def do_start():
  spi.open(0,0)
  ch0 = [0x0c,0x00,0x00]
  a = adc(ch0)
  b = a[1]
  b = b&0b00001111
  c = a[2]

  value = c+256*b
  voltage = value/4096*5
  zeit = millis()
  voltage = round(voltage,2)
  data=[voltage,zeit]


  with open(csvfilesave,"a") as output:
                 writer = csv.writer(output, delimiter=",",lineterminator = 'n')
                 writer.writerow(data)
  root.after(100, do_start)

Exception in Tkinter callback
Traceback (most recent call last):
File "/usr/lib/python3.5/tkinter/__init__.py", line 1562, in __call__
File "/usr/lib/python3.5/tkinter/__init__.py", line 608, in callit
File "/home/pi/Documents/loggerprojekt/gui.py", line 34, in do_start
OSError: [Errno 24] Too many open files