projectDCC

Yet another project in the works. This one is intended to leverage my DCC circuit boards into a interrupt driven DCC I/O system for the Arduino Pro Mini. I actually have all of the software done and tested for both the input and output of DCC signals on my Attiny1634 board but I’ve never actually used a real ‘Arduino’. I’ve always built my own boards so this is a learning experience. I’m probably not going to make it compatible with the larger ‘Arduino’ universe, I’ll just optimize it for the Pro Mini. Anyhow, this project is actually number two on the list, the refurbish of my U25B locomotive is first so I can polish off the main widget code base.

u25B-MainModel

I picked up a cheap Aristocraft U25B in Chessie paint the other day and have been taking it apart so I can rebuild it. The idea is to get from the toy like unit I have into at least a semi-scaled sort of model. The photo above is the closest prototype image I’ve found to what is depicted with this Aristocraft rendition. So I’m stripping it down to the base parts with the idea to install my control system, batteries and sound. And of course, a bit of paint and detail work- it is a bit cheezy with the cast color parts. Yuck. So anyhow, I’m getting there. Below is an image of the original model. More in a later post.

chessie

xmaspcbSMAnnotate

Today I got my order of printed circuit boards from Bay Area Circuits. I promptly populated them with components and powered them all up to see how they would do. Everything works! Very nice! Next step is to install these into one of my locomotives and replace all the breadboards with something clean and production quality.

Pictured, in order, is the 8Amp DPDT relay module, it’s used to reverse the direction of the locomotive. It can be triggered either with a logic one or zero, say from an Ardunio, or from an R/C signal via your generic radio control system. (The logic version is shown, the R/C version has an additional chip on the board, you can see the outline).

Second is the DCC output module. It is designed to be driven with a logic signal from a micro-controller such as the Ardunio. Logic input in, attach your choice of battery (or other) power to the input terminals and it provides up to 3Amps of DCC encoded power on the outputs.

Below that is the DCC input module, connect this to any DCC device like the MRC Prodigy or NCE DCC units and it converts the high voltage DCC signal down to what a micro-controller or Ardunio needs.

The last one is my Control Widget Node. This device is a micro controller wired to an industrial strength Xbee Series 1 802.15.4 Wireless Network Module. I use this for both my Control and Slave nodes. It allows high speed data delivered in an organized network infrastructure with a range of about 300 ft. I send both proprietary packets and DCC messages over this in real time. This is the latest PCB design.

micro

I’ve been doing quite a bit of PCB design these days, here is a version of my controller board, the ‘microwidget’. It’s quite compact. I have not had any made yet but I thought it came out really sort of, well, neat. Like art kinda.

All total I have about five or six small circuits for doing control networks- specifically for large scale model trains. DCC input and output, servo control, DC brushed motor control, reversing relays- all via Industrial strength Xbee Network wireless.

I’m also thinking of making an apt-get debian package to install JMRI on a RPi 2 and gitlab for my code. Hmm.

I think I need a Kickstarter :)

master

P1040664

Here are the final two prototypes. The master obviously connects to the Prodigy Express and sports a long range antenna for max transmission power. What I’m thinking here is this is the module that will be connected to my RPi 2 which I am planning on running JMRI on. The Pi 2 will also have a long range wifi antenna on it so I can use it to source web pages to my phone and tablet. My standard handheld design is what I actually use to drive my trains with.

The second pic is the client. This one is fairly comprehensive and has quite a few parts but I use it as my standard prototype rig. In addition to the control board, it also has an (expensive) Pololu 18v7 motor controller and a current sensor. The DCC output stage is the board with the large chip beside the speaker. All it is used for in this incarnation is to drive the Econami Diesel DCC decoder which powers the speaker on the right.

Here are all the parts labeled, you can click on the picture for a larger version-

client-small

dcc

Well, I didn’t like some things about the DCC output state machine in the last post, the one with the (wrong) zero bit on the end so I refactored it and now it works mucho better. I took the background scan timer down to nothing so it would spit out DCC as fast as possible, this is the trace. The top trace is the rebuilt DCC, the bottom is the output of the Prodigy with just the default 003 loco address, albeit set to 128 step mode. Aside from the lesser number of preamble bits I’m sending they are the same, well within a microsecond or two. I am running this on an Attiny1634R-SU which is the 2% clock. Costs a few pennies more but worth it over the regular vanilla chip which is 10%, a bit loose.

I think the diagram in the last post caused a bit of confusion. Suffice to say I am just breaking apart the components of DCC and the subsequent ‘decoders’. I find the term ‘decoder’ somewhat problematic, I would refer to them as ‘clients’ with the DCC ‘booster’ or ‘cab’ as the ‘master’.

Anyhow, one of the things I do not like about DCC is the power aspect. DCC is sort of a bastard child of both power and data packets which makes messing with it more difficult. I realize that is really important when you carry power on the track but I don’t want to do that. I want the compatibility with DCC accessories and JMRI but I want to run battery power (or maybe steam one day) So I am chopping the power part out and siphoning off the data packets, sending the data out via xbee and rebuilding them on the client. The client takes the battery power, injects that into the data part and out comes DCC. I don’t need much in the locomotive that requires DCC per se, except possibly sound but I am interested in choosing routes via something (JMRI?) and setting turnouts (accessory decoders?) and signals and things like that too so I want all this to work.

