RGB Fader

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ParkingLotLust

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Ive seen plenty of schematics that show an RGB fader that fades automatically. What Im looking for, however, is one that lets you control the color based on a potentiometer (ie one way is all off, the other is all on). I was thinking of two ways to do this: a counter driving three transistors, one for each color; or a binary counter. How would I go about interfacing a pot into this, to let me control the color?
 
ParkingLotLust said:
What Im looking for, however, is one that lets you control the color based on a potentiometer (ie one way is all off, the other is all on).
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You can't put a pot in series with each LED, because the pot will smoke when its resistance is low when only a tiny portion of its resistive track will have a high current.
You could use a pot to control a transistor variable current source for each LED. Then you can adjust the pots to get any color you want.
 
I was thinking about that, but I thought it would be easier to throw an IC or two together (not easier to build, but easier to control in the end) and make a circuit that will fade all of them based on one pot (something along the lines of **broken link removed** but controllable, not automatic).
 
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That circuit doesn't fade all the colors at the same time. It just sequences the colors fading from one color to the next color and the pot adjusts how fast they sequence. The circuit is so simple that it gives only a few colors and always in the same sequence.

Three pots controlling transistor current sources will allow an RGB LED to produce about 64 million colors of your choice, one at a time. You can also adjust any color to any brightness within the LED ratings.
 
Im basically only looking to do what the circuit in the link does (mood lighting anyone) but to be able to control the colour on cue. 64 million colours is overkill for something like this, dont you think?
 
I have had my LED "mood lights" shining on the ceiling for years. They slowly and randomly fade between about 64 million colors and all brightnesses from very bright to off. They don't have an adjustment.
 
My "mood lights" have three fading circuits operating at very low slightly different frequencies. My circuit uses a capacitor and positive feedback to make the fading logarithmic like your vision's response to brightness, but other people say that this simple circuit works well:
 

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ParkingLotLust said:
Bowden's Fader fades one LED, how would I modify it to fade an RGB LED?
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An RGB LED has a red LED, a green LED and a blue LED inside. If you want all LEDs to fade separately then make 3 fading circuits like I said I did. If you make the timing resistor slightly different for each circuit then they will fade at different rates and the colors will randomly add to produce 64 million colors and all brightnesses.
 

I recently finish a similar project with the same base circuit. You really don't need to chang the timing resistor, the compent tolerences will give you slighlty different frequencies, which is a little better. Otherwise one color will tend to dominate. Also, I slowed it down by connecting two 220 uF capacitors back to back (neg together, positives goto pins 1 and 2 of your opamp) in place of the 22 uf. This was a suggestion from the origional circuit. You should go to his website, its well documented...
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I spent a lot of time trying to find an automatically fading/shifting RGB circuit, so your request kind of puzzles me. Basically, you want to set the LED to show just a single color, set with a trimpot. But I don't understand what you mean by fade in this case. You might put a seperate trimpot on each LED lead, three to choose the color, the one hooked up to the common would control the brightness. I'd have know way of even guessing how you would figure out and limit voltages and currents. The Blue and Green need about 3 volts, the Red is around 2 Volts...
 
An automatically fading/shifting RGB circuit can be found at **broken link removed** . What I mean by fading with a pot is the color changing when you turn it, fading into the next color (instead of just on/off). It doesnt have to fade, it was just an idea. The whole idea was just to have a single pot or control where if you rotated it all the way clockwise it would show a single colour with the LED and as you rotated counterclockwise it would fade to the next combination etc until you reached the most you could turn it.
 
The automatic fading circuit just changes 6 colors in sequence with the speed of the changes determined by the position of the pot.
Its 555 is missing an important resistor from DIS to RST (+). The 555 will probably smoke without the resistor.

You could change colors with a pot if the pot makes a variable DC voltage and is measured with an A to D converter. Then the digital bits drive the transistors that turn on the colors.
 
How would I get a pot to control a DC voltage? Just hook it up in series with a supply? Or would that just alter the current? Seems like this is going to become more difficult than I previously thought, but thats okay. I enjoy a challenge.
 
ParkingLotLust said:
How would I get a pot to control a DC voltage?
Click to expand...
A volume control controls the AC voltage of sounds.
A pot can control A DC voltage exactly the same:
 

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If you want real control over color, use a 3 channel PWM. A micro running a timed interrupt loop can manage the duty cycle of all three outputs. Basically, have 3 counts & counters that represent the duty cycle set points & on each interrupt increment all 3 counters. Then test each to its set point, if >: turn off that output. Every N interrupts constitutes the PWM cadence: turn on all outputs, reset all counters & do another cycle.

Pop up at each cycle end & check switches/pots/ADC (whatever) to alter duty cycle set points (color). Wrote one a couple years back that steps from one color to the next in a table at a settable transition rate. It alters the set points during transition every M PWM cycles, until next color achieved. A fun toy... <<<)))
 
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