555 output question

[FractalCat]

I have a schematic of the 555 IC where the output pin is connected to an LED and also to a resistor and capacitor and then to ground, which to me looks like an RC circuit or a low pass filter. The LED is not in series with the resistor and capacitor they have different connections. What's going on here? What is the purpose of the resistor and capacitor in this circuit?

Thanks

Fractal Cat

 

[bertus]

Hello,

Could you post a schematic?
You can upload picture files upto 300 kB.

Bertus

 

[FractalCat]

Hello,

Here's the schematic. What are the resistor and capacitor for in this circuit?

Thanks

FC

 

[Audioguru]

The maximum allowed output current of an ordinary old 555 is 200mA that will quickly burn out an ordinary LED that has a maximum allowed continuous current of 30mA. Therefore the LED needs a series current-limiting resistor.
The 555 might be a modern Cmos LMC555, TLC555 or ICM7555 that has much less output current.

EDIT: Your ordinary old NE555 has a resistor R1 to limit current to the LED.
I do not know why there is R2 and C1 at the output of the 555 to ground.

 

[FractalCat]

I'm aware of this but it doesn't explain the purpose of the capacitor in series with the other resistor.

 

[Harald Kapp]

R2+C1 make no sense. Where did you get that schematic from? An explanation may be found on that website.

 

[crutschow]

I also can think of no useful purpose for R2-C2.

 

[FractalCat]

This schematic was taken from Electronics for Dummies as a hobbyist project. So what are the series resistor and capacitor doing
in this circuit?

 

[bertus]

Hello,

Strange, the book I got shows a different circuit:

There is no resistor / capacitor combination on the output.

Bertus

 

[FractalCat]

Ahh, now I understand. This makes more sense. So the book has a mistake. Well, I've seen that before with
other texts.

Thanks Bertus

 

[bertus]

Hello,

The schematic that you posted is from this version of the book:
https://archive.org/details/electronicsfordummies_201910

When you look at the partlist on page 310, C3 is not mentioned:

Bertus

 

[AnalogKid]

In the first image, C3 is supposed to be the LED. The clue is the resistance value of R3, which is correct for a normal small LED and VCC values up to +12 V.

ak