Adding LED lights to a PS2 Engine

gunrunnerjohn posted:

Yes, the resistor is in the bulb.  If you want to use a bare LED with PS/2, a 220 ohm resistor in series is the ticket.  Since the lights are driven with PWM DC voltage, you don't need a diode, the voltage never goes negative.

John, I have a ps2, 3v loco. Where can I get the bulbs with built in resistor?

Joe Gozzo

I have no idea, most of the bulbs with resistors have much higher value resistors.  If you're soldering up the rig anyway, just use bare LED bulbs and 1/4w 220 ohm resistors.

I've been using 3V warm white, 3mm LEDs with 1/4 watt, 560 ohm resistors. To me they look closer to incandescent bulbs. 220 ohm resistors make the LED too bright, at least to my eyes. So if 220 ohm is to bright to your eyes 480 or 560 ohm resistors are another option as well. 

Old, old add, when Train America Studios was around.  Bi-color LED's that change color when the engine direction is reversed.  I've had some luck with LED's, a similar two diode hook-up, and 1000 ohm resistors hooked to track power.  

Both the Ditch lights and marker lights have been added. 

I use amber LED's with my 220 ohm resistors.  FWIW, I want the headlights to be bright, unless you're hearkening back to the old lamps on 1800's steamers, locomotive headlights are pretty bright.  When I have markers and class lights, I typically try to tone them down with larger resistors, in the 2200-4700 range.

gunrunnerjohn posted:

PWM-Pulse Width Modulation

The effective voltage is 6VDC, but it's a PWM signal.  The voltage varies from 0V to a higher value, in the case of the PS/2 boards, that's around 20-22 volts max.  So, the duty cycle would be around 25-30% for an effective voltage of 6V to the bulbs.

They use PWM for the lighting circuits?!  Why on Earth did they do that? Do they vary the duty cycle WRT input voltage?

Why not just regulate to a steady DC voltage? I'm sure the CPU/DSP/ASIC on there would need a steady voltage, right?

Quite simply, it's much easier and more efficient to use PWM.  Also, you can very easily digitally dim the lights if desired.  I use PWM for the lights on my Super-Chuffer, as well as for the smoke fan voltage.

gunrunnerjohn posted:

Quite simply, it's much easier and more efficient to use PWM.  Also, you can very easily digitally dim the lights if desired.  I use PWM for the lights on my Super-Chuffer, as well as for the smoke fan voltage.

Any particular PWM that you use??

gunrunnerjohn posted:

I use amber LED's with my 220 ohm resistors.  FWIW, I want the headlights to be bright, unless you're hearkening back to the old lamps on 1800's steamers, locomotive headlights are pretty bright.  When I have markers and class lights, I typically try to tone them down with larger resistors, in the 2200-4700 range.

Well the 220 ohm resistor makes sense with the amber LED. I tried the lower ohm resistor with warm white LEDs and it was far too bright for my taste. Blindingly bright.  

I’m with John. I buy the ultra bright for headlights. I wanna see a spot on the walls. 

Neat thing is different ohm resistors can be used, so the OP or anyone else can get the effect that they want. No wrong way here. 

Woodson posted:

gunrunnerjohn posted:

Quite simply, it's much easier and more efficient to use PWM.  Also, you can very easily digitally dim the lights if desired.  I use PWM for the lights on my Super-Chuffer, as well as for the smoke fan voltage.

Any particular PWM that you use??

Particular PWM?  I use around 2khz for the PWM rate if that's what you're asking.