Oh yeah, another aspect of DCC I’m finding I don’t like is the slam-bam sort of thing. Well, ‘not like it’ is relative I suppose, it’s probably the easiest one and most ‘organic’ of the protocols. Constantly send everything as fast as possible and you are at least sure some are getting there, right? So I’ve also, sort of, modified this at least over the air. This keeps network traffic low. I currently have only one priority queue in the master, I think I may have to expand this to two later one. A ‘hi’ priority for the locomotive situations and a ‘low’ for other things? Dunno yet.

Here is the Prodigy DCC controlling a servo over my Xbee network. (the video is sped up 200%) This validates the network layer and the speed. However, this is just a raw implementation of the protocol. The DCC message is just sent as fast as possible, regardless if it has changed or not. I don’t want to keep it this fast, there are far far too many Xbee packets flying around. It is ‘thinned’ out a bit because only packets meant for address 8522 are sent to this Xbee but I will need to implement the proper algorithms so that only data that changes is on the network. The client can then maintain the DCC stream on it’s own. Also, with only 128 steps of speed control the precision is lacking controlling the servos smoothly. I’ll need to do some processing of the speed before it’s sent to the servos.

It has a ways to go before it’s a bonafide ‘wireless decoder’ but the basic wireless network works, and that’s the most important, everything else is just more firmware :)

So far, I’ve used less about a third of the flash and ram:
Program Memory Usage : 4908 bytes 30.0 % Full
Data Memory Usage : 215 bytes 21.0 % Full

atmel-Studio7

logicAnalyzer

dccw

Making good progress on this. What I’ve done here is connect my MRC Prodigy Express DCC system to my Control Widget Platform. The input from the DCC system is run through an optoisolator to get the voltage down to logic levels. I then wrote an IRQ routine to decode and assemble the DCC packets. These get queued, error checked and then passed to the Xbee transmit routine. I pull the DCC destination address (either 1 or 2 bytes) out of the packet and use that as the Xbee destination address.

In the Atmel Studio pic above, you can see the Xbee X-CTU utility displaying a stream of Xbee encoded DCC messages for address 8522. Anything addressed to 8522 flows out over the air and into this particular Xbee which will eventually be on the client controlwidget.

In the logic analyzer pic, you can see I’m blasting these out about every 7ms or so. Pretty fast! This is just for experimental purposes now, just to see how fast I can go over the air. This will eventually change so that the client is doing all the work maintaining the DCC output while the master only sends packets that have changed since the last scan. This will keep the network traffic down.

Next step is to get the client going, decode the packet and apply it to the various things. Servos, Motor Controllers, lights, etc. With a controlwidget as a ‘decoder’ there is not much off limits- drive servos for steam locomotives or large motor controllers for battery locomotives. Or, a little more esoteric, create a ‘router’ that divides the mobile and accessory traffic into different xbee streams? On different channels too. Hmm.

I particularly want to try a sound decoder to see how that works, I wonder if I can use an HO sound decoder. Intercept the motor control data to drive a servo and then pass the data stream to the sound decoder? Hmm. Don’t know. Sounds like a fun experiment however…

dccdcc-input

Well, if you can’t beat em join em eh? Ha.

Since I’m putting together a new N scale layout, or at least I’m planning it out right now, I decided I should probably give DCC a go since it’s so popular. So I ordered an inexpensive DCC starter set, the MRC prodigy Express2. I am glad I did. Just on a test loop my little DCC switcher locomotive runs WAY better than it did on DC. And since I like the feel of the MRC Prodigy Express DCC controller (more or less), I figured, why not come up with a way to use that to control, via Xbee, for my G scale stuff too?

So after much scouring and searching via Google, I came up with an input and output circuit for my control widget board.

In the above picture you can see the DCC waveforms and the really simple input side of the circuit. I’ve also got my basic C framework built out and this looks like it will be a fun project if I can ever get the time to work on it!

Anyhow, the basic idea here is read the DCC out of the Prodigy output, transmit that via Xbee and decode it on the other end. Or pass it through, or both. That way you can use any DCC handheld you want to control battery powered locomotives or even live steam ones (via intercepts of DCC commands to servos and relays, etc)

So this should be neat if I can get it to work. Something new to learn anyhow, DCC as a message stream :)

I wired up my yellow critter with a control widget, a Turnigy 20A ESC and a 4.8v 2300mah nimh battery pack. Works quite well. I did have to add a relay to reverse the motor but that’s already supported by the software, it’s what I use in my RS3.

A pic from the video, out on the track at Gilbert Virginia.

Just can see the Xbee in the cab. The battery is in the engine compartment along with the Turnigy ESC. The relay to toggle the motor direction is also in the cab but you can’t see it from here.

The development platform for my Dash 9 whenever I get around to it. A close shot of the control board with the Xbee. This is the same control board in the Critter. There is just enough room (I think) in the critter to put in micro servos for the couplers but I have not gotten there yet…

And here is the critter with the handheld controller.