Replacing an expression pedal with an automated device

[danoisefactory]

Ok, cool!

I'll fool around with that to see if i can make the feedbackloop less harsh and brutal.

I'm still pretty happy with myself, and currently thinking about all the things i might do with this new knowledge haha!

[ginsengbob]

I did this when I made the bent MM-4.  You are going to want to first build an oscillator, then feed the oscillator into an H11F3 or photocell to get the variable resistance.  Sine vs. Triangle modulation is basically the same 90% of the time, it is definitely not worth the extra work to get a sine wave.  My oscillator of choice is this one:

http://experimentalistsanonymous.com/di ... %20LFO.gif

You can get a different range out of the LFO by using a larger pot and changing that cap value.  You should feed the output of this into a simple, noninverting buffer:

http://www.seas.upenn.edu/~ese205/Labs0 ... age019.gif

You now have three op amps, might as well put it all in a quad op amp package.  Then, you might want to wire a simple volume pot (one side lug to the noninverting buffer output, one side lug to Vb, and the center lug is the out) into another noninverting buffer - this is the LFO amount pot.  Wire the output of this second noninvering buffer, whose output should go into a 470 ohm or so resistor, into the + input of the H11F3.  - input to ground, then you have 2 pins for the varying resistance.  If the expression pedal uses 3 connections, one for center, and two sides, then you will need to wire an inverting buffer, and a second H11F3.

Colin
What does this do when you take the output of the LFO and run it through a non inverting buffer before sending it to the h11f3?

Is it crucial?

[ginsengbob]

Also
Is there a way to have the lfo control a led AND the h11f3 ?
When I try to hook them both up they don't work.
Only 1 or the other.

Thanks

[expanoncolin]

Also
Is there a way to have the lfo control a led AND the h11f3 ?
When I try to hook them both up they don't work.
Only 1 or the other.

Thanks

Make sure they both have their own current limiting resistor.  That is, it should go LFO out -> resistor -> LED, and separately LFO out -> another resistor -> H11F3.

The noninverting buffer ensures that the LFO output sources the same current regardless of the wave shape pot's position.  It allows the LFO to function as an ideal current source.  It's not totally necessary depending on the application.

-Colin

[ginsengbob]

Ok, I got the  led and h11f3 working at the same time.
When I turn the lfo amount down past a certain point the led stops lighting but the h11f3 is still sending resistance.
Is there an easy way to increase the voltage to the led and keep it working while the h11f3 is getting lower voltages?
I tried increasing the resistor on the h11f3 but I couldn't find a sweet spot that kept the h11f3 working at it's full range.

As far as the opamp buffer I didn't notice enough difference to justify having a bigger chip.
I'm always running out of room in my projects and want to try to keep everything small and simple when I can.

Thanks Colin

[expanoncolin]

Ok, I got the  led and h11f3 working at the same time.
When I turn the lfo amount down past a certain point the led stops lighting but the h11f3 is still sending resistance.
Is there an easy way to increase the voltage to the led and keep it working while the h11f3 is getting lower voltages?
I tried increasing the resistor on the h11f3 but I couldn't find a sweet spot that kept the h11f3 working at it's full range.

As far as the opamp buffer I didn't notice enough difference to justify having a bigger chip.
I'm always running out of room in my projects and want to try to keep everything small and simple when I can.

Thanks Colin

Try lowering the LED resistor, or try using a noninverting buffer to the LED! (between LFO output and LED resistor)

-Colin