# Electronics Noob LED circuit help

Discussion in 'Modding' started by tommarndt, 13 Nov 2003.

1. ### tommarndtWhat's a Dremel?

Joined:
10 Nov 2003
Posts:
6
0
ok, im a noob at electronics, so i need some help with this.
I have a crapload of LEDs that i want hooked up. All from the same molex connector. And each led will be turned on by a switch, and will fade out.

I was going to hook them all up in parallel with a switch before each resistor and LED. Im not sure how to draw some of the symbols, so if you can't tell the V is the LED, /\/\/ is the resistor, and the S stands for switch. Would this design work?
Code:
```               _
----V--/\/\/---S---
|   _             |
----V--/\/\/---S---
|   _             |
----V--/\/\/---S---
|   _             |
----V--/\/\/---S---
|   _             |
----V--/\/\/---S---
|                 |
Ground|                 |+5v
```
And if it can work, where would I throw the capacitor s in to give them the fading out effect?

BTW, how many LEDs would you be able to have on at the same time running off of one Molex connector?

Thanks a lot guys.

2. ### whypick1The über-Pick

Joined:
17 Oct 2002
Posts:
2,014
2
For future reference, I use |>| for diodes, _/ _ for switches and v^v^v for resistors.

Anyway, onto your question. I can't think of any simple way to get a simple fade out effect. A typical RC circuit will have a fade in and fade out effect. If you want to pursue that method, then 1 LED circuit should look like this

Code:
```                 R       C
+5v - - _/ _- -v^v^v- - -||- - - - - - - GND
|- -v^v^v- - -|>|- - |
R-LED
```
LED should begin to illuminate after about 1 time constant (R*C), while it will be at full-brightness after 5 time constants.

3. ### cpemmaEcky thump

Joined:
27 Nov 2001
Posts:
12,328
55
I've a bench psu with a led "on" indicator that has a fairly slow fade out from the smoothing cap, so that would have
Code:
```      /S          R       LED
12v--o  o--+---\/\/\/----->|----+
|+                   |
=== cap               |
-+-                   |
|                    |
0v---------+--------------------+
```
The fade may work better from a 12v supply than from 5v, try it with a 470uF 16v cap and 2k resistor and see how it goes.

2k is not a typo.