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RGB Potentiometer help!
Hey guys and girls, I've got a question! I've got 3 voltage regulators set up in parallel, wired to output 3.27V @ an amperage that I don't know (for some reason I can't get a reading on my e-meter) Anyway, The outputs from those 3 regulators are going to 3 pots, which in turn go to a set of 3 LEDs, 9 in total (3R 3G and 3B). My problem is that those pots have a max resistance of 2k ohms, and that the LEDs aren't shutting off when the resistance is maxed out. Can you guys find a way to make the LEDs shut off, yet still go on at full blast when the Pots are open? Thanks, -Josh
Discussions
10 years ago
For a dimming a led you need work with PWM pulse width modulation, non for voltage variation, in a few days a i gonna make an instructable and get you a pcb for a dimming control using an le555, now i need to find a mosfet that works fine, other thing that you need yo think if you gonna make you one is you gona need a npn transistor for sitching the mosfet that work about 190 mhz for fast and good switching dimming. the led is not a inductance light , the led works with ions . don´t waste your money, varing the voltage you can the led in 10 percent 30 percent and 100 percent , read about pwm. or wait my pcb is very cheap.
11 years ago
. Not sure I understand, but try using a "larger" pot. I'll guess that 47K would be easy to find and work well enough to tell if that's the problem. If 47K is too sensitive, try something a little smaller until it feels right.
Reply 11 years ago
The thing is, I want the ratio between the resistance and the power output of the LED to be almost direct, not exponential. I'm going to draw up a schematic, but even with the 2k pot, the LED just suddenly clamps within the last 10 degrees of the pot's rotation. This isn't what I want. I think I might have the wrong set-up. I think my pots are in the wrong place, according to Dan's schematics for his RGB high-powered lamp, that is.
Reply 11 years ago
. If you are using a linear taper pot, get a log (audio) taper. And vice versa.
Reply 11 years ago
What are those?
Reply 11 years ago
. Maybe this will explain a little better. Assume a 100 ohm pot with a dial calibrated 0-100. . With a linear pot, 25% on the dial will give 25 ohms, 50/50, 75/75, etc. . . Don't have a real good explanation for logrithmic. If the pot gives 10 ohms at 10% on the dial, it will give 100 ohms at 20% and 1000 ohms at 30%. That may not be exactly right, but it gives you the idea. . Ever notice how on a audio frequency response chart the low frequencies are spread out and the high frequencies are jammed together? Same thing.
Reply 11 years ago
ahhh, got it now. The linear pots have a direct relationship, they follow a "linear curve", whereas the taper pots follow a logarithmic curve.
Reply 11 years ago
. Doh! I misjudged your level of knowledge/experience. That's it exactly.
Reply 11 years ago
That's alright! Thanks for all the help!
11 years ago
I have a circuit that will allow adjusting the brightness of LEDs by adjusting the current rather than the voltage. While it's quite a bit more complex, it allows driving many more LEDs and a more linear brightness change. If you'd like, I'll share the circuit with you in private.
Reply 11 years ago
I'm interested, that would be great!
Reply 11 years ago
. It might be more efficient to use the feedback loop to adjust the regulator voltage, instead of dropping it across your 2K pots. Not sure.
Reply 11 years ago
What's the feedback loop? (I'm sorry, all I know about the Vreg is what I picked up from a brief skimming of the spec sheet)
Reply 11 years ago
. PS: if it ain't broke, don't fix it. :)
Reply 11 years ago
It actually is kind of broken, the relationship between the pot's resistance and the intensity of the LEDs is certainly not direct. Hmmmmmmmmm ' I'll try that, definitely!
Reply 11 years ago
. The loop from the regulator output that "feeds back" to the adj terminal (the 1K and 1.4K resistors). This is what sets the output of the reg.
11 years ago
Eureka! I've got it, but I don't know if it's efficient Man, I'm tired. I wasted my whole day on this! (and ACTs)
11 years ago
I don't think that I understand your set up. I seems like you are throwing 3.27V at an LED through a resistor (0-2K Ohm), but putting 2K in front isn't shutting the LED off? - circuit diagram? L
Reply 11 years ago
You've got it right, but I'll draw up a schematic anyway.