analogread.py

# Written by Limor "Ladyada" Fried for Adafruit Industries, (c) 2015
# This code is released into the public domain

import time
import os
import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BCM)
DEBUG = 1

# 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)
# To LEDs SPI Interface ADC Chip: MCP3008 Potentiometer
        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
		
# change these as desired - they're the pins connected from the
# SPI port on the ADC to the Cobbler
SPICLK = 18
SPIMISO = 23
SPIMOSI = 24
SPICS = 25

# set up the SPI interface pins
GPIO.setup(SPIMOSI, GPIO.OUT)
GPIO.setup(SPIMISO, GPIO.IN)
GPIO.setup(SPICLK, GPIO.OUT)
GPIO.setup(SPICS, GPIO.OUT)

LED1 = 12
LED2 = 16
LED3 = 20
LED4 = 21

# set up the SPI interface pins
GPIO.setup(LED1, GPIO.OUT)
GPIO.setup(LED2, GPIO.OUT)
GPIO.setup(LED3, GPIO.OUT)
GPIO.setup(LED4, GPIO.OUT)

# 10k trim pot connected to adc channel #0
potentiometer_adc = 0;


while True:
        # read the analog pin
        trim_pot = readadc(potentiometer_adc, SPICLK, SPIMOSI, SPIMISO, SPICS)
 
        if DEBUG:
                print "trim_pot:", trim_pot
        if ( trim_pot > 0 ):
                GPIO.output(LED1, True)
        else:
                GPIO.output(LED1, False)
        if ( trim_pot > 64 ):
                GPIO.output(LED2, True)
        else:
                GPIO.output(LED2, False)
        if ( trim_pot > 128 ):
                GPIO.output(LED3, True)
        else:
                GPIO.output(LED3, False)
        if ( trim_pot > 192 ):
                GPIO.output(LED4, True)
        else:
                GPIO.output(LED4, False)
        # hang out and do nothing for a half second
        time.sleep(0.5)