soft on/off switch

[robobot]

I need a schematic for a soft on/off switch so I can have lights fade in when I turn the switch on and fade out when I turn the switch off. If it's possible, I want one that doesn't use IC's or inductors, and it should be as simple as possible.

[Chapel]

Like a rocker switch or a button switch?

[robobot]

rocker switch

[robobot]

OK, I figured something out, but I can't get it to work right because I'm not sure what values the components should have.

------------------------- V+
|	   |
SW	   |
|	   |
R1	   |
|	   c
|---------bQ
|	   e
|	   |
C	 Load
|	   |
|	   R2
|	   |
--------------------------- GND

Q is a transistor. e, c, and b are the different leads.

What exactly does each component do, and how do you determine the appropriate values? I'm going to need to make 2 of these: one for my case lights and one for my HDD activity light.

[robobot]

Made some progress. It fades out nicely, but it still doesn't fade in right. If R1 is too high, the LED won't light up all the way, and if it's too low, the LED fades in way too fast (almost instant).

[Aero]

good luck. I hve been trying to learn some circuitry because I only know enough to light some LED's, and I want to build a wireless link for my TI-83+ calculator, I have the schematics, jst need to learn what everything is :p. Good luck on yours once again, post some pics or movies if you can, this would be prety cool to see.

[robobot]

Good news! I figured it out. I increased the value of C a lot and added another resistor R3 in parallel with the load and ballast. The larger value of C makes the fade-in longer because it takes longer to charge. Since it takes longer to charge, it also takes longer to discharge, so R3 was put in to draw more current from C during the fade-out, making a shorter fade. It's a pretty sweet effect. I can't wait to put it on my HDD activity light. I'll post a full schematic with correct component values when I finish.

[Malatory]

I ment to post this yesterday and say take the IC chip out of the loop and use the on/off switch you want in place of it. But since I am at work .. some things tend to be forgotten until later.

http://www.metku.net/index.html?sect...eyez/index_eng

and it would have explaned the CAP issue you went though.

[robobot]

That's pretty much what I have already. For SW, I use a transistor switch wired to the HDD light output. The photodiode/phototransistor thing works too, but the regular transistor is much simpler, and I already have one. Either way, you need one of the two options. wiring in the input directly doesn't work.

however, for a regular light, a regular toggle switch is fine.

Schematic to be posted soon.

[robobot]

OK. Here's the final working schematic for the HDD light. Please excuse my mad MSpaint skillz.

R1: 4.7k ohms
R2: 68 ohms
R3: 68 ohms
C1: 100 uF
Q1 and Q2: any PNP transistors

IN connects to the LED output on the disk controller/motherboard
OUT connects to the HD activity LED
+5V and GND connect to the power supply