[sdiy] Adding signal LED's to an LFO module

[Scott Bernardi]

I've done this on an LFO. It works great - you can even tell the
difference between a sine and a triangle output at lower frequencies.
You do need to buffer it with an additional opamp from your output.
You can do the same thing with a "three leg" bipolar LED by driving it
from a discrete differential pair. A few more parts, but the advantage
is that there is a constant draw on the power supply rather than current
spikes.
See http://members.home.net/sbernardi/elec/og2/og2_lfo.gif 
You might want to add a couple of 150 ohm resistors in series with the
Q5 and Q6 emitters on that circuit.

patchell wrote:
> 
>     Here is a "keen" idea.  Use one of the bi-color LEDs (the one that has two
> legs, not the three leg job).  Connect it through an apropriate sized resistor
> to one of the outputs.  I am not familiar with TomG's SBM board, but I am
> willing to bet one of the waveforms is a triangle.  I would connect it to that
> output.  You probably only want about 5 mA flowing through the led.  Anyway, at
> low frequencies, you will see it alternate between red and green.  At high
> frequencies, it will be yellow (or something like that).  Anyway, just a
> thought.
> 
> vitreousflux wrote:
> 
> > I have an EFM SBM board that has 2 LFO's - I would like to add two LED's to
> > each LFO, that will fade in and out of brightness, in sync with the LFO
> > phase. (one LED for positive phase, one for negative phase)
> >
> > I'm thinking that adding a simple opamp or two to do this would do the
> > trick, but I'm a bit of a newby when it comes to original circuit design.
> >
> > Can anyone assist?
> >
> > Rob
> 
> --
>  -Jim
> ------------------------------------------------
> * Visit:http://www.silcom.com/~patchell/
> *-----------------------------------------------
> *I'm sure glad Merry Christmas comes just once a year
> * -Yogi Yorgensen
> ------------------------------------------------

-- 
Scott Bernardi
sbernardi at home.net