555 PWM dim-to-bright LED circuit

Hi All,

I know that something similar must have been posted here before, but I was looking back and couldn't find exactly what I needed.

I need to build a circuit that make 3 LEDs go from dim to bright and back again in a loop. Pretty simple stuff, but I'm new. I want to use a 555, as I'll be using it for something else in the circuit too. I understand you have to PWM, but not exactly sure how that would work.

Anyone have a link to similar circuit diagram? Or an exact circuit diagram? :lol: Sorry if this has been posted before.

Thanks so much.

Do you want all 3 LEDs to fade together, or do they need to fade one after the other?

they all need to fade together. sorry, should have been more clear.

The voltage across the timing capacitor of a 555 oscillator ramps up and down similar to a triangle wave. A darlington transistor can be used to follow the voltage and the LEDs connected in series and in series with their current-limiting resistor can be driven by the darlington's emitter. The circuit's supply voltage, the total voltage of the LEDs and the voltage drop of the darlington must be calculated to dim and brighten the LEDs. The voltage at pin 5 of the 555 can be varied with a pot for "fine tuning".

audioguru said:

The voltage across the timing capacitor of a 555 oscillator ramps up and down similar to a triangle wave. A darlington transistor can be used to follow the voltage and the LEDs connected in series and in series with their current-limiting resistor can be driven by the darlington's emitter. The circuit's supply voltage, the total voltage of the LEDs and the voltage drop of the darlington must be calculated to dim and brighten the LEDs. The voltage at pin 5 of the 555 can be varied with a pot for "fine tuning".

Click to expand...

thanks, i'll try making sense of this. appreciated.

Look at:
**broken link removed**

Replace the first 555 in Fig.86b with the ramp generator in
Fig.86a.

<als>

fredsm said:

Look at:
**broken link removed**

Replace the first 555 in Fig.86b with the ramp generator in
Fig.86a.

<als>

Click to expand...

schematics! so much easier to understand than words. :lol: thanks so much. i'll try it out tomorrow...

fredsm said:

Look at:
**broken link removed**

Replace the first 555 in Fig.86b with the ramp generator in
Fig.86a.

<als>

Click to expand...

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