RES: [sdiy] Question about LEDs

[Roy J. Tellason]

On Tuesday 07 April 2009 12:02:38 pm Luís Marka wrote:
> On a related note, I have bicolor LEDs for modules that produce both
> positive and negative outputs - my LFOs, for example.
> In order to activate those accordingly (RED when the output is positive,
> GREEN when it goes negative), I had to use a number of components in the
> LED drive circuitry. Positive is fine: resistor + NPN transistor + LED +
> current limiting resistor. Now, for the negative side I had to first invert
> the input via one op. amp at unitary gain, then it goes diode (so only the
> negative semicicle is taken in account) + resistor + transistor + LED +
> resistor. The LED is a common-cathode (3 wire) LED.
>
> Is there a simpler way I could have done it?
>
> Luis Marka

Yes.  A couple of transistors,  set up with appropriate resistor values so 
that the midpoint on your waveform has both LEDs turning on by the same 
amount.  Two transistors,  four to six resistors...

> -----Mensagem original-----
> De: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl]Em nome de Oren Leavitt
> Enviada em: terça-feira, 7 de abril de 2009 05:48
> Para: synth-diy at dropmix.xs4all.nl
> Assunto: Re: [sdiy] Question about LEDs
>
>
> Each blinking LFO LED is a little mouth saying
> "me!...me!...me!...me!..." when one approaches the LFO panel with a
> patch cord.
> - Oren - The only dumb questions are unasked ones
>
> Magnus Danielson wrote:
> > Jason Proctor skrev:
> >>> This may seem like a dumb question, but when you have a module such as
> >>> a simple LFO with a rate-indicating LED -- something like the MOTM-390,
> >>> say --
> >>> is the LED typically always blinking, even when nothing is plugged
> >>> into the
> >>> circuit, or is it typically deactivated somehow when the module is
> >>> not being
> >>> used?
> >>
> >> the LFO is running regardless of whether it's plugged into anything,
> >> therefore yes, the LED blinks.
> >
> > As they should.
> >
> >> i just unplugged my MOTM-320s from their duties, and they are blinking
> >> away merrily.
> >
> > Asking their master "please don't forget me, I want to assist you in
> > your creativity". :)
> >
> > Yes, I think they really *SHOULD* blink...
> >
> > Cheers,
> > Magnus
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