MCP3208 ADC function bug found!

It took me 2 hours to find the bug.  I did not understand why even channels OK, but odd do not.  And if I start with odd channels, then opposite is true.  After a couple of guesses, I finally decided to print out the MCP3208 output.  Then I realized that I take for granted that the Question mark bits in return byte one for some reason depends on the first address.

So when I crop off the most significant 3 bits of byte 1, then everything goes well.  

  resultDecimal =  ((resultTripleByte[1] & 0x0f) * (2 ** 8)) + (resultTripleByte[2])

The lesson learned is to respect the question mark bits in MicroChip's datasheet!


pi@raspberrypi ~/fongtoy $ sudo python fongtoy.py

*** Start Program - FongToy v1.26 tlfong01 2013may28 ***


*** Start testing MCP3208 ADC ***

ADC output byte 0 =  00000010
ADC output byte 0 =  00001001
ADC output byte 0 =  11000010
resultDecimal =  2498
Analog voltage at channel number  1  =  2.498
ADC output byte 0 =  11111111
ADC output byte 0 =  11101001
ADC output byte 0 =  11000010
resultDecimal =  2498
Analog voltage at channel number  3  =  2.498
ADC output byte 0 =  11111111
ADC output byte 0 =  11101001
ADC output byte 0 =  11000011
resultDecimal =  2499
Analog voltage at channel number  5  =  2.499

*** Stop testing MCP3208 ***


*** Stop Program ***

# ftadc.py v1.4 tlfong01 2013may27

import spidev

import time

import ftprint

import ftspi

# *****************************************************************************

# Function - TestAdcMcp3208 

# ***************************************************************************** 

def TestMcp3208v03(): # v0.3 tlfong01 2013may28

    ftprint.PrintDoubleSpaceLine("*** Start testing MCP3208 ADC ***")   

    spiChannel = spidev.SpiDev() 

    spiChannel.open(0, 1)  

    SingleEndMode = 0

    DifferentialMode = 1

    SingleEndModeFirstByte = 0x06

    DifferentialModeFirstByte = 0x04

    controlTripleByte = [0x00, 0x00, 0x00]

    resultTripleByte = [0x00, 0x00, 0x00]

    for channelNumber in range(1, 7, 2):

        controlTripleByte[0] = SingleEndModeFirstByte | (channelNumber >> 2)

        controlTripleByte[1] = channelNumber << 6

        controlTripleByte[2] = 0x00 # don't care, actually

        resultTripleByte = spiChannel.xfer2(controlTripleByte) 

ftprint.PrintEightBitPattern("ADC output byte 0 = ", resultTripleByte[0])

ftprint.PrintEightBitPattern("ADC output byte 0 = ", resultTripleByte[1])

        ftprint.PrintEightBitPattern("ADC output byte 0 = ", resultTripleByte[2])

        resultDecimal =  ((resultTripleByte[1] & 0x0f) * (2 ** 8)) + (resultTripleByte[2])

print "resultDecimal = ", resultDecimal

        resultVoltage = (float(resultDecimal) / 4096) * 4.096     

        print "Analog voltage at channel number ", channelNumber, " = ", resultVoltage

    spiChannel.close() 

    ftprint.PrintDoubleSpaceLine("*** Stop testing MCP3208 ***")

def TestMcp3208v02(inputMode, channelNumber): # v0.2 tlfong01 2013may28

    # ftprint.PrintDoubleSpaceLine("*** Start testing MCP3208 ADC ***")   

    spiChannel = spidev.SpiDev() 

    spiChannel.open(0, 1)  

    time.sleep(0.1)

    CommonMode = 0

    DifferentialMode = 1

    SingleEndModeFirstByte = 0x06

    DifferentialModeFirstByte = 0x04

    controlTripleByte = [0x00, 0x00, 0x00]

    resultTripleByte = [0x00, 0x00, 0x00]

    controlTripleByte[0] = SingleEndModeFirstByte | (channelNumber >> 2)

    controlTripleByte[1] = channelNumber << 6

    controlTripleByte[2] = 0x00 # don't care, actually

    resultTripleByte = spiChannel.xfer2(controlTripleByte) 

    # ftprint.PrintEightBitPattern("ADC output byte 0 = ", resultTripleByte[0])

    # ftprint.PrintEightBitPattern("ADC output byte 1 = ", resultTripleByte[1])

    # ftprint.PrintEightBitPattern("ADC output byte 2 = ", resultTripleByte[2])

    resultDecimal =  (resultTripleByte[1] * (2 ** 8)) + (resultTripleByte[2])

    resultVoltage = (float(resultDecimal) / 4096) * 4.096     

    print "Analog voltage at channel number ", channelNumber, " = ", resultVoltage

    resultDecimal =  (resultTripleByte[1] * (2 ** 8)) + (resultTripleByte[2])

    resultVoltage = (float(resultDecimal) / 4096) * 4.096     

    print "Analog voltage at channel number ", channelNumber, " = ", resultVoltage

    

    resultDecimal =  (resultTripleByte[1] * (2 ** 8)) + (resultTripleByte[2])

    resultVoltage = (float(resultDecimal) / 4096) * 4.096     

    print "Analog voltage at channel number ", channelNumber, " = ", resultVoltage

    spiChannel.close() 

    time.sleep(0.1)

