Pulsing LED - MXR phase 90

[Bent Penguin]

Hi, I just modded my Phase 90's LED to blink with the speed setting. I was hoping it would fade in and out but I'm just getting a binary off and on blink. Is this the best I can do? Did I set my sites too high? Am I a hopeless dreamer?

I'm using a cheap green diffuse LED if that matters.

Thanks.

[niftydog]

put a large-ish cap in parallel with the LED. Might take some experimenting to find a good value, and it might look better at slow speeds than high speeds... but it's a quick fix.

[vdm]

hey, if you're just tacking that off from the oscillator like the phase 45 mod, then it's following the square-wave that's generated from the oscillator. The cap idea is a good one, and ill second that - just trying to give you some knowledge as to why... if only i really knew myself :?

trent

[niftydog]

you may need, in that case, some isolation between the oscillator and the LED. A large-ish (here I go, all vague again!) resistor inbetween them might suffice.

[Bent Penguin]

put a large-ish cap in parallel with the LED. Might take some experimenting to find a good value, and it might look better at slow speeds than high speeds... but it's a quick fix.

Not series? I tried a .047 and a 10uf in parallel but didn't notice any change.

[Bent Penguin]

hey, if you're just tacking that off from the oscillator like the phase 45 mod, then it's following the square-wave that's generated from the oscillator. The cap idea is a good one, and ill second that - just trying to give you some knowledge as to why... if only i really knew myself :?

trent

Yeah, I got the idea from the MXR45 mod. The multimeter shows the voltage going smoothly up and down but that just may be the delay in the meter.

[bazzwazzle]

try like a 100 uf cap

[Bent Penguin]

you may need, in that case, some isolation between the oscillator and the LED. A large-ish (here I go, all vague again!) resistor inbetween them might suffice.

I have a 2.2k there now which was the original resistor for the LED when I got it. Should I go bigger?

Thanks for all the help guys.

[bazzwazzle]

note above ^^

EDIT: you might want to go bigger resistor but i'm not sure on that. try it out.

[Bent Penguin]

try like a 100 uf cap

Nope, still nothing, and I tried it both ways.

[bazzwazzle]

i remember seeing a method involving a transistor to do it. let me see if i can find it.

[bazzwazzle]

EDIT: dude forget what i just said, cause you already have the pulsing. A larger cap should really do the trick.. i dunno

[bazzwazzle]

do you use a transistor to do the blinking? can i see the schematic or something?

[niftydog]

leave the LED resistor alone - treat the LED and it's current limiting resistor as if they are one component.

Add a large resistor in the signal path from the oscillator to the LED. Now, put a large cap in parallel with the LED.

Code Select Expand


         added resistor
           >1000 ohms
             ___
Oscillator o-|___|-o---o--------o
                      |        |
                      V LED    |
                      -        o
                      |        |  added capacitor
                      |       ---   >100uF
                     .-.      ---
                     | |       |
                     | |       o
                     '-'       |
                      |        |
                      o--------o
                      |
                     ===
                     GND


[mikeb]

You might also need to use an active component (transistor / opamp) to adjust the voltage for the LEDs characteristics, i.e. when the waveform bottoms out make the LED just on, when the waveform 'tops' out then make the LED be on at full brightness. For perfection, this could mean scaling the range and transforming the amplitude of the LFO voltage ... and as side effect you won't add any current load to the LFO (although whether or not this is a problem with that circuit I don't know).

Mike

[Bent Penguin]

leave the LED resistor alone - treat the LED and it's current limiting resistor as if they are one component.

You may pick any item from the top shelf

That did it, thank you all. Connecting the cap to the other side of the resistor than the LED is on did it.

Now the wierd stuff. 10uf is too small, 100uf gives a nice smooth pulse Yippee! But it also slows the frequency down, more so it seems as I turn the knob to faster. It also seems to change the effect to a more wah wah type sound so I'm going to add the cap on a switch and experiment without trying to hold the cap with my fingers and play. More to come...