#1
Hey, I'm designing an interesting little pedal here and need to know something that would make matters much easier.

In astable operation of IC 555, when the output is "low," and say, we connect an LED's cathode to pin 3 (output), would this work as a ground for the LED (not considering the fact that the output would go high after a certain time)?
Gear:
Schecter Hellraiser Deluxe
Boss DS-1
Crate GTD65

GAS List:
Mesa Boogie Dual Rectifier Roadster
#2
if this topic was any gayer i'd think i'd have to waste my uber charge just to tell an old man to shut up
#3
I'm not sure I completely understand what you're trying to convey, but (I think) this is what you're asking:
-Can I use pin 3 of the IC to ground the LED?
If that's the question, the answer is no. Even if the IC has no output, you can't do that. The output from the IC is of course always has a positive voltage as referenced to ground, even in low output situations. Is there a reason you can't just ground the LED to the PCB?
If you have a schematic I can help you out if you need it. What's this for, anyway?
#4
^^
nope, you actually can

the 555 is a bit of a brute, giving you up to 200mA in either direction
but many(most?) ICs can actually take more current coming in that coming out

but this becomes very useful with microcontrollers when you don't want to use a transistor to drive something (the outputs can usually source about 5mA but can sink 20mA...quite a difference)


heres how to make a pair of alternately flashing LEDs: http://www.kpsec.freeuk.com/images/555leds.gif
Last edited by seljer at Aug 7, 2008,
#5
Quote by seljer
^^
nope, you actually can

the 555 is a bit of a brute, giving you up to 200mA in either direction
but many(most?) ICs can actually take more current coming in that coming out

but this becomes very useful with microcontrollers when you don't want to use a transistor to drive something (the outputs can usually source about 5mA but can sink 20mA...quite a difference)


heres how to make a pair of alternately flashing LEDs: http://www.kpsec.freeuk.com/images/555leds.gif


Thanks, didn't think of that yet. The real reason I want to ground it to the IC pin 3, is for a different purpose than the LED, but I want to keep it a secret till it's done. Wow, that was so gay. Anyway I'll test it, if it doesn't work I'll probably just use a switching transistor to redirect anything coming into the output "loop" to ground if the output is high/low, whichever suits me best.
Gear:
Schecter Hellraiser Deluxe
Boss DS-1
Crate GTD65

GAS List:
Mesa Boogie Dual Rectifier Roadster