Hi AAC,

I'm busy with a circuit, where many solutions have been suggested. this thread is a spinn-off of this thread: http://forum.allaboutcircuits.com/threads/again-led-dimming-and-fading-on.108787/page-10

We have a working ramp up, but I realized that we probably need a ramp down aswell, (I'm a noob, at the moment you could say I play lego, get bits and bits and fit it all together)

So if anybody skilled enough could provide me with a ramp down voltage circuit (or teach), I'll put it together with the theremin I'm using... add the ramp down... hopefully get my fart sound which at the moment seems like an impossible task

please, of course, if it's not too much trouble

MORE INFO
24s-29s is all that is relevant

the pic is the circuit layout of the theremin, you will notice that the 2 phototransistors, which I'm not going to use, I wanna make set notes for making it a fart piano, but you will notice that it's a configuration of 2 transistors in parallel, the one leading and the other following, so light on the one makes it go high and light on the other one make it go low (dunno which is 1 and which is 2), also the man in the video adds distortion -- dunno what distortion, to make the fart even more real, but I'll settle for just the normal, very realistic fart in the 24s-29s part of the video. First we thought we needed 2 ramp ups at different slopes, but didn't understand the leading - following configuration [http://www.globalspec.com/learnmore/optics_optical_components/optoelectronics/phototransistors --- this is where I learned that the one transistor in parallel goes high while the other goes low as light activates it]


PS I'm also currently investigating microcontroller solution, but I think this theremin is the best solution, if I can get it to work!

 

the ramp-up circuit

 

Here's a dual-ramp circuit. If the Control voltage is high/low the output ramps down/up.

 

Here's a dual-ramp circuit. If the Control voltage is high/low the output ramps down/up.
View attachment 84184

couldn't find symbol lm324

 

LM324 is a popular single supply quad opamp from National Semiconductor, now Texas Instruments.

http://www.ti.com/lit/ds/symlink/lm124-n.pdf

 

LM324 is a popular single supply quad opamp from National Semiconductor, now Texas Instruments.

http://www.ti.com/lit/ds/symlink/lm124-n.pdf

yeah, thx, but its LTspice that complains about not knowing the LM324

 

yeah, thx, but its LTspice that complains about not knowing the LM324

will a 741 or 393 work, I have them on hand, the LM324 I have to order (which I have no problem doing whatsoever)

EDIT: found 2 LM324 in a miscellaneous LM drawer

 

Here's a dual-ramp circuit. If the Control voltage is high/low the output ramps down/up.
View attachment 84184

Hi @Alec_t , could you please provide me with the files that allows LTspice to see the LM324, at the moment during load time it says: "Couldn't find symbol(s): LM324"

I actually need to set the ramp angle, and I can't load your .asc in LTspice, it doesn't have the lm324 in its library