MCP3204 ADC with low sampling rate << 100kSps

Question

I'm trying to read light value from an LED bilking very fast. So I choose TSL12S as a light sensor, and MCP3204 as an ADC. In datasheet, MCP3204 have sampling rate up to 100 kSps when Vdd = 5 V is applied and I have done so.

But when I tested my program, it outputs every 0.04 seconds, 40 milliseconds. That is, it is only 25 outputs per second. What a such slow rate! I'm not expecting 50 or 100 kilo outputs, but just wanting to see more than 1-5 kilo outputs.

A source code is written in Python and described down below:

#!/usr/bin/env python

import time

import pigpio

if __name__ == "__main__":
    spi_ch = 0
    spi_baud = 10000000
    spi_flag = 0b00 # 0, 0: SCLK idles LOW / 1, 1: SCLK idles HIGH

    pi = pigpio.pi()
    h = pi.spi_open(spi_ch, spi_baud, spi_flag)

    mcp_ch = 0;

    byte1 = 0b110 | mcp_ch >> 2
    byte2 = (mcp_ch & 0b11) << 6
    byte3 = 0

    if h >= 0:
        start = time.time()
        time_old = start

        while (time.time() - start) < 5:
            (b, d) = pi.spi_xfer(h, [byte1, byte2, byte3])

            if b == 3:
                reading = (d[1] & 0b00001111) << 8 | d[2]

                time_now = time.time()
                print "%f\t%d\t+%f" % (time_now - start, reading, time_now - time_old)
                time_old = time_now

        pi.spi_close(h)

    pi.stop()

I use pigpio library from here

Is this problem due to limitations of RPi HW, Raspbian OS, Python, library, or my code itself?

Answer 1

As the author of pigpio I would only use the pigpio Python SPI, I2C, and serial functions if you are using pigpio over a network.

The pigpio Python module uses the socket interface to the pigpio daemon.

You should use the Python smbus module if you are running Python on the local Pi.

The pigpio C bit bang functions will be required if you need >10K samples per second.