So I got a great ebay deal on bright white leds and 1000 ohm resistors. Does increasing the resistance increase or decrease the brightness? What about voltage changes? Thank you
The LED is a current device. The more resistance the dimmer the LED. A white LED operating voltage is a bit over 3 volts for max brightness, 20ma max.A typical white LED will draw about 10ma at 12 volts with a 1000Ω resistor in series with it. Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
Larger the resistor value, the less current. The less current, the dimmer the LED.
If they are too bright for your use with the 1000 ohm resistor, try 2 of them in series. That makes a 2000 ohm resistor. If that works, you cna buy 2.2k resistors and use just one. If it's still too bright, try a third, or fourth even. Once you have your desired brightness, add up how many resistors you put in series, and then order the closest standard value - resistors don't go up by 1 ohm increments, or even 10 ohm increments, when you get to 1K and greater. So pick the closest available ones to the sum of your test.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Having worked in electronics for many yers, I just take a 5K pot out of the junk box and set it at max resistance and with an amp meter set to ma, put it in series with the LED and 12 vots DC, adjust the pot until I get the brighness I like. Then I read the pot resistance with the meter. Very simple. Record the ma reading. Pick a resistor close to the reading. Not a big deal. I use two meters.
When you pull the shell on a DCC loco you should have some knowledge of basic electronics. This is all on the Internet. Google should be your best friend.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
If you don't mind having one more gadget around and you have a little extra allowance in your pocket, a decade box can be a helpful tool.
Good Luck, Ed
Yes. I eventually made one when I retired.
Just be careful using a potentiometer by itself, if you turn it down too far to start, you will have a one time flashbulb simulator, after which you will have created a DED - dark emitting diode. It's all fine if you are careful - same with an ordinary decade box. For LED testing, it may be best to make something a bit more complex, that has a minimum resistence no matter what you do that results in the LED not getting more than the maximum current, and reduces it from there - measure the total once dialed in to your desired brightness and use that as the fixed resistence for the final installation. For 12 volts and most LEDs - the would be say a 470 ohm resistor in series with the 5K pot. Thus at minimum on the pot, the LED would still be limited to about 19ma. Graduallty turn the pot up and the LED will dim. When you have it like you want, the resistor to use in the final circuit will be 470 ohms plus whatever measures across the pot. Or just measure across both for the total. If you put both the fixed resistor and the pot int he positive side of the circuit, measure ohms from the plus input to the plus LED terminal, whhich is then the same as measuring across the fixed resistor plus whatever the potentiometer is set at.
Actually there is a slick board on eBay for building a decade box. All the hard work is already done, just wire up the switches. https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313&_nkw=1R+-+9999999R+Seven+Decade+Programmable+Resistor+Board+Step+1R+1%25+1%2F2+Watt&_sacat=0This is the one I built.The mini round female header strips fit the male pins on the board, solder plug and go.Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.
Your faceplate probably cost more than the resistor board And if you shop carfully, you cvan save 3 cents! There one for $3.15, most of them are listed at $3.18.
If I didn't already have one (which I don;t use, it just takes up space on my bench - one nice thing is it's made up of 1 watt resistors, not 1/2 or 1/4), I might put something like that together. Perhaps if I did more analog stuff... but all my projects are digital, so the resistors are simply for current limiting and easily calculated. If they were uses as part of the frequency of an oscillator, or in an RC filter, where picking the right value is as much an art as science, having the ability to swap values without replacing parts would be very handy.
The knobs cost more than the board. I figure I have about $23 in it, the switches were $1.25 the housing was $8.36. The switches came with knobs but didn't like them.The front panel is .03” clear Styrene with Mel printed text behind it. It was kinda a neat project, a few hour break from train stuff and I needed one.Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California I'm beginning to realize that aging is not for wimps.