Alright, I have to start off with the fact I'm a n00b. So there's a good chance I'm screwing something up.
I've got an MCP3008 10-bit ADC hooked up to my Raspberry Pi B+ via a Cobbler.
Here are the particulars of my kernel:
pi@raspberrypi ~ $ uname -a
Linux raspberrypi 3.18.11+ #781 PREEMPT Tue Apr 21 18:02:18 BST 2015 armv6l GNU/Linux
I've wired up the default SPI0_SCLK, MISO, MOSI, and CE0_N to the MCP3008. I roughly followed raspberrypi-spy's guidlines, but making appropriate adaptations for the B+ rather than their A.
I enabled SPI via raspi-config and confirm /dev/spidev0.0 and /dev/spidev/0.1 exist. I also ensured I have the spi_bcm2708 driver enabled.
pi@raspberrypi ~ $ ll /dev/spidev0.*
crw-rw---T 1 root spi 153, 1 Jan 1 1970 /dev/spidev0.1
crw-rw---T 1 root spi 153, 0 Jan 1 1970 /dev/spidev0.0
pi@raspberrypi ~ $ lsmod
Module Size Used by
ctr 3993 1
ccm 8238 1
snd_bcm2835 21149 0
snd_pcm 90778 1 snd_bcm2835
snd_seq 61097 0
snd_seq_device 7209 1 snd_seq
snd_timer 23007 2 snd_pcm,snd_seq
snd 66325 5 snd_bcm2835,snd_timer,snd_pcm,snd_seq,snd_seq_device
arc4 1964 2
rt2800usb 18958 0
rt2800lib 81833 1 rt2800usb
rt2x00usb 11926 1 rt2800usb
rt2x00lib 47785 3 rt2x00usb,rt2800lib,rt2800usb
mac80211 552848 3 rt2x00lib,rt2x00usb,rt2800lib
spi_bcm2708 6018 0
i2c_bcm2708 6200 0
cfg80211 462846 2 mac80211,rt2x00lib
crc_ccitt 1612 1 rt2800lib
rfkill 22347 2 cfg80211
uio_pdrv_genirq 3666 0
uio 9897 1 uio_pdrv_genirq
Just to add more information, but /boot/config.txt
pi@raspberrypi ~ $ cat /boot/config.txt
# For more options and information see
# http://www.raspberrypi.org/documentation/configuration/config-txt.md
# Some settings may impact device functionality. See link above for details
# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1
# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
#disable_overscan=1
# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
#overscan_right=16
#overscan_top=16
#overscan_bottom=16
# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=1280
#framebuffer_height=720
# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1
# uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_group=1
#hdmi_mode=1
# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2
# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4
# uncomment for composite PAL
#sdtv_mode=2
#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800
dtparam=spi=on
dtparam=i2c_arm=on
#dtoverlay=spi-bcm2835-overlay
dtoverlay=spi-bcm2708-overlay
I'm using the python py-spidev. I cannot recall where I installed it from, but I did find this in the .egg:
Metadata-Version: 1.1
Name: spidev
Version: 3.0
Summary: Python bindings for Linux SPI access through spidev
Home-page: http://github.com/doceme/py-spidev
Author: Stephen Caudle
Author-email: scaudle@doceme.com
License: GPLv2
Description: Python Spidev
I have nothing connected to the 8 MCP3008's ADC inputs, so I should get something like 0, or close there abouts. My code is pretty easy. I borrowed the ReadChannel function from the aforementioned raspberrypi-spy link. I assume that is fairly robust.
pi@raspberrypi ~ $ cat adctest.py
#!/usr/bin/python
import time
import spidev
# Open SPI bus
spi = spidev.SpiDev()
spi.open(0,0)
####################################################################################
# Function to read SPI data from MCP3008 chip
# Channel must be an integer 0-7
def ReadChannel(channel):
adc = spi.xfer2([1,(8+channel)<<4,0])
data = ((adc[1]&3) << 8) + adc[2]
return data
####################################################################################
fmt= '{0:5d}'
while True:
chans = [0]*8
for t in range(8):
chans[t] = ReadChannel(t)
#time.sleep(0.01)
line = []
for chan in chans:
line.append(fmt.format(chan))
print ' '.join(line)
time.sleep(0.25)
The resultant output is a little perplexing:
pi@raspberrypi ~ $ sudo ./adctest.py
21 30 0 13 7 17 2 0
0 7 0 6 5 17 6 7
41 40 39 49 57 71 87 126
72 54 46 48 53 60 76 110
58 30 13 8 0 0 0 0
0 0 0 3 1 6 0 0
11 7 4 13 16 30 39 68
65 48 48 50 54 64 79 125
73 52 47 47 54 59 73 105
57 42 29 27 24 20 22 21
0 0 0 0 0 0 0 0
0 4 0 4 4 6 3 4
12 11 8 21 24 32 43 80
69 55 48 50 56 67 81 125
73 50 42 46 51 56 72 106
53 34 20 21 18 14 16 7
0 0 0 0 0 0 0 0
1 4 2 5 4 7 3 7
16 16 18 25 34 44 57 94
73 54 48 53 61 65 84 123
69 51 41 44 48 55 68 96
I connected a device to one channel and I get the exact same thing. I reconnected that ADC channel to GND and I get the same sinusoidal behavior. Same issue if I connect a channel to +3.3VDC. I've swapped out the MCP3008 and I get the same response.
The SPI driver on my pi appears to function correctly. I disconnected my circuit, and tied MOSI to MISO and ran the loopback test, mentioned on raspberrypi.org. This appears to work correctly.
I'm completely perplexed. I had this all functioning a few weeks ago. Maybe something in a recent apt-get upgrade broke things. Any adivce would be most helpful.
Thanks a million, ~Rich
