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My Digitrax Zephyr has a jump port with 3 connections, 2 for two cabs and 1 for common.

For those who don't know, the jump port allows you to connect up regular controllers as additional throttle inputs to the DCC command station.

My question is can I hook it up to my MRC280 dual controller? This is a standard type of controller with dual speed controls. This has 4 connections, two for each speed control. So is it safe to short two of them together to make a common for the Zephyr's jump port


This would imply that the two speed control circuits inside the MRC280 are completely isolated and come from separate transformer windings. Is this the common practice? I can't find anywhere in the instructions that it is safe to short two of the outputs together but I guess this is what people would do if they are wiring a layout dual cab common return
 

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I've done this with two Gaugemaster handheld controllers, it worked but not as well as I'd hoped - the best description of it was like going back to 14 speed steps, and I got top speed with the throttle only 1/4 way round. Much better to use another Digitrax throttle in the Loconet port.
 

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I'm slightly disappointed to hear of your Gaugemaster experience.

I have been planning to take the plunge with DCC with a Digitrax Zephyr - I was a attracted to the jump inputs coz I don't want to buy a second throttle straightaway, but we want two-person control. I have a rheostatic controller - it may be old but it works well. This is presumably the sort of device Digitrax mean by a "smooth dc controller", but I haven't been able to find much about this on the 'net.

Does anyone know if the specs of the jump inputs are available somewhere?

Rick
 

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QUOTE (rickb @ 6 Nov 2006, 21:06) <{POST_SNAPBACK}>I'm slightly disappointed to hear of your Gaugemaster experience.

I have a rheostatic controller - it may be old but it works well. This is presumably the sort of device Digitrax mean by a "smooth dc controller", but I haven't been able to find much about this on the 'net.

Does anyone know if the specs of the jump inputs are available somewhere?

Rick

With respect a "rheostatic" controller is not really what Digitrax probably meant. Eith that or it may just be a compatablility issue between digital & analogue device's.

Probably a case of "suck it & see".

best regards
Brian
 

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Sorry for not understanding your reply. I can't think of a smoother smooth DC than you get with a rheostat - provided it's feeding from a smoothed power supply, of course.

Does anyone know what range of inputs is expected for the jump terminals? e.g. 0V to +/-12V, or 0mA to +/-200mA perhaps.

R.
 

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QUOTE (rickb @ 7 Nov 2006, 18:35) <{POST_SNAPBACK}>Sorry for not understanding your reply. I can't think of a smoother smooth DC than you get with a rheostat - provided it's feeding from a smoothed power supply, of course.

Does anyone know what range of inputs is expected for the jump terminals? e.g. 0V to +/-12V, or 0mA to +/-200mA perhaps.

R.

Agreed regarding the smoothed power supply, but with no or very little load you will get almost the same voltage out as in on the first setting with a rheostat controller. The just could be where the problem lies.
best regards
Brian
 

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QUOTE (rickb @ 7 Nov 2006, 18:35) <{POST_SNAPBACK}>Sorry for not understanding your reply. I can't think of a smoother smooth DC than you get with a rheostat - provided it's feeding from a smoothed power supply, of course.

Does anyone know what range of inputs is expected for the jump terminals? e.g. 0V to +/-12V, or 0mA to +/-200mA perhaps.

R.

A "rheostat controller" to me implies an ancient piece of kit that only produces any kind of control when connected to a load such as a locomotive.

I would try turning the control up to maximum and then wiring a 10K potentiometer across it with the controller outputs across the track of the pot and the pot slider connected to the jump port. You'll also nee a common connection from one side of the controller.

Andrew
 

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Thanks for this. I took the top off my old H&M controller and worked out the way it's wired up. It has a 45ohm flat wirewound track and wiper, and also a concentric ring for reversing the direction of travel, depending on whether it's rotated clockwise or anti-clockwise. Simple and effective at feeding variable current to a loco motor.

What the Zephyr jump input needs (*) is a variable voltage, reversable in sign. Assuming the Zephyr full range is +/- 6V, then the old controller could possibly be used as a potentiometer, but only by wiring the 45ohms directly across 6V. This would be far from ideal because 130mA current would run through the wirewound track continuously. If I put a series resistor of perhaps 520 ohms, the current would fall more than tenfold - but so would the voltage.

So I'll have a think about wiring it via a simple amplifier consisting of a transistor or op amp, so that a more modest current flows through it but I can set the output voltage range. This isn't as easy as I'd hoped.

Maybe a simple potentiometer in a plastic box and with a reversing switch will have to do instead.

Rick

* PS I don't know the specs of the jump port yet (Digitrax haven't yet responded to my request for more info) but Tony's Trains has a useful article by Don Fiehmann: http://www.tonystrains.com/technews/zephyr-cab.htm
Don's article mentions the input impedance of about 1kohm and the input range of +/- 6V can be deduced from his circuit.
 

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Theres two problems with using your average dual controller as jump throttles on the Zephyr.
First, most controllers go way over 16V with no load and the Zephyrs jump port don't represent much of a load at all (1k), that's why your train goes full speed before you're a quarter of the way round.
Second, most controllers supply rectified but unfiltered DC which looks like this:

I don't know if the Zephyr's jump inputs would filter this or not.

Ok three problems :^)
Third, if the dual controller uses a single transformer there may be a problem connecting two of their outputs together as commons unless the controller is designed for common return.

Don Fiehmann's circuit is designed to output +/-12V (8V AC rectified and filtered comes out at approx 12V). It's a nice, neat design, though :^) I envisioned something controlled by a garage door opener for mine but I haven't thought any further about it.

The simplest and safest DIY jump throttle would ideally use a 12V regulator and some kind of emitter follower circuit like this one from Talking Electronics:Simple Throttle, only you wouldn't need such a big heatsink or rectifier.

oh and Hello! :^)
 
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