mcp3002.py

import spidev

# Enable SPI0.1 for adc
spi = spidev.SpiDev(0, 0)
spi.max_speed_hz = 1200000

# Adc_ch 0/1
def read_adc(adc_ch):
    # Construct SPI message
    #  First bit (Start): Logic high (1)
    #  Second bit (SGL/DIFF): 1 to select single mode
    #  Third bit (ODD/SIGN): Select channel (0 or 1)
    #  Fourth bit (MSFB): 0 for LSB first
    #  Next 12 bits: 0 (don't care)
    msg = 0b11
    msg = ((msg << 1) + adc_ch) << 5
    msg = [msg, 0b00000000]
    reply = spi.xfer2(msg)

    # Construct single integer out of the reply (2 bytes)
    adc = 0
    for n in reply:
        adc = (adc << 8) + n

    # Last bit (0) is not part of ADC value, shift to remove it
    adc = adc >> 1

    # Return 0-1023
    return adc

def close():
    spi.close()