ADC sampling at fixed rate

Comments

• Mike Green Posts: 23,101

  2009-10-24 18:04 edited 2009-10-24 18:04

  8KHz is slow enough so the timing can be done in Spin. Use one of the MCP3208 drivers. I looked at "MCP3208 fast ADC 12 bit 8 channel" which has an "in" method to get a sample. I'd just use WAITCNT to provide a 125us sampling interval.
  

  OBJ adcObj : "MCP3208_fast"
  PUB fillBuffer(bufferSize, bufferAddress, channel, delayTime) | i, waitTime
  '  Fills a supplied buffer with samples from an MCP3208 ADC at regular intervals.
  '  Note that adcObj.start needs to be called before calling this routine.
  '  See the comments in MCP3208_fast for how to call that.
  '
  '  bufferSize is the number of (word) entries in the buffer
  '  bufferAddress is the address of the start of the buffer
  '  channel is the number of the ADC channel to use
  '  delayTime is the time between samples in microseconds
  '
     delayTime *= clkfreq / 1_000_000     ' Convert from microseconds to clock ticks
     waitTime := cnt     ' Get a starting time
     repeat i from 0 to bufferSize-1     ' Repeat for specified number of samples
        waitcnt(waitTime += delayTime)     ' Wait for specified time (first interval is not used)
        word[noparse][[/noparse] bufferAddress ][noparse][[/noparse] i ] := adcObj.in(channel)     ' Read and store a 12 bit sample
  
• Weav Posts: 2

  2009-10-24 22:21 edited 2009-10-24 22:21

  That looks like the thing. Thank you! If I need a sigma-delta DAC I can use a separate object.