Dale H and I were talking about this over on What did you do on your layout today. After a few rounds of back and forth, it became clear the discussion needed its own topic.
Let me start off by saying that this type of computer control is not for the faint of heart, but boy, is it powerful stuff. The main reason that I'm using it on my railroad, instead of some of the newer technologies, is that I already own the equipment.
So what is CMR/I? In the most basic terms, it is a hardware system consisting of a bunch of on/off switches connected to a computer by a serial line. The switches come in two "flavors", inputs and outputs. What you can control with them is really only limited by your imagination. For my railroad, I'll be using inputs for detection, to tell the computer where the trains are, and outputs for throwing turnouts and running prototypical signaling. Let's take a look at some of the components that I'll be using. Keep in mind these are more than 20 years old.
Let's start with this gizmo. This converts the RS-232 serial protocol from the computer to RS-422 for use out in the field. My understanding is that it needs to be converted in order to travel the distances needed around the layout. There are newer protocols that can do more, but again this was what was available back when I started.
This is a motherboard. The next three boards plug onto it.
This is a USIC, which stands for Universal Serial Interface Card. This is the brain of each mother board. It packs and unpacks the data for transmission over the serial line. The line connects to the pins on the top, and the bottom plugs into the first space on the motherboard.
This is an input card. It has 24 individual input switches. It plugs onto the motherboard on the bottom, and the inputs from the layout connect to the pins at the top. It reads conditions on the layout, and sends that information back to the computer for calculations, through the above chain of devices.
And, this is an output card. Essentially the same as the input, but with the opposite information flow. It is the workhorse of the system, turning things on and off.
So there you have it, CMR/I theory in a nutshell. Unfortunately, I'm not an electrical engineer, so I know nothing about all those chips. If I was given a blank card and a bag full of components, I could assemble one. I just couldn't tell you why it works on an internal level.
But enough background. I welcome all discussion on this subject from anyone interested, and I'm always interested in learning more if anyone out there has experience with this system.
I'm going to continue my conversation with Dale, but everyone should feel free to jump in with comments or questions and I'll do my best to respond.
Dale, I use GarGraves track, so all my rails are insulated. The second outside rail will be connected to CMR/I input bits and go back to the computer. That information will be processed by JMRI Panel Pro and show up on a video dispatch display with a full schematic of the mainlines, including all the appropriate signaling.
CMR/I stands for Computer Model Railroad Interface. This is a hardware system consisting of input and output bits that is connected to a computer by a serial line. For smaller railroads, Arduino or Raspberry Pi processors could probably do the same functions. Once again, I just happen to own all the CMR/I equipment, more recycling.
JMRI stands for Java Model Railroad Interface. It is free software, CLICK HERE to learn more.
Elliot
I take it that the computer sends out a small voltage and measures resistance or amps? Either 0 or 1 to detect occupancy? Meters I worked on generally use 5 to 15 ma and measure quantity. Thanks for the reply.
Dale H
Not exactly Dale, a DC ground is superimposed over the AC common. That ground signal does the classic wheel / axle jump to close the circuit. The other side is 5 VDC back at the input card which is seeking the ground source to drive the bit high. There are also some capacitors and a diode that filter and direct that track ground before it reaches the card. I'll take some pictures and show you what I have. It might help.
thank you Elliot.
I would like to know how it works, electronics is a hobby of mine.
Dale H
OK Dale, there are the photos, and a pretty good overview of the system.
The next few pictures are of what I call detection panels. What you are looking at is just a tiny corner of one of them. I have 4 of these panels, each is 2' x 4' and has a lot of these individual units on it. I think the layout calls for something like 225, so I may only need 2 and a partial to do the job. Unfortunately, I liquidated a bunch of the input cards years ago, and now I might be a couple short.
These panels were assembled by an electrical engineer for my layout at Mall of America back in the early 90's. He figured all this stuff out. Back then, we ran the trains on DC. I hope my lack of electronic savvy hasn't foiled my plans here. He did leave us a few clues, that's his handwriting in the faded ink.
The 2 terminals with the 12 gauge jumpers going between them, are ground. The one in the middle comes from the track, and the one on the right goes out to the CMR/I input card. The one on the left, behind the huge diode says "scoreboard". That was our nickname for an LED display panel that would show the public where the trains were. No need for that on this layout, no public, and I have something far better in mind. That's part of that JMRI thing. We can expand the conversation to that later.
I took these last two in the hopes of seeing the values on those capacitors. I'll go down there with a flashlight and my glasses if it becomes important. I think they're 1000uF.
I was hoping you or someone else here might be able to shed some light on what the "track" input voltage might be, and even more importantly if it can be taken directly from the track, now that I have gone back to AC power.