How to increase sampling rate on MCP3008 in python

Question

I am trying to push the MCP3008 to its limits and sample as many samples as possible from a single channel per second. I am also not trying to have to write any C or assembly code, and keep it all as much as possible in python.

My approach so far has been rather naive, I imported python libraries which instantiate SPI and MCP3008 classes, so my python can read from the MCP3008. All I did was call the function set_clock_hz to the max when I instantiated the class. The idea was that I can max out the clock on the MCP and sample as high a frequency as possible

Below is my code.

# Simple example of reading the MCP3008 analog input channels and printing
# them all out.
import time
# Import SPI library (for hardware SPI) and MCP3008 library.
import Adafruit_GPIO.SPI as SPI
import Adafruit_MCP3008
import csv
# Software SPI configuration:
#CLK  = 18
#MISO = 23
#MOSI = 24
#CS   = 25
#mcp = Adafruit_MCP3008.MCP3008(clk=CLK, cs=CS, miso=MISO, mosi=MOSI)

# Hardware SPI configuration:
SPI_PORT   = 0
SPI_DEVICE = 0
mcp = Adafruit_MCP3008.MCP3008(spi=SPI.SpiDev(SPI_PORT, SPI_DEVICE, 50000)) #50000 max speed in hz


print('Reading MCP3008 values, press Ctrl-C to quit...')
# Print nice channel column headers.

# Main program loop.

#Run for one second
t_end = time.time() + 1
arr = []

while time.time() < t_end:  
# The read_adc function will get the value of the specified channel (0-7).
    value = mcp.read_adc(7)
    arr.append(value)

#Write results
with open('highFreqMeas.csv', "w") as output:
    writer = csv.writer(output, delimiter=",", lineterminator='\n')
    for i in arr:
        writer.writerow([i])

#Read results to see how many samples in second
with open('highFreqMeas.csv', "r") as infile:
    reader = csv.reader(infile, delimiter=",", lineterminator='\n')
    reader = list(reader)
    print len(reader)

Answer 1

It's not clear if you are bit banging SPI or not (i.e. using software SPI). If you are then stop doing that and use hardware SPI via the Python spidev module.

You have the constant 50000 in your code. That is no where near the maximum SPI bit rate for the MCP3008. The datasheet suggests it can always support at least 1.35 MHz for SPI, i.e. 1350000 bits per second.