mcp3002.py

import spidev

# credits to http://raspberry.io/projects/view/reading-from-a-mcp3002-analog-to-digital-converter/
# modified by Ramzi Sabra

class MCP3002:

    def __init__(self, device=0):
        self.conn = spidev.SpiDev(0, device)
        self.conn.max_speed_hz = 1200000 # 1.2 MHz

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

    def read(self, channel=0):
        cmd = 128
        if channel:
            cmd += 32
        reply_bytes = self.conn.xfer2([cmd, 0])
        reply_bitstring = ''.join(MCP3002.bitstring(n) for n in reply_bytes)
        reply = reply_bitstring[5:15]
        return int(reply, 2) / 2**10

test.py

import time
import mcp3002

adc = mcp3002.MCP3002(device=0)
while True:
    read_value = adc.read(channel=0)
    real_value = 1 - read_value
    percentage_value = real_value * 100
    print("{:3f}%".format(percentage_value))
    time.sleep(0.1)