If ...

"beamendsltd" wrote

You on the whisky as well? If so, enjoy! ;-)

John.

Trinary has been around for a while - one of those things that *ought* to be useful, but...

This link gives a starting point....

Richard

Gets a bit existential there "The smallest number corresponds to logical falsity, the highest number to logical truth, and the middle value to logical neutrality (neither truth nor falsity)"

Is the middle value one of those things that cannot be defined - it just is. cos are you allowed to define something by describing what it isnt.

Cheers, Simon

Err, I guess tri-state. Elektor Electronics is a Dutch language magazine, translated into English, but they did say "trinary".

That seems fair enough: 0 volts / above 0 volts to less than max volts / max volts.

It's too high to be zero and not high enough to be 1.

In this case, yes, because it's defined as "not less than but not as much as".

Regards, Greg.P.

In message , Greg Procter writes

What's wrong with "ternary"

You could use tri-state but you would need extra circuitry to force and hold the line to a third valid state when the transmitter is tri- state. The garage door opener chips that have been discussed used three voltage levels. In a 5V logic system you would use 0V, 2.5V, 5V nominal.

MBQ

Two or four wires are still a cable! Lester is talking about the difference between a cable and using the rail/wheel interface to make the connection.

If you are propsing to replace DCC to locos with CAN (or ethernet is another one I've seen proposed) then you are onto a loser. The environment is simply too noisy and error prone.

If you are propsing CAN as a layout control bus then it has already been done by Zimo.

MBQ

Is that allowed in public???

That is the one :) Neither CAN or Ethernet can carry POWER on the same pair as is used for the data, which is the whole point of DCC

And given the price of USB modules, THAT would be fine for the hard wired control loop!

The bit of the jigsaw I'm not understanding yet is the return path from the locos on the track to the DCC controller. If you stop sending power for a period of time will we not have less power available at the loco? I'm personally thinking Gauge1 here where I need to get a power a long distance, and I can't see how the decoder can drive it's reply message back without having a powerful driver as well?

Not a problem - you just raise the voltage to compensate.

Build a smaller layout! But seriously, there are limits. In particular you would need large enough DCC bus wires to keep the track voltage up. I also understand that there can be a problem on really long circuits where the DCC signal can become sufficiently out of phase around a circuit to cause control problems. G garden layout control generally uses 24 volts and large layout owners don't bother with DCC. They go to on-board batteries for power and radio control. My garden railway will initially extend about 240m and I won't expect to get by without serious voltage drop.

But you have a nice piece of metal as a separate third earth wire and +13 or so volts on another. ;)

Two cables - two rails! CAN can (ha ha ha!) cope with noise - you should see what goes on in car (I was feature owner for CAN on the "Medium Sized Bentley").

Richard

Not the sort of errors you will get from intermittent contact between rails, wheels and pickups. At least not at any useful data rate.

MBQ

That's an urban myth. You can get noise problems and fitting an RC in series across the tracks will usually them. It has nothing, however, to do with phase mismatch, transmission line theory or termination.

MBQ

I suspect that's why it's never caught on - only six people understand it, and they live on a different planet to the rest of us...... :-) I had an hours lecture about it, and it was one of those things that while the bloke was talking you think "Wow, this is great stuff!", but 10 min later you wonder just what the hell he was on about!

Richard

OK, I stand corrected.

The following applies to Railcomm, I don't know how Digitrax transponding works.

The power is cut for only 2 (can't remember the exact number) during the preamble between packets. It's less than 10% of the total time, even with the shortest packets so you will see a slight drop in the power to the loco. You rely on inertia to keep the loco moving. The rails are shorted together during the cutout.

The decoder has a small capacitor to keep it alive during the power outage and transmits a few bytes 250kbits/s by injecting a current into the rails (which now form a complete circuit). The detector is in series with the feed to one rail and detects the current flow.

The NNMRA RPs (9.3.x) are here

There were experiments to ac couple a 4MHz carrier from the decoder onto the tracks but they were not followed up by the NMRA. This wouldn't require a power cutout but I think there were issues with EMC and detector complexity.

MBQ

The off period is several milli-seconds whereas human eyesight can detect anomolies of the order of 1/25th of a second.