Parts for GRJ's constant current LED board

A couple of comments. That cap should be fine but at 20mm height may cause problems fitting it into a tight spot. Have you looked at 680 or 820 uF sizes?

D1, U1 and L1 shud be fine.

R1 sets the upper output range. 27R gives you about 45 ma. Since you will be using at least 9 segments of leds per car you might want to use 24R which will give you 50 ma output. This may look better in streamliners, it’s all very subjective. I have settled on 24R for all builds these days.

R2 sets the lower output range and 200 ohms will give 5ma; 500 ohms will give 2.4 ma. IMO with 9 segments (27 leds) you will not likely want to be anywhere near there. I have never set a board output at anything less than 20 ma but that’s me. 500 ohm can’t hurt though.

Only my opinions of course, YMMV!

Rod

FWIW, in my commercial model, I went to 500 ohms for the pot, a number of people wanted lower intensity than they could get with the 200 ohm pot.  That probably shows up when doing stuff like a caboose, not sure when it's an issue.

@Rod Stewart posted:

A couple of comments. That cap should be fine but at 20mm height may cause problems fitting it into a tight spot. Have you looked at 680 or 820 uF sizes?

It is a bit tall, but I'll have room at the ends of the cars where I these boards can take up the whole height of the first level if they need to. There aren't many windows on the lower levels of these cars, so there's plenty of space for the board, even with a tall cap, at either end where I won't be adding any detail.

R1 sets the upper output range. 27R gives you about 45 ma. Since you will be using at least 9 segments of leds per car you might want to use 24R which will give you 50 ma output. This may look better in streamliners, it’s all very subjective. I have settled on 24R for all builds these days.

Thanks for this! I'll probably switch to 24R to go with the 500 ohm pot to give myself more range. That should help me get the brightness of each car matched even if some have more or fewer LEDs than others.