Led fader circuit to run multiple leds

im trying to make a led fader that will run 8-10 white leds, and then when a switch is turned on, it will fade the same number of amber leds ON and the white ones OFF simultaneously,, how can i do this?

Well, you could use a DPST and 2 identical circuits, one for the amber and 1 for the white LEDs, a simple capacitor circuit should work, you should experiment with capacitors to see which one fits your needs, then get the same exact components again to build a second circuit. Hook each of the + lines to the different rails on the DPST switch, and presto you have a circuit.

Someone else on here should be able to provide you with a LED fader circuit, which I am guessing is going to be a VERY SIMPLE capacitor, wire, and battery type fader.

**broken link removed**

The second circuit cross-fades, as you requested...

that looks really cool, but will it run more than 2 leds? thats the problem im running into, i dont know how to multiply the resistances and power needed,, which parts id need to substitute for bigger ones to run more leds.

parker30120 said:

that looks really cool, but will it run more than 2 leds? thats the problem im running into, i dont know how to multiply the resistances and power needed,, which parts id need to substitute for bigger ones to run more leds.

Click to expand...

There is a pretty detailed description of the circuit, kind of why I posted the link.

Blue LEDs are around 3.4 volts, so from the 9 volt source you can only use 2 in series, like in the schematic. Just add more transistors until you reach the number you want.

Amber is around 2.2 volts, so you could put 4 in series for each transistor.

**broken link removed** can help you pick the best resistor to put in series with the LEDs. 100 ohms is probably to high for 4 amber.

The opamp isn't too critical, if you got something on hand, most likely it will work. If you need to buy, might as well stick to the 324 (cheap), and you don't have to re-assign pins...

This is the simplest circuit to cross-fade that I've seen.

thank you for your help its much appreciated

The Fading Red Eyes circuit uses two 1.8V red LEDs in series that have a total voltage of 3.6V. If you use two 3.4V blue LEDs that need 6.8V then they will not even light since the ramp's voltage is much lower. use a single blue LED.

The transistors can each drive about 5 strings of LEDs/resistors. Then the transistors will be a little warm.
If each little transistor drives 10 strings then it will be too hot.

Power transistors like the TIP31 and TIP32 will each be able to drive 10 strings of LEDs/resistors.

I want to use something like this to drive leds in the style of the interactive led table.
I have the motion sensor circuit but I don't know how to set up multiple strings of leds.
On the evilmadscientist site they have 24 leds with 15v+at the top and 15v-at the bottom and the signal wire in the middle.
My leds are white and require 3volts to run and my power supply is 9v and my signal wire from my motion detector circuit seems to supply about 3v.
Obviously I can run 3 leds at 3v on 9v supply. If I run 4 leds at 3v each with the signal wire connected between the 2nd and 4th led this should work but all leds are very dull.
Any help appreciated.

You cannot power three 3V LEDs properly from only 9V. Two extra volts are needed for the current-limiting resistor. So the supply must be 11V or two 3V LEDs can use a 9V supply.

If the 9V supply is a little 9V battery then its voltage will quickly drop to only 7.2v the drop slower to 6V.

Multiple leds on one supply

Thanks audioguru for your help.

What I want to do is run many leds from one supply eg a motion sensor circuit.

Do I just connect the 12 volt line to one current limiting resistor to the pos of an led and the neg to a collector of a transistor.
The emiter to -12 volt and the signal from the motion detector to the base.
Do I need one transistor and current limiting resistor per led.

I have seen arrays of leds with the signal wire in the middle of the array.
How does that work? Does the signal raise the overall voltage of all leds to allow them to work.

So on 12 volts, I connect the signal wire with 2 above and 2 below and this should work.

The answer is probably very simple but I cannot get this to work on my wishboard.

If the motion detector gives a fairly high current then the base of the transistor should have a series current-limiting resistor.
With a 12v supply then five 2V red LEDs can be connected in series and in series with a current-limiting resistor and driven from one transistor.
Three 3.5V blue or white LEDs can be in series.
I don't know how many transistors the motion detector can drive since it doesn't have a datasheet nor a schematic..