DCC in PBP

[boroko]

HI all,
I have been looking for a way to sent data over a two wire connection and have been stumped until I remembered that modern model railroad layouts use such a scheme to control their engines. Its called DCC.
http://www.nmra.com/standards/DCC/st...91-2004-07.pdf

They power the track with two pulse lengths of alternate polarity generated with an H bridge. There is an active DIY community, but everything I have found is in assembly. Has anyone done any of this in PBP?

I need the comm for other use, so the protocol is not as important as the coding and decoding on a PIC.

I'm going to try and get a fast enough PIC to use DT-ints for comm and still be able to get 8 channels of PWM.

Thanks for any thoughts
Bo

[skimask]

http://www.picbasic.co.uk/forum/showthread.php?t=4751
Putting DCC in the search field gets you a few results (I know, DCC is too short for the regular search)
Not a new idea though, putting an AC signal on a DC rider. I would think the hardest thing (if it's really that hard) is figuring out the hardware to superimpose this AC signal onto this DC carrier. Figure that out, and it would be just like sending serial data over 2 wires.

[boroko]

Thanks Skimask,
did the search and the only results were like mine: questions.
It seems that no one is interested.
I'll work on it and see if I can put it up. Seems like a powerful way to solve comm over two wires.

[skimask]

Well, what do you actually mean by sending data over 2 wires?
Do you mean just 2 wires or 2 wires that are already carrying power to another device?
I assume the 2nd...

[Charles Linquis]

I don't exactly know what you are trying to do, but a PIC with a USART can easily do comms and software PWM at the same time.

[Acetronics2]

Hi,

Here are some nice info ...

http://www.merg.org.uk/resources/dcc.htm

Assembler ... yess, but pretty well commented ! ... so you understand what's going on.

The "miniDCC" project also could be useful ...

Alain

[boroko]

Correct, send data over the only two connections available, that are also providing power.

To give this a bit of flesh, imagine addressing your Low Voltage Yard lighting. Two wires existing all over the yard. They normally are supplied with 12 vac. Insert a control box between the transformer and the yard wire that has a rectifier and H-bridge that reverse the lines at intervals of either 5 kHz or 8.5kHz. The receiver has a bridge rectifier and cap for storage of power and taps the raw lines to collect intelligence. On model trains, address, speed, accessory control, etc, are communicated. The commercial systems and the spec have a method for limited feedback by current (load) pulsing the line for simple acknowledgment.

Since my use is not for controlling trains, but instead, yard lighting and such, I need to be able to get into the code and tweak. The only examples of code that I have found are asm and as you can imagine, very dependent on cycle counts for correct timing. I'm not sure that I can handle that reliably. If someone had already done it in PBP, I could look at and get some ideas. I'm pulling apart the .asm code now and trying to get my arms around it so that I can do it a bit easier. I may be able to leave the message collection in .asm, and just write around it, but first I have to get the interspersed (and carefully timed) "train" stuff out of it and get the pulse measurement and word collection back working.

My app uses Darrel's DT-ints to generate 8 channels of PWM. To mix that with watching for, and decoding 100us and 200us pulses is a lot. My path is to separate them on different PICS until I can get it working. Once that is running, I will look at a faster PIC or moving up the food chain.


Hope that gives everyone a better idea of what I'm trying to do. Looks like my chance to figure this out and have something to contribute.

Thanks
Bo

[mackrackit]

Sounds like a low voltage X10?

Here is some info.
http://davehouston.net/