iC880A Backplane: ADC example script
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""" | |
Example script to read the input voltage, measured by the MCP3425 ADC. | |
Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/22072b.pdf | |
""" | |
# -*- coding: utf-8 -*- | |
from __future__ import print_function, division | |
import time | |
import smbus | |
bus = smbus.SMBus(1) | |
# I2C address | |
DEVICE_ADDRESS = 0x68 | |
# Voltage dividers | |
DIVIDER_R1 = 6800 | |
DIVIDER_R2 = 3600 | |
DIVIDER_R3 = 470 | |
# ADC reference | |
ADC_REF = 2048 # mV | |
# Config register bits | |
BIT_G0 = 0 | |
BIT_G1 = 1 | |
BIT_S0 = 2 | |
BIT_S1 = 3 | |
BIT_OC = 4 | |
BIT_C0 = 5 | |
BIT_C1 = 6 | |
BIT_RDY = 7 | |
# Conversion mode | |
CONVERSION_MODE_ONESHOT = 0 | |
CONVERSION_MODE_CONT = 1 << BIT_OC | |
# Sample rate / accuracy | |
SAMPLE_RATE_240SPS = 0 # 12 bits | |
SAMPLE_RATE_60SPS = 1 << BIT_S0 # 14 bits | |
SAMPLE_RATE_15SPS = 1 << BIT_S1 # 16 bits | |
# PGA gain selection | |
PGA_GAIN_1 = 0 | |
PGA_GAIN_2 = 1 << BIT_G0 | |
PGA_GAIN_4 = 1 << BIT_G1 | |
PGA_GAIN_8 = (1 << BIT_G1) | (1 << BIT_G0) | |
# Start a conversion in one shot mode | |
START_CONVERSION = 1 << BIT_RDY | |
# Write configuration | |
config = START_CONVERSION | CONVERSION_MODE_ONESHOT | SAMPLE_RATE_15SPS | PGA_GAIN_1 | |
print('Writing data: %s' % bin(config)) | |
bus.write_byte(DEVICE_ADDRESS, config) | |
# Wait a bit for the measurement to finish | |
time.sleep(0.15) | |
# Read measurement | |
data = bus.read_i2c_block_data(DEVICE_ADDRESS, 0x00, 3) | |
value = (data[0] << 8) + data[1] | |
# Calculate voltage for the specified bit of accuracy | |
def get_voltage(measurement, bit): | |
v2 = measurement * ADC_REF / (2**bit) | |
total_r = DIVIDER_R1 + DIVIDER_R2 + DIVIDER_R3 | |
return v2 / (DIVIDER_R2 / total_r) * 2 | |
print(list(map(hex, data))) | |
print(list(map(bin, data))) | |
print('Value is %d/%d' % (value, 2**16)) | |
print('Voltage is %.4f V' % (get_voltage(value, 16) / 1000)) |
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