Hello, everyone! First time I'm posting a thread.
One of my back-burner projects for a while has been designing a simple resonant 2-pole voltage-controlled filter with an onboard low frequency oscillator.
I got pretty good (and kinda unique...sometimes reinventing the wheel pays off) results up to the point of it being a simple resonant 2-pole POTENTIOMETER-controlled filter, but I seem to stall out when it comes to designing LFO's or voltage-controlled resistances, so I'm looking for advice, recommendations of favorite circuits known to work, and general theoretical pointers...I like understanding what I'm doing!
First the LFO...design goals are:
1) Perfect waveshapes are not that important...squares with no rise-time, for example, actually don't sound too great (they tend to POP really hard at the edges.)
2) I'd like a pretty wide range of frequencies without the oscillator stalling, ranging from "whoa, I forgot that thing was on!" (about .1Hz) to low audio-range (say, 55hz.)
3) Pretty consistent amplitude, both between waveforms and across the frequency spectrum...I seemed to have a REALLY hard time with this when I was attempting it, before.
4) Ideally, it should be able to run on a single supply, possibly as low as 9V. Ideally, it should also not need any weird components, or draw huge amounts of current. Ideally, it should also make me breakfast and iron my clothes.
Feel free to disabuse me of my delusions if any of the above is cripplingly impractical, particularly with respect to...
Voltage-Controlled Resistance!
Basically, I have yet to read an article on this topic that makes much sense to me. (I've read a few manufacturer's papers and felt like I learned a lot about the physics involved but not necessarily much that would help me make design decisions.) I'm looking for practical, hands-on advice about how to implement a resistance that will swing in something APPROACHING a linear fashion with the output of the above function generator. The specific range isn't necessarily SO important, since the caps can be scaled to match it.
1) Again, no weird or exotic components, if it can be helped. I'm open-minded about FET, LDR, OTA, or whatever...but I don't want a solution that's likely to be obsolete or hard-to-find in the near future, or one that's likely to bug out under slightly imperfect conditions. (ex: I'm skittish about the future availability of OTA IC's...they seem to be discontinued left and right.)
2) This may be asking too much, but I'd like to get a useable range of predictable results without relying on a bunch of trimpots or pre-screening of components. I could live with a compromise on the former; the latter is for the birds!
Thanks a bunch in advance to anyone who weighs in on any part of the above!
One of my back-burner projects for a while has been designing a simple resonant 2-pole voltage-controlled filter with an onboard low frequency oscillator.
I got pretty good (and kinda unique...sometimes reinventing the wheel pays off) results up to the point of it being a simple resonant 2-pole POTENTIOMETER-controlled filter, but I seem to stall out when it comes to designing LFO's or voltage-controlled resistances, so I'm looking for advice, recommendations of favorite circuits known to work, and general theoretical pointers...I like understanding what I'm doing!
First the LFO...design goals are:
1) Perfect waveshapes are not that important...squares with no rise-time, for example, actually don't sound too great (they tend to POP really hard at the edges.)
2) I'd like a pretty wide range of frequencies without the oscillator stalling, ranging from "whoa, I forgot that thing was on!" (about .1Hz) to low audio-range (say, 55hz.)
3) Pretty consistent amplitude, both between waveforms and across the frequency spectrum...I seemed to have a REALLY hard time with this when I was attempting it, before.
4) Ideally, it should be able to run on a single supply, possibly as low as 9V. Ideally, it should also not need any weird components, or draw huge amounts of current. Ideally, it should also make me breakfast and iron my clothes.
Feel free to disabuse me of my delusions if any of the above is cripplingly impractical, particularly with respect to...
Voltage-Controlled Resistance!
Basically, I have yet to read an article on this topic that makes much sense to me. (I've read a few manufacturer's papers and felt like I learned a lot about the physics involved but not necessarily much that would help me make design decisions.) I'm looking for practical, hands-on advice about how to implement a resistance that will swing in something APPROACHING a linear fashion with the output of the above function generator. The specific range isn't necessarily SO important, since the caps can be scaled to match it.
1) Again, no weird or exotic components, if it can be helped. I'm open-minded about FET, LDR, OTA, or whatever...but I don't want a solution that's likely to be obsolete or hard-to-find in the near future, or one that's likely to bug out under slightly imperfect conditions. (ex: I'm skittish about the future availability of OTA IC's...they seem to be discontinued left and right.)
2) This may be asking too much, but I'd like to get a useable range of predictable results without relying on a bunch of trimpots or pre-screening of components. I could live with a compromise on the former; the latter is for the birds!
Thanks a bunch in advance to anyone who weighs in on any part of the above!