RPi_mcp3008

RPi_mcp3008 is a library to listen to the MCP3008 A/D converter chip with a RPi. This library implements the example communication protocol described in the datasheet.

Communication is made through RPi SPI port using SpiDev

Wiring

Connect the SPI data cables in the tables below. Choose either CE0# or CE1# to connect to CS.

RPi SPI GPIOs

RPi GPIO	Mode
GPIO 07	CE1#
GPIO 08	CE0#
GPIO 09	MISO
GPIO 10	MOSI
GPIO 11	SCLK

MCP3008 Pinout

Pin	Description	Pin	Description
01	CH0	09	Vdd - Supply voltage (2.7V - 5.5V)
02	CH1	10	Vref - Reference voltage
03	CH2	11	AGND - Analog ground
04	CH3	12	CLK - SPI Clock (SCLK)
05	CH4	13	Dout - Data out (MISO)
06	CH5	14	Din - Data in (MOSI)
07	CH6	15	CS - Chip select (CE0# or CE1#)
08	CH7	16	DGND - Digital ground

Please check the Adafruit guide on the MCP3008 for more information about wiring

Usage

RPi_mcp3008 uses the with statement to properly handle the SPI bus cleanup.

import mcp3008
with mcp3008.MCP3008() as adc:
    print(adc.read([mcp3008.CH0])) # prints raw data [CH0]

It's possible instantiate the object normally, but it's necessary to call the close method before terminating the program.

import mcp3008
adc = mcp3008.MCP3008()
print(adc.read([mcp3008.CH0])) # prints raw data [CH0]
adc.close()

The initialization arguments are MCP3008(bus=0, device=0, max_speed_hz=976000) where: MCP3008(X, Y) will open /dev/spidev-X.Y, same as spidev.SpiDev.open(X, Y) Both arguments are optional and have a default value of 0. The default max SPI driver speed is 976 kHz.

Methods

Currently there are two implemented methods:

def read(self, modes, norm=False):
    '''
    Returns the raw value (0 ... 1024) of the reading.
    The modes argument is a list with the modes of operation to be read (e.g.
    [mcp3008.CH0,mcp3008.Df0]).
    norm is a normalization factor, usually Vref.
    '''

def read_all(self, norm=False):
    '''
    Returns a list with the readings of all the modes
    Data Order:
    [DF0, DF1, DF2, DF3, DF4, DF5, DF6, DF7,
     CH0, CH1, CH2, CH3, CH4, CH5, CH6, CH7]
    norm is a normalization factor, usually Vref.
    '''

The modes argument must be a list with at least one of 16 modes listed below
The norm argument is a normalization factor that rescales raw data, usually Vref

Fixed mode

You can also declare the class with a fixed mode, which will make the instance callable and always return the value of the listed modes. Again you can normalize the data with the norm argument when calling the instance.

import mcp3008
with mcp3008.MCP3008.fixed([mcp3008.CH0, mcp3008.DF0]) as adc:
    print(adc())     # prints raw data [CH0, DF0]
    print(adc(5.2))  # prints normalized data [CH0, DF0]

MCP3008 Operation Modes

MCP3008 has 16 different operation modes: It can listen to each of the channels individually Single Ended or in a pseudo-differential mode Differential

Single Ended	Differential
CH0	DF0 (CH0 = IN+; CH1 = IN-)
CH1	DF0 (CH0 = IN-; CH1 = IN+)
CH2	DF0 (CH2 = IN+; CH3 = IN-)
CH3	DF0 (CH2 = IN-; CH3 = IN+)
CH4	DF0 (CH4 = IN+; CH5 = IN-)
CH5	DF0 (CH4 = IN-; CH5 = IN+)
CH6	DF0 (CH6 = IN+; CH7 = IN-)
CH7	DF0 (CH6 = IN-; CH7 = IN+)

Use the table above as the operation mode when calling MCP3008.read(modes) or setting the MCP3008.fixed(modes) mode. (e.g. MCP3008.read([mcp3008.CH0, mcp3008.DF1]))

luxedo/RPi_mcp3008