    # ftprint.PrintDoubleSpaceLine("*** Stop testing MCP3208 ***")

def TestMcp3208v01(): # v0.1 tlfong01 2013may27

    ftprint.PrintDoubleSpaceLine("*** Start testing MCP3208 ADC ***")   

    spiGuzuntyPi = spidev.SpiDev() 

    spiGuzuntyPi.open(0, 1)  

    controlTripleByteSingleEndChannel0 = [0x06, 0x00, 0x00]

    resultTripleByte = [0x00, 0x00, 0x00]

    resultTripleByte = spiGuzuntyPi.xfer2(controlTripleByteSingleEndChannel0) 

    ftprint.PrintEightBitPattern("ADC output byte 0 = ", resultTripleByte[0])

    ftprint.PrintEightBitPattern("ADC output byte 1 = ", resultTripleByte[1])

    ftprint.PrintEightBitPattern("ADC output byte 2 = ", resultTripleByte[2])

    resultDecimal =  (resultTripleByte[1] * (2 ** 8)) + (resultTripleByte[2])

    resultVoltage = (float(resultDecimal) / 4096) * 4.096 

    

    print "Analog voltage = ", resultVoltage

    spiGuzuntyPi.close() 

    ftprint.PrintDoubleSpaceLine("*** Stop testing MCP3208 ***") 

# *****************************************************************************

# Function - TestAdcMcp3201() 

# Description - 

# Sample call - 

# ***************************************************************************** 

def TestMcp320101(): #v1.3 tlfong01 2013may23

    ftprint.PrintDoubleSpaceLine("*** Start testing MCP3201 ADC ***")   

    spiGuzuntyPi = spidev.SpiDev() 

    spiGuzuntyPi.open(0, 1)  

    DummyDoubleByteList = [0x00, 0x00]

    adcOutputDoubleByteList = [0x55, 0x55]

    adcOutputDoubleByteList = spiGuzuntyPi.xfer2(DummyDoubleByteList) 

    ftprint.PrintEightBitPattern("ADC output byte 1 = ", adcOutputDoubleByteList[0])

    ftprint.PrintEightBitPattern("ADC output byte 2 = ", adcOutputDoubleByteList[1])

    adcDecimalValue = (adcOutputDoubleByteList[1] >> 1) + (adcOutputDoubleByteList[0] * (2 ** 7))

    # adcAnalogVoltage = (float(adcDecimalValue) / 4096) * 4.10 # without half voltage divider

    adcAnalogVoltage = ((float(adcDecimalValue) / 4096) * 4.10) * 2 # with half voltage divider

    

    print "Analog voltage = ", adcAnalogVoltage

    spiGuzuntyPi.close() 

    ftprint.PrintDoubleSpaceLine("*** Stop testing MCP3201 ***") 

# ***************************************************************************** 

# Function - TestAdcMcp3201() 

# Description - 

# Sample call - 

# Sample output -

# *** Start testing MCP3201 ADC ***

# ADC output byte 1 =  00001011

# ADC output byte 2 =  11111111

# Analog voltage   3.07299804687

# *** Stop testing MCP3201 ***

# ***************************************************************************** 

def TestMcp320102(spiChannel):

    ftprint.PrintDoubleSpaceLine("*** Start testing MCP3201 ADC ***")   

    DummyDoubleByteList = [0x00, 0x00]

    adcOutputDoubleByteList = [0x55, 0x55]

    adcOutputDoubleByteList = spiChannel.xfer2(DummyDoubleByteList) 

    ftprint.PrintEightBitPattern("ADC output byte 1 = ", adcOutputDoubleByteList[0])

    ftprint.PrintEightBitPattern("ADC output byte 2 = ", adcOutputDoubleByteList[1])

    adcDecimalValue = (adcOutputDoubleByteList[1] >> 1) + (adcOutputDoubleByteList[0] * (2 ** 7))

    # adcAnalogVoltage = (float(adcDecimalValue) / 4096) * 4.10 # without half voltage divider

    adcAnalogVoltage = ((float(adcDecimalValue) / 4096) * 4.10) * 2 # with half voltage divider

    

    print "Analog voltage = ", adcAnalogVoltage

    ftprint.PrintDoubleSpaceLine("*** Stop testing MCP3201 ***") 

def TestMcp320103(spiChannel, testTime, testCount):

    ftprint.PrintDoubleSpaceLine("*** Start testing MCP3201 ADC ***")   

    for i in range(testCount):

