Update 'Future Modules'

Future-Modules.md

@@ -24,6 +24,11 @@ Pretty confident we do these in this order next.
 # More distant future
 Less confident about the order or selection of these, though we do know we need a noise and envelope generator and a S&H would be nice.
 
+## LFO
+Lots of options for this one, but many people have at least two LFOs anyway.
+
+
+
 ## Sample & Hold
 #### MK's S&H, though maybe move the noise generator to a separate module?  If possible?
 * full unit is ~$8.50 - $10 in parts, mostly down to PCB for holding three chips (two 74s, one 72)
@@ -49,3 +54,13 @@ Less confident about the order or selection of these, though we do know we need
 * third iteration of a simple manual EG
 * ~$7 in parts, depending mainly on whether 8+6 pins + hardware fits on shaek board or similar size perf.
 
+## Moar VCOs
+Tons of these, too, and most people want at least two of these in a rack, if not a half dozen.
+
+#### Reverse Avalanche VCO
+* See http://www.kerrywong.com/2014/03/19/bjt-in-reverse-avalanche-mode/ for the principle
+* https://www.lookmumnocomputer.com/simplest-oscillator/ for a drone / manual version, 
+* https://kassu2000.blogspot.com/2018/07/avalance-vco.html for a VC version.
+** not a very large range of in-tune response, but comments discuss potential fixes, maybe worth it for practice
+** about $3 in parts (no ICs), and a big part of that is PCB and IDC, so expanding to a dual or quad would add very little cost
+** cheap way to get to a slightly-detuned supersaw, with a voltage splitter or multiplexer module