This is probably a very easy question, but I've been trying for several weeks now to create a simple circuit that "fades in" some LEDs using only discrete components like resistors, capacitors, inductors, (photo) diodes, transistors, and a voltage source.
Using only discrete parts (no ICs), how do I "fade in" a few LEDs over the course of a second or two?
I've managed to create the opposite, the "fade away":
- +Volts connected to "RC" and then to "PL" and then to ground in series
- RC is a resistor and capacitor in parallel
- PL is roughly some leds in parallel: PL1 and PL2 in parallel
- PL1 is a LED and resistor in series
- PL2 is three LEDs and resistor, all in series
When powered up (at +6V with the RC using 1K ohm and 2200uF) all LEDs immediately light (no fade in at all), but over 2 seconds the triple LED (PL2) fades to black.
I can of course make this using an Arduino and the PWM output pins to make intricate fade in and fade out patterns, but the circuit is to demonstrate using a simple transistor to switch a system on, and if I'm using a microcontroller to drive that system, I might as well have the transistor trigger my laptop to play a youtube video.