python script to continuously sample ADC connected to raspberry pi via I2C

adcpi18.py

#!/usr/bin/env python
# read abelectronics ADC Pi V2 board inputs with repeating reading from each channel.
# # Requries Python 2.7
# Requires SMBus 
# I2C API depends on I2C support in the kernel

# Version 1.0  - 06/02/2013
# Version History:
# 1.0 - Initial Release

#
# Usage: changechannel(address, hexvalue) to change to new channel on adc chips
# Usage: getadcreading(address, hexvalue) to return value in volts from selected channel.
#
# address = adc_address1 or adc_address2 - Hex address of I2C chips as configured by board header pins.

from smbus import SMBus
import re

adc_address1 = 0x68
adc_address2 = 0x69

# create byte array and fill with initial values to define size
adcreading = bytearray()

adcreading.append(0x00)
adcreading.append(0x00)
adcreading.append(0x00)
adcreading.append(0x00)


# LSB = 15.625 * 10**(-6) # uV
# LSB = 62.5 * 10**(-6) # uV
Vref = 2.048
LSB = (2 * Vref) / 2**12

# voltage_divider = (9.99 / (9.99 + 6.8))
voltage_divider = (6.8 / (9.99 + 6.8))

# detect i2C port number and assign to i2c_bus
# for line in open('/proc/cpuinfo').readlines():
#     m = re.match('(.*?)\s*:\s*(.*)', line)
#     if m:
#         (name, value) = (m.group(1), m.group(2))
#         if name == "Revision":
#             if value [-4:] in ('0002', '0003'):
#                 i2c_bus = 0
#             else:
#                 i2c_bus = 1
#             break
               
shunt_r = 54.7
bus = SMBus(1)
 
def changechannel(address, adcConfig):
  tmp= bus.write_byte(address, adcConfig)

def quickadcreading(address, adcConfig):
  adcreading = bus.read_i2c_block_data(address,adcConfig)
  h = adcreading[0]
  m = adcreading[1]
  s = adcreading[2]
  
  # shift bits to product result
  t = ((h & 0b00111111) << 8) | (m) 
  # check if positive or negative number and invert if needed
  if (h > 0b01000000):
    t = ~(0x004000 - t)
  return t 

def getadcreading(address, adcConfig):
  adcreading = bus.read_i2c_block_data(address,adcConfig)
  h = adcreading[0]
  m = adcreading[1]
  s = adcreading[2]
  # wait for new data
  while (s & 128):
    adcreading = bus.read_i2c_block_data(address,adcConfig)
    h = adcreading[0]
    m = adcreading[1]
    s = adcreading[2]
  
  # shift bits to product result
  t = ((h & 0b00111111) << 8) | (m) 
  # check if positive or negative number and invert if needed
  if (h > 0b01000000):
    t = ~(0x004000 - t)
  return t 
  
while True:
  v = getadcreading(adc_address1,0xB0) * LSB / voltage_divider
  # getadcreading(adc_address1, 0x93)
  for i in range(60):
    shunt_v = getadcreading(adc_address1,0x93) * LSB/8
    shunt_i = shunt_v / shunt_r
    #print ("Channel 1: %0.2fuA, %0.2fuW, %0.2fV, %0.2fmV" % (shunt_i * 10**6, shunt_i*v* 10**6, v, shunt_v * 10**3))
    my_i = (shunt_i * 10**6)
    print (("%7.2fuA: " % (my_i)) + ("-" * int(my_i/ 14)))