read MCP3002 SPI data by python/spidev ref: http://qiita.com/f_nishio/items/4b9723c4e622a51aaeb5

read_adc.py

#!/usr/bin/env python
# Read the analog sensor value via MCP3002.

import spidev
import time
import subprocess

# open SPI device 0.0
spi = spidev.SpiDev()
spi.open(0, 0)

try:
    while True:
        resp = spi.xfer2([0x68, 0x00])
        value = (resp[0] * 256 + resp[1]) & 0x3ff
        print value
        time.sleep(1)
except KeyboardInterrupt:
    spi.close()

read_adc_wp2.py

#!/usr/bin/env python3

import wiringpi2 as wp
import time

# SPI channel (0 or 1)
SPI_CH = 0

# SPI speed (hz)
SPI_SPEED = 1000000

# GPIO number
LED_PIN = 25

# threshold
THRESHOLD = 200

# setup
wp.wiringPiSPISetup (SPI_CH, SPI_SPEED)
wp.wiringPiSetupGpio()
wp.pinMode(LED_PIN, wp.GPIO.OUTPUT)

while True:
    buffer = 0x6800
    buffer = buffer.to_bytes(2,byteorder='big')
    wp.wiringPiSPIDataRW(SPI_CH, buffer)
    value = (buffer[0]*256+buffer[1]) & 0x3ff
    print (value)

    if value > THRESHOLD:
      wp.digitalWrite(LED_PIN, wp.GPIO.HIGH)
      time.sleep(0.2)
      wp.digitalWrite(LED_PIN, wp.GPIO.LOW)
      time.sleep(0.2)

    time.sleep(1)

read_mcp3002.py

#!/usr/bin/env python3
###
### read MCP3002 ADC analog value via RasPi SPI
###

import wiringpi2 as wp
import time

# SPI channle (0 or 1)
SPI_CH = 0

# pin base (above 64)
PIN_BASE=70

# GPIO number
LED_PIN = 25

# threshold
THRESHOLD = 200

# setup
wp.mcp3002Setup (PIN_BASE, SPI_CH)
wp.wiringPiSetupGpio()
wp.pinMode(LED_PIN, wp.GPIO.OUTPUT)

# if a sensor value is over THRESHOLD,
# flash led.
while True:
    value = wp.analogRead(PIN_BASE)
    print (value)

    if value > THRESHOLD:
      wp.digitalWrite(LED_PIN, wp.GPIO.HIGH)
      time.sleep(0.2)
      wp.digitalWrite(LED_PIN, wp.GPIO.LOW)
      time.sleep(0.2)

    time.sleep(1)