SpiConnector.py

#!/usr/bin/env python

import RPi.GPIO as GPIO


# read SPI data from MCP3008 chip, 8 possible adc's (0 thru 7)
def readadc(adcnum, clockpin, mosipin, misopin, cspin):
    if (adcnum > 7) or (adcnum < 0):
        return -1
    GPIO.output(cspin, True)

    GPIO.output(clockpin, False)  # start clock low
    GPIO.output(cspin, False)  # bring CS low

    commandout = adcnum
    commandout |= 0x18  # start bit + single-ended bit
    commandout <<= 3  # we only need to send 5 bits here
    for i in range(5):
        if commandout & 0x80:
            GPIO.output(mosipin, True)
        else:
            GPIO.output(mosipin, False)
        commandout <<= 1
        GPIO.output(clockpin, True)
        GPIO.output(clockpin, False)

    adcout = 0
    # read in one empty bit, one null bit and 10 ADC bits
    for i in range(12):
        GPIO.output(clockpin, True)
        GPIO.output(clockpin, False)
        adcout <<= 1
        if GPIO.input(misopin):
            adcout |= 0x1

    GPIO.output(cspin, True)

    adcout >>= 1  # first bit is 'null' so drop it
    return adcout