serious care. On the other hand, if you can rig up gearing to turn the little grommets in the mainboard appropriately, all should be well.

To take the lid off: take out two screws on either side, three at an angle on the bottom holding the front on, and the three topmost screws on the back. The entire top comes off: there is one small ribbon cable connecting the top to the bottom. It becomes obvious here that there are basically two entirely separate modules inside the case.

The bottom half is just an audio amp for rumble: it has a low-pass filter that can be turned on and off with a jumper, and a compressor that can be turned off with a jumper. There's not a great deal more to it than is visible here.

The top half is where all the control stuff happens. It's the top half I'll be concentrating on in the rest of this blog post.

The little cable between the top half and the bottom seems to carry 5V from the USB supply.

The main board is the dual-board assembly on the left hand side of the photo of the top half of the controller above. At the top of the mainboard there are three connectors. The USB cable is the middle one and can be disconnected: getting it out of the way is handy. Don't do what I did: remember to plug it back in before reassembling the unit. You will be annoyed at yourself if you get it back together and the USB cable is sitting on the other side of the room.

There are two screws at the back edge of the case that hold down the cabling. You can take these out. These will also release the little metal brackets, so don't let them fall out and get lost! You can then unplug the cables to the speed display and to the side pushbutton board. The speed board attaches to the topmost connector of the three in a row (when the board is held with the writing the right way up): the side pushbutton board attaches to the connector that is at right angles to the others.

You can now sensibly remove the speedometer board.

The ICs are 74HC595s, which are 8-bit shift registers. There's one per 8-segment LED display. That, together with the five-pin header connection to the mainboard makes me think that the lines on that header are Vcc, GND, and three signal lines, one for each display: the controller on the main board pushes 8 bits per display down the signal lines which are fiddled with by the shift register.

Which lines are which are left as an exercise for the reader. I haven't checked this is true at all.

The side switch PCB is held in by four screws. These also hold in the plastic tray that keeps the physical buttons in, so undo carefully and don't let all the buttons go everywhere like I did. The board itself just has little rubber push buttons on it.

Holding it up to the light shows it's a pretty standard key matrix so it's probably hackable.

The bottom switch board plugs into the remaining connector on the main board, the middle one of the three. It has lots of screws keeping it in. You will need to undo the leftmost of the four screws that are holding the front of the case on (through plastic tabs) as this is holding down the cable tie. Again, this is just a key matrix.

The actual levers are held in by various mechanical contrivances and I strongly suggest not even attempting to remove them bodily. Instead, remove the mainboard. To do this, undo the three screws in a line between the board(s) and the wall of the case. These go into black plastic. You will also need to pop off the tops of the 'wipers' and 'lights' rotary switch things on the front panel. You may find it helps to undo the four screws that go into black plastic on the lever assembly that's nearer to the board, too. Then, pull the board upwards, bend it very gently backwards towards the case until the top two shafts can be popped out, then wiggle it furiously in a state of frustration until the bottom two do. You'll find yourself with an assembly consisting of two PCBs and a plastic frame in your hand if you haven't broken anything.

Now you can remove the plastic harness thing from the back of the mainboard. This contains the two rotary switch things on the right of the top of the case. Before you do anything make sure you understand how the rotary switches fit into the plastic frame, because they will fall out in a moment. Now, undo the four brass-effect screws that hold on the plastic frame and take it and the rotary switches off if they haven't already fallen off and rolled under something.

The two boards in the board sandwich are actually soldered together by means of the headers J6 (on the chip side) and J7 (n the other side). I'd suggest desoldering from the non-chip side if you must do it, if only because there's less to get in the way. A vacuum desoldering gun will be handy here. Desoldering the pins is very fiddly however, and I don't recommend you do it, first because it's a massive pain and secondly because:

There's actually nothing inside.

There are no electronics on the back board at all. Rather startlingly, what we have here, I think, is a bunch of variable capacitors created from PCB planes and plastic (remember, a capacitor is just two planes with a dielectric). The knobs and levers move the plastic in and out of the space between the plates (note that the area for each bit of plastic is divided into two copper areas) and this changes the capacitance.

That's about all that's inside this thing. I rather like its innards!

I'm going to blithely assert that all you need to do to get it back together is follow the above steps in reverse, except that the wiggling is even more furious and trying to get everything lined up is extremely painful. Caveat haxor.

posted by Rob Mitchelmore, 20:26 (anchor)