LED Buffer Question

Wild Zebra · Posted: Tue Sep 20, 2005 12:02 pm Post subject: LED Buffer Question

I originally had an LED for my LFO and my power switch. Well I unhooked the LFO one because it seemed to be drawing enough current to effect my osc'ers even when the LFO wasn't patched. Catch my drift?
Well I know its just for show, but its already in my panel so I'm wondering how I could easily (emphasizing EASILY) fix this. Someone said a buffer. Would this require another battery? Any suggestions?
Everyone knows blinking LEDs are cool, and I wanna be cool right? Cool

Macaba · Joined: Jul 13, 2005 Posts: 160 Location: UK

Wild Zebra · Posted: Tue Sep 20, 2005 1:21 pm Post subject:

So I'm a big dummy can you help out alittle more. I guess thats an op amp? What kind? And how would I hook it up to this.

The one on the left. Thats what dangling behind my sound lab

sound_lab_led_indicators.gif

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Macaba · Joined: Jul 13, 2005 Posts: 160 Location: UK

Well the diagram I posted is a voltage follower, it would now seem that it wouldn't fix anything in your case. The job of it is to buffer a voltage at a gain of 1. So the extremely high input resistance means that it doesn't draw any current from the input (negliable) and the low output resistance means you can draw alot from it (limit on common op-amps of 30ma).

But that transistor arrangement should mean that you are not drawing too much from the LFO circuit, so someone will have to step in and offer some insight.

Perhaps you need a new battery?

Wild Zebra · Posted: Tue Sep 20, 2005 1:42 pm Post subject:

Thanks,

Thats what I thought at first, new battery that is. Then I put new ones in
and it still was pulling it down, but I'm a cheapskate so I always buy batteries from the dollar store. Anyway new batts didn't work. So I unhooked it. I recently said f it and started buying duracel, but I haven't hooked it (LED) back up. Maybe I'll get some freshies and try it again. Thanks for the help and maybe someone else will give a hint in the meantime.

Calamardo · Joined: Apr 16, 2006 Posts: 9 Location: Argentina

Hello. Im planing to add the on indicator but is somethig that i cant understand: the schem of led mod shows C16 pin 1 that join to 47k resistor, and in the schem of power supply C16 is the 9+ that is connected to resistor of the led. Is that right??

jksuperstar · Posted: Mon Aug 14, 2006 6:24 pm Post subject:

Well, you could hang the LED on a seperate 9v battery, just shared the grounds and everything else should work (given that transistor layout). You could also try some bypass cap near the LED. Though with the rate of an LFO, it might need to be beefy!

Wild Zebra · Posted: Tue Aug 15, 2006 6:32 am Post subject:

I hooked the power up just like it shows. I never got the lfo led to work. It always just "pulled down" on my osc. even if it wasn't activated.

Calamardo · Joined: Apr 16, 2006 Posts: 9 Location: Argentina

Sorry but i cant understand yet. In the schem: Are both resistors (1k and 47k) connected to +9v?.Whats the purpose of the transistor in there?

Uncle Krunkus · Posted: Thu Aug 24, 2006 1:25 am Post subject:

Hey Calamardo,
I see what you mean. You don't actually need the transistor to make a power on indicator. Just the LED and a 1K resistor across 9V will do it. I'm not sure why Ray did it with the transistor. Maybe someone will chime in with a good reason.

Calamardo · Joined: Apr 16, 2006 Posts: 9 Location: Argentina

ok!, thanks alot. So, now the schem is: +9v --> 1k resistor --> led --> ground??

Uncle Krunkus · Posted: Thu Aug 24, 2006 6:27 am Post subject:

Affirmative! Smile

Wild Zebra · Posted: Thu Aug 24, 2006 7:28 am Post subject:

Thats a good question. Did you you get the LFO indicator working?