buzz's description will definitely work. There are a couple of caveats.
On November 28, 2016 at 11:17, GotGame said...
Doing it that way will also create a flicker upon startup and fadeout on most strips.
So if the customer is okay with that, then is a good, cheap method.
If the LEDs all turn on at the same voltage, then the only thing you might call flicker would be the LEDs not turning on simultaneously. Wati. I thought about that a bit.
The voltage across the capacitor is increasing gradually. When the LEDs first turn on, they draw current from the cap and that should lower the voltage, perhaps enough for the LEDs to go into a relaxation oscillation mode (look that up). So, yeah, they could flicker.
But I don't see them flickering on the fade to zero. Again, they might not all go off at the same time.
Worse is the effect the resistor will have on your setup. It will always be in series with the LEDs, so there will be a constant voltage drop across it. If your resistor has to be a hundred ohms and the LEDs draw a half amp, once the cap is charged, the resistors will have a voltage drop of 100 x 0.5 = 50 volts! So a 62 volt supply would be needed for 12V LEDs.
Look at your actual product and measure your actual current draw. I think you'll find the resistor and capacitor idea unwieldy. If you amplify your control capability with one transistor, all of this will be much simpler.
