Blinking Rate Led Infos

[mickeybellinello]

Hi to all!

here I am again with another question.

I built a phase 90 clone and checking tonepad site I see that it is possible to add a rate led to this circuit.

mainly it must connect a led pin to GND and the other to the lug 7 of IC1.

All works well but the Led works in ON/OFF mode.

Is it possible to add a smooth transition to the blink (hope to explain in the right way)?

Thanks

[PRR]

> smooth transition

No simple way.

This type oscillator has a strong output on the square (on/off) wave, but only weak signal on the ramp wave. Enough to swing some JFETs, not enough to fade an LED.

[mickeybellinello]

> smooth transition

No simple way.

This type oscillator has a strong output on the square (on/off) wave, but only weak signal on the ramp wave. Enough to swing some JFETs, not enough to fade an LED.

Thanks for your reply..so no way?

[Rob Strand]

Thanks for your reply..so no way?

It's not impossible.  If you had to to do it you could do it.
It's a matter of how much extra circuit you want to add.

[mickeybellinello]

It's not impossible.  If you had to to do it you could do it.
It's a matter of how much extra circuit you want to add.

Thanks for your reply!
Unfortunely not a lot of room in the enclosure for adding big circuits but...what kind of stuff do I need?

[antonis]

Probably a LED driver transistor (or op-amp) but you should mess up with current gain & resistors tweaking..

[toneman]

Thanks for your reply..so no way?

It's not impossible.  If you had to to do it you could do it.
It's a matter of how much extra circuit you want to add.

just need a single buffer opamp off of the triangle capacitor to drive 1 or 2 leds. 
Preferably a fet input opamp. i.e. TL061, 71 or 81.
Muvh Easier than 1 or 2 or 3 transistors.

[Rob Strand]

just need a single buffer opamp off of the triangle capacitor to drive 1 or 2 leds.
Preferably a fet input opamp. i.e. TL061, 71 or 81.
Muvh Easier than 1 or 2 or 3 transistors.

That's should work. 
It's actually a little more wiring than a transistor because you have the extra power pins.

I was thinking of using a MOSFET.    In this case the MOSFET Vgs on provides one voltage drop and the LED supplies the another.   

With these changes:
- 9V
- MOSFET 2n7000
- R = 470 ohm  ; tweak to taste
- gate of MOSFET to 15uF LFO cap.

A high-gain BJT might work in the same circuit if you add the extra LED in the emitter (which is not visible).  Any loading from the BJT is compensated for to some extent by the fact the Schmit trigger maintains the *output* swing on the cap.  If the BJT heavily loads the cap it could throw-out the timing and perhaps the duty cycle.

To the OP: The extra voltage drops helps emphasize the changes in the LED current (the on/off'ness ).  In all the above solutions the voltage drops are kind of rough but probably good enough.  To do better you would need a different configuration for the added opamp or some sort of differential-pair.  You would then set-up another reference using a divider off Vref which would be just a bit below the minimum voltage swing of the LFO.   Much more complicated than the above.

If the above aren't good enough you can tweak the voltage drop by adding a small signal diode in series with the LED, then tweaking the resistor.  Watch out making the resistor too small, say less than 220 ohm.

For the MOSFET, you can use a smaller source resistor to set the off-side brightness then add another resistor between the drain and the supply to limit the LED on-current without risking frying the LED; the might look a bit more on/off.[Actually the drain resistor might be a pain to tweak an the results could vary depending on the supply].

Anyway,  often these simple circuits need some tweaking to help them along.

[mickeybellinello]

just need a single buffer opamp off of the triangle capacitor to drive 1 or 2 leds.
Preferably a fet input opamp. i.e. TL061, 71 or 81.
Muvh Easier than 1 or 2 or 3 transistors.

That's should work. 
It's actually a little more wiring than a transistor because you have the extra power pins.

I was thinking of using a MOSFET.    In this case the MOSFET Vgs on provides one voltage drop and the LED supplies the another.   

With these changes:
- 9V
- MOSFET 2n7000
- R = 470 ohm  ; tweak to taste
- gate of MOSFET to 15uF LFO cap.

A high-gain BJT might work in the same circuit if you add the extra LED in the emitter (which is not visible).  Any loading from the BJT is compensated for to some extent by the fact the Schmit trigger maintains the *output* swing on the cap.  If the BJT heavily loads the cap it could throw-out the timing and perhaps the duty cycle.

To the OP: The extra voltage drops helps emphasize the changes in the LED current (the on/off'ness ).  In all the above solutions the voltage drops are kind of rough but probably good enough.  To do better you would need a different configuration for the added opamp or some sort of differential-pair.  You would then set-up another reference using a divider off Vref which would be just a bit below the minimum voltage swing of the LFO.   Much more complicated than the above.

If the above aren't good enough you can tweak the voltage drop by adding a small signal diode in series with the LED, then tweaking the resistor.  Watch out making the resistor too small, say less than 220 ohm.

For the MOSFET, you can use a smaller source resistor to set the off-side brightness then add another resistor between the drain and the supply to limit the LED on-current without risking frying the LED; the might look a bit more on/off.[Actually the drain resistor might be a pain to tweak an the results could vary depending on the supply].

Anyway,  often these simple circuits need some tweaking to help them along.

Thanks so much! Unfortunely I red the post only this moment (it's the second time..probably i have problems with mail notification).
I red what i wrote and the circuit is similar to what i found in madbean nomnom reference.
I started a new topic about that circuit. If you would like please take a look.
In the meantime thanks so so for your advice and explanation.
I'm getting a lot of useful knowledge thanks to you.

[drummer4gc]

Different pedal but this worked for me: https://www.diystompboxes.com/smfforum/index.php?topic=107444.0

[mickeybellinello]

Different pedal but this worked for me: https://www.diystompboxes.com/smfforum/index.php?topic=107444.0

thanks, I'll take a look immediately