mcp3204.py

#!/usr/bin/python
#
#       MCP3204/MCP3208 sample program for Raspberry Pi
#
#       how to setup /dev/spidev?.?
#               $ suod modprobe spi_bcm2708
#
#       how to setup spidev
#               $ sudo apt-get install python-dev python-pip
#               $ sudo pip install spidev
#
import spidev
import time

class MCP3208:
        def __init__(self, spi_channel=0):
                self.spi_channel = spi_channel
                self.conn = spidev.SpiDev(0, spi_channel)
                self.conn.max_speed_hz = 1000000 # 1MHz

        def __del__( self ):
                self.close

        def close(self):
                if self.conn != None:
                        self.conn.close
                        self.conn = None

        def bitstring(self, n):
                s = bin(n)[2:]
                return '0'*(8-len(s)) + s

        def read(self, adc_channel=0):
                # build command
                cmd  = 128 # start bit
                cmd +=  64 # single end / diff
                if adc_channel % 2 == 1:
                        cmd += 8
                if (adc_channel/2) % 2 == 1:
                        cmd += 16
                if (adc_channel/4) % 2 == 1:
                        cmd += 32

                # send & receive data
                reply_bytes = self.conn.xfer2([cmd, 0, 0, 0])

                #
                reply_bitstring = ''.join(self.bitstring(n) for n in reply_bytes)
                # print reply_bitstring

                # see also... http://akizukidenshi.com/download/MCP3204.pdf (page.20)
                reply = reply_bitstring[5:19]
                return int(reply, 2)

if __name__ == '__main__':
        spi = MCP3208(0)

        count = 0
        a0 = 0
        a1 = 0
        a2 = 0
        a3 = 0

        while True:
                count += 1
                a0 += spi.read(0)
                a1 += spi.read(1)
                a2 += spi.read(2)
                a3 += spi.read(3)

                if count == 10:
                        print "ch0=%04d, ch1=%04d, ch2=%04d, ch3=%04d" % (a0/10, a1/10, a2/10, a3/10)
                        count = 0
                        a0 = 0
                        a1 = 0
                        a2 = 0
                        a3 = 0

How exactly do you wire the MCP3208 to the Raspberry Pi if you are running this code? Specifically, I'm wondering about the CS, DIN, DOUT, and CLK pins?

Do you know how exactly one should wire it?

I think there's a bug in 52 line. In my mind there should be " reply = reply_bitstring[7:19] " because mcp320[2/4/8] is 12-bit resolution not 14-bit.

Thank you very much! That helped me kickstart development. I introduced a dedicated function for averaging:

	def readAverage(self, adc_channel=0, nAverage=128, bDebug=0):
		raw = 0
		for i in range(nAverage):
			raw += self.read(adc_channel)
		fMean = raw / nAverage

		if bDebug:
			print('nAverage={:d}: mean value={:7.2f}ticks'.format(nAverage, fMean))
		return fMean

The main function then reads

if __name__ == '__main__':
	spi = MCP3208(spi_channel=0)

	while True:
		a0 = spi.readAverage(0, nAverage=256)
		a1 = spi.readAverage(1)
		a2 = spi.readAverage(2)
		a3 = spi.readAverage(3)

		print('rawValues: {:7.2f} {:7.2f} {:7.2f} {:7.2f}'.format(a0, a1, a2, a3))
		#time.sleep(0.5)

how the mode 0,0 or mode 1,1 is selected ?