ad-example.py

#!/usr/bin/python
# -*- coding: utf-8 -*-
"""PiPyADC: Example file for class ADS1256 in module pipyadc:

ADS1256 cycling through eight input channels.

Hardware: Waveshare ADS1256 board interfaced to the Raspberry Pi 3

Ulrich Lukas 2017-03-10
"""
import sys
import os
import pigpio as io
from ADS1256_definitions import *
from ADS1256_PiGPIO import ADS1256

# Change this to the local DNS name of your Pi (often raspberrypi.local, if you have changed it) or
# make it blank to connect to localhost.
PI_HOST = 'klabs.local'

# if not os.path.exists("/dev/spidev0.1"):
#     raise IOError("Error: No SPI device. Check settings in /boot/config.txt")

### START EXAMPLE ###
################################################################################
###  STEP 0: CONFIGURE CHANNELS AND USE DEFAULT OPTIONS FROM CONFIG FILE: ###
#
# For channel code values (bitmask) definitions, see ADS1256_definitions.py.
# The values representing the negative and positive input pins connected to
# the ADS1256 hardware multiplexer must be bitwise OR-ed to form eight-bit
# values, which will later be sent to the ADS1256 MUX register. The register
# can be explicitly read and set via ADS1256.mux property, but here we define
# a list of differential channels to be input to the ADS1256.read_sequence()
# method which reads all of them one after another.
#
# ==> Each channel in this context represents a differential pair of physical
# input pins of the ADS1256 input multiplexer.
#
# ==> For single-ended measurements, simply select AINCOM as the negative input.
#
# AINCOM does not have to be connected to AGND (0V), but it is if the jumper
# on the Waveshare board is set.
#
# Input pin for the potentiometer on the Waveshare Precision ADC board:
POTI = POS_AIN0|NEG_AINCOM
# Light dependant resistor of the same board:
LDR  = POS_AIN1|NEG_AINCOM
# The other external input screw terminals of the Waveshare board:
EXT2, EXT3, EXT4 = POS_AIN2|NEG_AINCOM, POS_AIN3|NEG_AINCOM, POS_AIN4|NEG_AINCOM
EXT5, EXT6, EXT7 = POS_AIN5|NEG_AINCOM, POS_AIN6|NEG_AINCOM, POS_AIN7|NEG_AINCOM

# You can connect any pin as well to the positive as to the negative ADC input.
# The following reads the voltage of the potentiometer with negative polarity.
# The ADC reading should be identical to that of the POTI channel, but negative.
POTI_INVERTED = POS_AINCOM|NEG_AIN0

# For fun, connect both ADC inputs to the same physical input pin.
# The ADC should always read a value close to zero for this.
SHORT_CIRCUIT = POS_AIN0|NEG_AIN0

# Specify here an arbitrary length list (tuple) of arbitrary input channel pair
# eight-bit code values to scan sequentially from index 0 to last.
# Eight channels fit on the screen nicely for this example..
CH_SEQUENCE = (POTI, LDR, EXT2, EXT3, EXT4, EXT7, POTI_INVERTED, SHORT_CIRCUIT)
################################################################################


def do_measurement():
    ### STEP 1: Initialise ADC object using default configuration:
    # (Note1: See ADS1256_default_config.py, see ADS1256 datasheet)
    # (Note2: Input buffer on means limited voltage range 0V...3V for 5V supply)
    ads = ADS1256(pi=io.pi(PI_HOST))

    ### STEP 2: Gain and offset self-calibration:
    ads.cal_self()

    while True:
        ### STEP 3: Get data:
        raw_channels = ads.read_sequence(CH_SEQUENCE)
        voltages     = [i * ads.v_per_digit for i in raw_channels]

        ### STEP 4: DONE. Have fun!
        nice_output(raw_channels, voltages)

### END EXAMPLE ###


#############################################################################
# Format nice looking text output:
def nice_output(digits, volts):
    sys.stdout.write(
          "\0337" # Store cursor position
        +
"""
These are the raw sample values for the channels:
Poti_CH0,  LDR_CH1,     AIN2,     AIN3,     AIN4,     AIN7, Poti NEG, Short 0V
"""
        + ", ".join(["{: 8d}".format(i) for i in digits])
        +
"""

These are the sample values converted to voltage in V for the channels:
Poti_CH0,  LDR_CH1,     AIN2,     AIN3,     AIN4,     AIN7, Poti NEG, Short 0V
"""
        + ", ".join(["{: 8.3f}".format(i) for i in volts])
        + "\n\033[J\0338" # Restore cursor position etc.
    )


# Start data acquisition
try:
    print("\033[2J\033[H") # Clear screen
    print(__doc__)
    print("\nPress CTRL-C to exit.")
    do_measurement()

except (KeyboardInterrupt):
    print("\n"*8 + "User exit.\n")
    sys.exit(0)