Diagnosis of LED Lighting Circuit

try putting a .1 uf NP capacitor on the output.

Dale H

What value is R1 in your circuit?  You are only lighting 12 LED's in four groups, I suspect your other cars had more LED groups and thus each LED was dimmer.

If "much brighter" then your regulator is not regulating.  Double check that your LED strip(s) are indeed connected to the ADJ pin of the LM317 and not to the OUT pin. 

Measure the voltage across R1.  If in regulation you should measure about 1.25 Volts DC.

Is the hum coming from the car?  If so, where?

If you have 9 LEDs connected in series, what is the input voltage from

the regulator? Each group of 3 LEDs require 12V so 3 groups of 3 would

require 36V.  

The humming was caused by my test track which still has a black coating on the 3rd rail. On my layout, the humming does not occur. However the brightness of the LEDs is too much, so I am thinking about changing the value of R1.

R1 is currently 100 ohms. I tried 270 ohms, but the LEDs are still too bright, and they look brighter than with R1 = 100 ohms.

Could it be the that the regulator has a lower current output with less resistance? I am going to try 68 ohms just to see what the difference is.

If you want to dim them, you have to increase the value of R1.

Here's a page on constant current with the LM317: Constant Current with the LM317.

If you're getting brighter lights with higher value resistors, something is either wired wrong or broken.

I found my mistake. In my endeavor to make the volume of the assembled components as small as possible, I accidentally wired the LED strip to the output of the regulator bypassing R1. Yesterday I fixed the cars with bright lights and all is well.

I discovered my mistake by changing R1, and it made no difference.

Here some pictures of my best efforts to date:

My soldering skills are improving, but my eyesight isn't!

This a Rail King 54-foot combine converted to LED lighting with the above circuit package.

A learning experience.