9V dual-wave LFO circuit
Kicking things off here with a super simple circuit I found via electro-music.com forums. It's originally by experimentalistsanonymous.com, but this vero-board layout is by kxspxr (Nov, 2008).
Vero-board layout
Original circuit (same as above)
So far I've only breadboarded the circuit, but it seems to work quite well. I came across some mods on some forums, which I lost pretty swiftly (will post here if I do find them), but the basic gist of the mods from memory was to swap the 100K pot to 1M and the value of the 1µF to something else (very vague, I know - can't remember if it's higher or lower) to get super fast and super slow oscillations.
On the breadboard I've made 2 of these which I'm using to power two LEDs which are each surrounded by multiple LDRs. Basically a vactrol set-up. The LDRs are hooked up around my synth to control pretty basic stuff like the pitch of my oscillators and the cutoff on my filter.
Where I started to digress from the original circuit is - I hooked the LFOs into a 3PDT switch that I've wired in a way so it would give me: 1.) 2 separate LFOs or 2.) Bleed the voltage from LFO 1 into LFO 2 to get some real wonky wave shapes. They're all hooked up to 5K pots (would have been 1K like on schematic, but Thonk didn't have any 1K 9mm metal-shaft pots in stock) to adjust the amplitude(?) of the signal going into each LED and another 5K pot hooked up the the 3PDT switch to adjust the blend of the 2 LFOs.
If anyone's interested in how I've wired up the switch I'd be happy to share, but I'd suggest trying to use your noggin and figure out the wiring yourself. I love figuring out the wiring of switches myself. I find them a bit like a puzzle, so it's really rewarding when I finally figure it out.
Edit (Sep 6, 2018): I can't for the life of me find the thread where someone has posted a tried and tested modification to this circuit for a wider frequency range. What a bummer. I did, however, find a little forum from 2004 on diystompboxes.com where a few salty users accuse Colin (experimentalistsanonymous) of unjustly putting his name on the above schematic. Have a read here. Yeesh...
It made me think though. I'm pretty sure the 1µF capacitor is there as part of the integrator circuit which basically shapes the square wave signal into a triangle wave signal, so changing that would have no effect over the frequency range. What I'm starting to think is that you'd need to change the 47µF capacitor for that. The penny kinda dropped when I realised that Colin had already put the formula for the circuit right at the top of the schematic. In red too, mind you. Don't know how I missed that.
I mocked up a spreadsheet of the formula so I could change the values of the capacitor and resistor on the fly, but the numbers it was spitting out didn't really look quite right to be honest. Also, I'm not an EE and have really only been reading up on this kind of stuff for the past 5 or 6 months.
My gut feeling is that if the value of the capacitor is lowered and the value of the potentiometer is raised then the maximum speed will be higher (due to the capacitor charging and discharging more frequently) and the frequency range would be wider due to the wider resistance range on the larger pot. Makes sense, yah?
I'll try this out one day, but it wasn't really useful to me to have a faster frequency right now. My current circuit is powering vactrols, which aren't super responsive to really quick changes in light.
