PS-2 Conversion Question

https://ogrforum.com/topic/mux-board

simply stated, this board-pair controls two lights over one tether wire.  relatively simple circuit in the realm of DIY if you want to save a few bucks.

Rod,  The only other way to have a controlled circuit would be to run a single black wire along the tether with a disconnect and pin it into the Interior connector of the 12 pin and then use it as one of the legs to the interior bulb connector.  Purple PV is the other wire inside the engine to power the cab light.  Normally in a MUX engine this could be a double bulb for CAB and firebox glow.  G

With independent outputs from the PS/2 electronics in the tender, it would be pretty easy to send up multiple controls to the locomotive.

If you wanted to eliminate the extra wire, here's a thought.  Just spit-balling here.

Let's assume we have front markers, headlight, cab lights, and perhaps firebox flicker as separate signals in the tender.  We'd like to have these transmitted to the locomotive.

Lift the headlight from the tether and use it as your communications line to the locomotive.  Encode a simple serial word that is continuously transmitted that would transmit zero for off and one for on for each of the discrete inputs.  Being lazy, I'd probably do this with one of the little Arduino boards, no hardware to build!

At the receiving end, you'd just use a UART with a parallel output to decode the stream and provide continuous outputs to feed the individual functions in the locomotive.  The locomotive board would just use track power to generate the output signal.

John;

Interesting idea, but a little beyond my skillset.

GGG; simple enough to do, and not a big inconvenience as long as you are not frequently moving the engine on and off the layout.

In the previous thread a suggestion was made to use the front coupler circuit, but according to the upgrade manual, you have to give up headlight control and use that wire for the coupler circuit if desired.

I can't really see any other circuits in the 10 pin tether that would be readily available without giving up another feature.

One possibility is to add power rollers on the tender and free up the power wire in the tether. This may work OK and only requires the addition of a couple of rollers. Anyone see why that would not work? Some PS-2 engines I have seen actually use rollers both on the engine and tender, for redundancy I guess.

Maybe the ground wire in the tether is another possibility?

Rod

I would NOT ever disconnect the ground wire between the two pieces, in a derailment you could have power on one of the frames and swiftly cook the electronics!  The power is a possible candidate, though I think I'd be somewhat reluctant to do that either.

I looked over the 10 pins and couldn't figure out an easy way to free up a wire.  I suspect MTH couldn't either, which is why the oddball lashup with the two diodes for the common in the locomotive.

I'll have to give some more thought to my solution, as it would expand to more than one additional control.

John;

Agreed on the ground. I had not considered that.

Keep us posted on your thoughts about your solution. You are kind of our go-to guy when it comes to complicated electronics.

Rod

You are kind of our go-to guy when it comes to complicated electronics.

That's a scary thought!   You sure you want to go out on that limb?

You can get micro-mini plug/socket sets, up to 4 conductors with very fine wires (adequate for cab lighting, & have a second tether".  I used them when upgrading a tiny Weaver 0-6-0.

You can, but it's a pain to have multiple tethers between the units, bad enough we need one.

Rod, the single wire with disconnect is an easy eloquent solution.  The use of a front coupler is on those engines where the limitation of a ten pin connector don't exsist.  Shay for example with a 16 pin harness and the wiring inplace without the coupler.

John, Why the concern about the chassis ground?  The chassis ground is not a protective ground.  It is part of the AC input to the 7 pin.  Plus you have a chassis connection via the drawbar.  I do think you risk continuity of power to the board as the engine moves along via axle wipers and wheels.  The upgrade kit does have the wire with terminal to ground to the tender frame.

The tender rollers would be on a short wheel base so you may wind up with issues on the switches if you eliminate the center rail wire.  MTH has at least one engine were they removed the center rollers on the engine because they needed one additional wire for control.  Board was in tender and used tender pickups.  So both may work fine depending on how well the tender is grounded or powered to the track.  G

I think the power is not as much of an issue, I guess I just get "spooked" when a common ground is not maintained.  I know that I'm not interested in sending logic signals across without ground.

This may be more of an issue with TMCC as the logic signals are indeed returned to frame ground, and the scenario I mentioned would certainly put the electronics at risk.  With all the cautions about not grounding lines from the PS/2 package, I just figure that having a consistent ground can't be a bad thing.

I've seen the MTH stuff both ways, with rollers just on the locomotive, and rollers just on the tender.  Again, I'm not as worried about the power, and if I were going to steal a signal line, that would probably be a candidate.

As you say, another consideration is getting a good ground on the tender as you don't have the extra contact of the locomotive wheels.

Perhaps I've just designed too much aerospace stuff, they'd turn over in their grave if I suggested such an arrangement.

John, Understand.  Yes MTH took a different path.  AC and ACG come in to the seven pin (red and black) and power the FWB Rectifier and a pair of diodes.  Everything else is run on the DC side of those components.  Normally the blue is PCB Ground or Printed Circuit Board ground.  The tach, volume control, and smoke control all use this as a reference.  Also all the FETs dump to the PCB Ground.

Having the DC Positive Voltage (Purple) or the output of the controlled items get to AC Chassis ground is what causes all the problems with the electronics.

So it really is a continuity of input power issue.

I still think you need to design an electronic toggle switch that allows a CV 6VDC to be applied to more then one item with return to the PCB ground in the engine based on how many times the headlight is cycled off and on.

Once enables cab light and firebox glow, twice disables cablight but leaves fire box glow on, third disables both, fourth enables cablight only.  Or some equivelent sequence.  :-)  G

I figure that I'd use a uP in the tender so I could have some flexibility on the timing or indeed what inputs did what.  Something silly like turning on the ditch lights would enable the encoding instead of the normal function of the headlight, then turning them back off would restore normal function.