I need help finding a post that showed how to build a resistor test box for LEDs. I did a search and couldn't find it. Also, I'm not sure it was on this forum, but I hope the collective forums brain power can help me find it. The post I'm looking for is NOT Peteski's "Build your own (cheap) LED tester" or DKS' "LED/Small Motor Tester/Evaluator" The one I'm looking for used a rotary switch connected to various resistors in a project box with Radio Shack binding posts to connect power and LEDs. The writer also posted two home drawings of resistors values to use around the rotary switch as well as a wiring schematic. Does anyone the discussion I looking for? Allegheny
I don't recall the post, but why not use a potentiometer? When you find the level of illumination you like, you measure the pot with an ohmmeter and buy the closest resistor value. Or buy several pots if you're wanting to test and match the level of illumination across several colors. Something like a 5K pot (or 10K) would work. A precision pot like this one with ten turns would be just the ticket for exactness. There are twenty five fixed resistor values between say 500 Ohms and 5000 Ohms, so anything using a rotary selector is going to limit your work. After a lot of messing around, I ended up using 1000 Ohm for my Green and Yellow LEDs and 4700 Ohm for my Red LEDs, all with a 12VDC power supply. The level of illumination isn't perfectly uniform across all three colors, but it's close. I also used some special colors for special operational functions and these were Blue and Orange (used 43K Ohm on both) and Pure Green (used 150K Ohm), so greater values might be needed on your railroad too. We have members here who know a whole lot more than I do about these things and they will likely have better ideas.
I should have added a caution. You'll want to buy a 750 or 820 Ohm resistor (these are stock values) and solder it to the center tab on the pot and keep it there, wired in series as you test for the level of illumination you like. Without this resistor, you could wind the pot down to 0 Ohms and instantly burn out your LED.
