Fading / Pulsing a led strip about 20 individual leds using analog / non UC

[ErnieH]

Hi can some one please help me light up about 20 leds on a led strip lighting please. I know how do use a 555 timer to illuminate 1x 5mm bright led, but I want 2 use about a foot long strip led 12v, like u use in kitchens.

Some have suggested PWM but i don't know how to setup. I was hoping for an analog circuit diagram ready 2 go, tried & tested that works please.

Thank you
ErnieH

 

[audioguru]

Most 12V LED strips use three LEDs in series and with a series resistor. Then you will have 21 LEDs.
Each group of three LEDs use 20mA so seven of them use 140mA which a 555 can provide.

The output of a 555 is a squarewave which can simply blink all LEDs on and off at the same time. Then they will be pulsing. The datasheet of a 555 shows the simple oscillator circuit that will do it.

For fading then the weak signal at the capacitor of the 555 circuit can be used. Then a Darlington transistor follower must take the weak fading signal and strengthen it so it can drive all the LEDs. I have schematics of fading LEDs that use a dual opamp and a transistor.