Digital Music Programming II: RC timing of variable resistance



This lab demonstrates how to measure variable resistance from Force Sensing Resistors (or other sensors related to potentiometers) with a Resistor-Capacitor timing circuit. The measured resistance data can then be sent to the computer as MIDI continuous controller data.

rcfsr.bsx 
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fcount      con  1            
timevar     var  word         
scaledval   var  byte         
tempval     var  word         
channel     var  byte         
fdata       var  byte(fcount) 
lastnote    var  byte(fcount) 
midioutpin con   15           
midirate   con   60

gosub initialize       

top:
   for channel = 0 to fcount - 1
      gosub readFsrSensor
      gosub processSensorValue
      pause 100
   next
   goto top

readFsrSensor:
   high channel
   pause 1            
   rctime channel, 1, timevar
return

processSensorValue:
   gosub scaleTiming
   if (scaledval = fdata(channel)) then endProcessTiming
      fdata(channel) = scaledval
      gosub sendMidiData
   endProcessTiming:
return

scaleTiming:
   tempval = (65535 - timevar + 1) / 256
   if (tempval > 128) then nextline2
      tempval = 0;
      goto nextline3
   nextline2:
   tempval = tempval - 128
   nextline3:
   if (tempval < 128) then nextline
      tempval = 127
   nextline:
   scaledval = tempval
return

initialize:
   for channel = 0 to fcount - 1
      gosub readFsrSensor
      gosub scaleTiming
      fdata(channel) = scaledval
      lastnote(channel)  = 0          
   next
return

sendMidiData:
   if (fdata(channel) = 0) then sendMidiDataEnd
   serout midioutpin, midirate, [$90, lastnote(channel), 0]
   serout midioutpin, midirate, [$90, fdata(channel), 64]
   lastnote(channel) = fdata(channel)
   sendMidiDataEnd:
return