vfs5

This firmware is a software implementation of VOX vfs5 footswitch, compatible with the VT/VT+ series of guitar amplifiers. it's tested on a VT20+.

Have a look to http://www.whitelamp.com/public/vox_vfs5.html for the analog circuit reverse engineered from the original VOX footswitch.

we generate a PWM on arduino's digital pin 5, setting the port to the highest possible frequency (~60kHz) and apply to it a simple dual pole low-pass filter to convert the PWM signal in a continous analog voltage:

pin5 >------- 1.2KOhm ------ 1.2KOhm ------> out 
	                   |              |
	                  47nF           47nF
	                  _|_            _|_ 
	                  ///            ///

TODO: use 4 input switches for channel selection

TODO: use a led (or two) to signal currently selected bank

WARNING: the voltage provided by the amp drops to 4.25V when arduino is connected... see MAX_OUTV const