        DummyDoubleByteList = [0x00, 0x00]

        adcOutputDoubleByteList = [0x55, 0x55]

        adcOutputDoubleByteList = spiChannel.xfer2(DummyDoubleByteList) 

time.sleep(testTime)

    ftprint.PrintEightBitPattern("ADC output byte 1 = ", adcOutputDoubleByteList[0])

    ftprint.PrintEightBitPattern("ADC output byte 2 = ", adcOutputDoubleByteList[1])

    adcDecimalValue = (adcOutputDoubleByteList[1] >> 1) + (adcOutputDoubleByteList[0] * (2 ** 7))

    # adcAnalogVoltage = (float(adcDecimalValue) / 4096) * 4.10 # without half voltage divider

    adcAnalogVoltage = ((float(adcDecimalValue) / 4096) * 4.10) * 2 # with half voltage divider

    

    print "Analog voltage = ", adcAnalogVoltage

    ftprint.PrintDoubleSpaceLine("*** Stop testing MCP3201 ***") 

# .END

# fongtoy v1.26 tlfong01 2013may28

ProgramTitle = "FongToy v1.26 tlfong01 2013may28"

import sys 

import time 

import smbus 

import pdb 

import spidev 

import wiringpi

import wiringpi2

import RPIO as GPIO  

from RPIO import PWM 

from enum import Enum 

from subprocess import call

import ftgpio

import ftprint

import ftspi

import ftiox

import fteeprom

import ftguzuntypi

import ftdemux

import fttest

import ftadc

# *** Main program ***

# *** Start program message ***

ftprint.StartProgram(ProgramTitle)

# *** Troubleshooting functions ***

# *** GPIO tests v1.3 tlfong01 2013may23 ***

# ftgpio.TestLed()

# ftgpio.TestBuzzer()

# ftgpio.TestButtonEchoBuzzer()

# ftgpio.TestButtonEchoLed()

# *** SPI Tests v1.3 tlfong01 2013may23 ***

# ftspi.TestSpiLoopBack(spiChannelNumber = 0, spiChipEnableNumber = 1, testDataByte = 0x55, testCount = 1000, testTime = 0.001)

# ftiox.TestMcp23s17BlinkLed(spiChannelNumber = 0, spiChipEnableNumber = 0, spiChipSubAddress = 0)

# fteeprom.TestWriteReadEepormDataByte(spiChannelNumber = 0, spiChipEnableNumber = 1, startAddress = 0x0410, testDataByte = 0x55)

# ftguzuntypi.TestGuzuntyPi4digit7segmentLedModule(spiChannelNumber = 0, spiChipEnableNumber = 1)

# ftdemux.TestSelectSpiSlaveDevice(spiChannelNumber = 0, spiChipEnableNumber = 0, spiIoxSubAddress = 0, spiSlaveDeviceNumber = 5)

# fttest.TestDemuxEeprom(mcp23s17SubAddress = 0, eepromDemuxAddress = 2, testStartAddress = 0x0123, testWriteDataByte = 0x5a)

# fttest.TestDemuxEeprom(mcp23s17SubAddress = 0, eepromDemuxAddress = 1, testStartAddress = 0x0123, testWriteDataByte = 0x3b)

# fttest.TestDemuxEeprom(mcp23s17SubAddress = 0, eepromDemuxAddress = 0, testStartAddress = 0x0123, testWriteDataByte = 0x3b)

# *** Current test functions ***

# ftiox.TestMcp23s17BlinkLed(spiChannelNumber = 0, spiChipEnableNumber = 0, spiChipSubAddress = 0)

# ftdemux.TestSelectSpiSlaveDevice(spiChannelNumber = 0, spiChipEnableNumber = 0, spiIoxSubAddress = 0, spiSlaveDeviceNumber = 5)

# fttest.TestDemuxEeprom(mcp23s17SubAddress = 0, eepromDemuxAddress = 0, testStartAddress = 0x0123, testWriteDataByte = 0x3b)

# fttest.TestDemuxEeprom(mcp23s17SubAddress = 0, eepromDemuxAddress = 1, testStartAddress = 0x0411, testWriteDataByte = 0x4c)

# fttest.TestDemuxGuzuntyClock(mcp23s17SubAddress = 0, guzuntyClockDemuxAddress = 2, secondCount = 10)

# fttest.TestMcp320103(testTime = 0.1, testCount = 10)

# fttest.TestMcp320103(testTime = 0.01, testCount = 100)

# fttest.TestMcp320103(testTime = 0.05, testCount = 50)

# fttest.TestMcp320103(testTime = 0.1, testCount = 1)

# ftspi.TestSpiLoopBackV01(spiChannelNumber = 0, spiChipEnableNumber = 1, testDataByte = 0x55, testTime = 0.001, testCount = 60000)

# ftadc.TestMcp320101()

# ftadc.TestMcp3208v01()

# ftadc.TestMcp3208v02(inputMode = 1, channelNumber = 0) 

ftadc.TestMcp3208v03() 

# *** Stop program message ***

ftprint.StopProgram()

#.END

.END