HO LED lighting

Over what DC voltage range do you operate your HO?  As you know, some HO engines will operate down to, say, 2V DC track voltage.  

What I consider the reference O-gauge LED circuit is the one from Hennings Trains shown on upper right.   The typical LM2596 module is about the size of the middle module.  The small DC-DC module on the left is the one you show based on the MP1584 regulator IC chip.  As you say, you would need a bridge to handle both DC polarities.  You would need a capacitor to handle anti-flicker.  Those components would be about the size shown but those are surface-mount which can be difficult to work with.  But of course they are available in wire-terminal form.  Note how your MP1584 module has extra pads on the inputs so could be a good way to mount the capacitor and bridge.  The MP1584 design is not suitable for AC O-gauge due to voltage limitations...but OK for DC HO.  So given the options presented, I'd go with the MP1584 module with an added bridge and cap.

I'm assuming you're driving individual warm-white LEDs … NOT a 12V LED strip?  

Thank you for responding. The engine operates nicely between 10 and 15 v.  I aslo noticed the extra holes in the MP1584 and thought that might work as you confirmed.  Indeed I was thinking about using strips, is that problematic ? Each car is 8 inches in length.

-Mike

Understood.  Well, the most common/popular LED strips operate off 12V DC.  Experience in O-gauge suggests between 10-11V DC is what they end up being set at for passenger cars.

Here's the thing.  A bridge rectifier between the DC track voltage and the regulator circuit drops the voltage by about 1.5V (two diode drops).  Then the regulator module itself imposes a voltage "tax" which can be around 2V.  So your 12V LED strip would be starved for voltage when the track voltage is low.  

Not to worry!  The 2nd most common LED strips operate off 5V DC.  These are also available in all colors (e.g., warm white).  Probably a bit more expensive per meter than the 12V style but prices are rapidly dropping after "someone" discovered 5V DC is everywhere there's a USB port.

Anyway, just search for "5V warm white LED strip".  They are available in the "standard" 60 LED per meter density.  So that would be maybe 10 or 11 LEDs in an 8" car.  With the 5V strips, you're not constrained to multiples of 3-LED sections either; in othe words the "cut-lines" are each LED rather than every 3rd LED.  In practice, based on the O-gauge experience, you'll probably find driving the 5V strip at somewhere between 4 to 4.5V DC will be appropriate for passenger car lighting.  That's where the adjustable output regulator module comes in.

I'm not familiar with the size of capacitor needed for anti-flicker in HO.  But I'd think something in the few hundreds of uF would be a good starting point.  10 cents.  Bridge rectifier, another 10 cents.  What are you waiting for!

I'm waiting for your pictures!   

Thanks Stan, your help is most appreciated. I'll certainly report on the progress.

-Mike

Note that if you choose to work with the tiny surface-mount components for the bridge and capacitor, GRJ has made a circuit-board that mates with the MP1584 converter.  Refer to following thread:

https://ogrforum.ogaugerr.com/...87#82100772862896887

It appears you still need to source the components and blank circuit board yourself (I don't think a kit with the board and all components is available).

Think I got the parts all ordered.  Plan to solder the generic bridge (KVP206) to the board and the 220uf cap to the extra holes on the otput side. Ordered 5m of warm 5v 3528 led strip.  Now we wait......

Note the cap goes on the input side.  Also, confirm you purchased caps with voltage rating of at least 25V (for HO DC) or 35V (for O gauge). 

I see the parts are indeed 10 cents a piece on eBay if you can wait a couple weeks for shipping from Asia...

Thanks Stan, I did order the 25v caps, didn't realize the caps needed to be on the input side. I found 4 suppliers in the US that said they have them, so I paid a little more , but excited to do this

Thanks again !

The first prototype , yeah !

Need to get some stranded 24 gauge or so wire , the 22 solid is too stiff.

Let there be light!