October 2013 - esologic

Turns out it’s not that hard at all! Here’s a video of the whole thing working:

This basically works around concepts I first explained here. It’s still really cool though! SPI is really fast and really easy to use, perfect for a novice like me.

Here are the physical representations and schematics of the setup seen on my desk:

Images generated by fritzing.

Here’s the code that makes it all work!

#first ADC setup on SPI port 0
import spidev
spi_0 = spidev.SpiDev()
spi_0.open(0, 0)

#this fucntion can be used to find out the ADC value on ADC 0
def readadc_0(adcnum_0):
    if adcnum_0 > 7 or adcnum_0 < 0:
        return -1
    r_0 = spi_0.xfer2([1, 8 + adcnum_0 << 4, 0])
    adcout_0 = ((r_0[1] & 3) << 8) + r_0[2]
    return adcout_0

#first ADC setup on SPI port 1
import spidev
spi_1 = spidev.SpiDev()
spi_1.open(0, 1)

#this fucntion can be used to find out the ADC value on ADC 1
def readadc_1(adcnum_1):
    if adcnum_1 > 7 or adcnum_1 < 0:
        return -1
    r_1 = spi_1.xfer2([1, 8 + adcnum_1 << 4, 0])
    adcout_1 = ((r_1[1] & 3) << 8) + r_1[2]
    return adcout_1

while 1:
	for x in range (0, 8):
		print 'Port ' + str(x) + ' | '  + 'adc_0: ' + str(readadc_0(x)).zfill(4) + ' | ' + 'adc_1: ' + str(readadc_1(x)).zfill(4)
	print '----------------------------------'

#first ADC setup on SPI port 0

import spidev

spi_0 = spidev.SpiDev()

spi_0.open(0, 0)

#this fucntion can be used to find out the ADC value on ADC 0

def readadc_0(adcnum_0):

if adcnum_0 > 7 or adcnum_0 < 0:

return -1

r_0 = spi_0.xfer2([1, 8 + adcnum_0 << 4, 0])

adcout_0 = ((r_0[1] & 3) << 8) + r_0[2]

return adcout_0

#first ADC setup on SPI port 1

import spidev

spi_1 = spidev.SpiDev()

spi_1.open(0, 1)

#this fucntion can be used to find out the ADC value on ADC 1

def readadc_1(adcnum_1):

if adcnum_1 > 7 or adcnum_1 < 0:

return -1

r_1 = spi_1.xfer2([1, 8 + adcnum_1 << 4, 0])

adcout_1 = ((r_1[1] & 3) << 8) + r_1[2]

return adcout_1

while 1:

for x in range (0, 8):

print 'Port ' + str(x) + ' | ' + 'adc_0: ' + str(readadc_0(x)).zfill(4) + ' | ' + 'adc_1: ' + str(readadc_1(x)).zfill(4)

print '----------------------------------'

Here is some further reading:

http://www.megaleecher.net/sites/default/files/images/raspberry-pi-rev2-gpio-pinout.jpg

http://hertaville.com/2013/07/24/interfacing-an-spi-adc-mcp3008-chip-to-the-raspberry-pi-using-c/

http://tightdev.net/SpiDev_Doc.pdf

Thanks for reading!

Hey! This post was written a long time ago, but I'm leaving it up on the off-chance it may help someone. Proceed with caution. It may not be a good idea to blindly integrate this code or work into your project, but instead use it as a starting point.

esologic

Month: October 2013

Accessing both SPI ports on the raspberry pi using python