LFO-driven LED for Opto-controllers.

[lovekraft0]

Here's something that may be of interest - it's a simple LFO with triangle and square wave outputs driving an LED for use with Vactrols or the Siliconix optos. Frequency range and depth/drive current are easily tweakable, the parts count isn't too bad, and there's nothing fancy involved either. It works on my breadboard (using a new, non-mojo 4558) - if I come up with a good vero layout, I'll post it, if anybody's interested.

If you notice any potential problems or obvious mistakes, please let me know. I hacked this together for a simple, improvised tremolo for a friend of mine, but maybe somebody can use it for something cooler. 

[petemoore]

  Can or can be made to drive 4 LED's?, it would make a nice mod to an LED/LDR phaser.
 

[lovekraft0]

Didn't think about multiple LEDs - it's probably easiest to use a separate follower for each LED, and use a single pot to control depth. Something like this might work:

Here's where there's room for a lot of experimenting - I think you could easily run 6 (and possibly even 8?) followers/LEDs without loading the oscillator too badly, but that's not verified (it works in simulation, but simulators lie  ). Also, as configured, R19 sets the operating point of the followers, so the modulation will always vary between  zero LED current and whatever peak you set. I'm wondering if adding a cap between R19 and ground would block the DC so the current would vary around the center set by the 4.5v operating point of the oscillator. I'll play with it some more when I get time, and see if there are any problems I haven't foreseen. Feel free to hack, tweak and bend as desired, and let me know if you get positive results.

[Paul Perry (Frostwave)]

Try running the leds in series, before complicating things!