MTH diesel lighting question

Buy the ngineering.com MARS Light Simulator.  Use that to drive the LED.  you'll also need to insert a little regulator to filter the PWM voltage into something the simulator can use.  A 100 ohm resistor, a 100uf cap, and a TO-92 three-terminal 12V regulator would do the trick.  The resistor is just there to prevent a big capacitive load to the lighting FET, not sure if it would be happy with that.

PS2 engine? or PS3?

Some soundsets have the mars like effect built in. If you have the test stand you could see if they are active?

So you could drive your lower headlights with the mars circuit in the PS2 instructions.

It looks like it's the 8 pin harness so I'd use LEDs with resistors for PS2 (or straight with PS3 from the 40 pin).

Sorry, Chuck. I'd guess that you already know all this so I'm not sure what you are asking?

Joe, it is a PS2 engine. There is no ditch light function programmed as this model has no ditch lights to feed off of. I could use a SP SD40T-2 soundset and rearrange the bulbs, but no rear numberboard lights in that set. I like the sound programmed in, so don't want to change that. I'll check into John's suggestion. Thanks.

Here's what you need.  In your case, since you are looking at the PS/2 headlight, swap the diode for the 100 ohm resistor.  The PV (purple) lead goes to the plus side here.

Do not be fooled with the 10V minimum input, the PWM peaks at 20-22 volts and will drive this circuit fine.

Hi John, All four front headlights are powered from the same 2 pin connection. What I would like to do is use the 6 volt power from the lower headlights and use that to provide power to a Mars light simulator. Any circuits that can use 6 volts to operate in your bag of electrical tricks? Of better off with ngineering kit?

Chuck, the lights are actually PWM driven, so you'd have to have a circuit to give you pure DC.  Once you have that, the thing I use is the MARS simulator board, I can't do a better or cheaper one.  I did a MARS simulator that looked very similar to the ngineering.com one on an Arduino a long time ago, but it's really not nearly as practical as the MARS simulator.

Thanks for your insights John.

Actually this is a generally useful idea for PS2.  That is, how to convert the PWM (pulsating) light output to a smooth DC voltage suitable for powering a specialized lighting module that requires DC voltage:

Above photo modified from a recent thread.  Some of the component values are different but the hookup is the same.  Less than $1 in components - but if your cupboard is bare you'll get dinged for minimum quantities and shipping.  The key is to observe that the 2-wires from a PS2 lighting output has polarity.  The "+" side is the so-called "PV" signal (from pin-2 of the 12-pin PS2 board) and is readily found as a wire-nut with lots of connections as its shared with each lighting and coupler output.

Stan, since the PV is always positive in respect to the switched lighting output, do you really think you need the diode?  I tend to stick a small resistor there, just to minimize any inrush when starting up and charging the cap.

I've used the resistor, cap, and regulator a few times for the MARS light on PS/2, it's always worked out fine.

For 1-cent, I think it's cheap insurance against installing it backwards...albeit a one-and-done affair...who wants an exploding cap...or a damaged, tedious-to-replace light FET on the PS2 board?  In general, the diode-cap-regulator "circuit" could be used to provide a small amount of DC power if hooked direct to AC track voltage maintaining common-chassis-ground.

No argument over limiting inrush current, though I hasten to ask if you've measured the off-resistance of an MTH 6V bulb (and Chuck apparently has 4 of them in parallel).  I'll bet you can count the Ohms with the fingers on one hand!  I wonder if the light FET would be happier turning "on" a 100uF cap or 4 parallel cold filaments?!

Anyone looking for a first-time OSH Park project to design a small printed circuit board might consider something like this.

That ship has kinda' sailed Stan, I did this one a few years ago!   It's actually the board I use to power the MARS simulator when I use them in the MTH application.  It also works for Lionel lights, you just have to remember the light outputs are negative in respect to ground.

This has the DCS choke, but you can just jumper that.  You also don't necessarily need the 1uf cap, that's only the regulator for stability.

Nice!

So all you need is Chuck's address to mail him one...