Reading an Analog Voltage Through the PC Printer Port Part 2

by Lewis Loflin

Here we simply altered the electrical connections for two of the pins in the TLC548 ADC to free up pins to connect a serial LCD display. This also demonstrates how to manipulate individual bits on the 8-bit data port.

See Reading an Analog Voltage Through the PC Printer Port Part 1

Connect the ADC as follows:

# Connect to TLC548 CS-NOT pin 5 to Db25 pin 3 D1
# Connect to TLC548 CLK pin 7 to Db25 pin 2 D0
# Connect TLC548 Pin 6 DATA OUT to Db25 pin 15

The program is written in Python and runs under Linux. To use this one must setup a module pyparallel. How to set this up is on my webpage Programming the PC Printer Port in Python


#!/usr/bin/env python
# File pporttlc548bits.py
# http://www.bristolwatch.com/pport/index.htm
# By Lewis Loflin - lewis@bvu.net
# Read serial ADC TLC548 and send value to terminal. 
# Connecting the TLC548 to the data port pins D0 and D1.
# Program halts when Sw1 is pressed.
# Sw1 is connected from ground to Db25 pin 10 and pulled high
# by a 10k resistor.

# Because two individual port bites used to control ADC
# they can't be used to display binary.
# This frees up pins 1 and 16 for use with LCD circuit
# with pportlcdADC.py

                              
import parallel
import time

p = parallel.Parallel()

'''
; Pins on the TLC548 8-bit ADC:
; 1 -> Ref + -> connect to Vcc
; 2 -> analog in
; 3 -> Ref - -> connect to GND
; 4 -> GND
; 5 -> CS-NOT -> chip select active LOW
; 6 -> DATA OUT
; 7 -> CLK
; 8 -> Vcc
'''

# init i/o pins
p.setDataStrobe(0) # Pin 1 output NC
p.setAutoFeed(0)   # Pin 14 output NC
p.getInError()	   # Pin 15 input to DATA OUT TLC548
p.setInitOut(1)    # Pin 16 output NC
p.setSelect(0)     # Pin 17 output NC


# Connect to TLC548 CLK pin 7 to Db25 pin 2 D0
def writeD0(bit_val):
    if bit_val == 1:
        p.setData(p.data() | 1) # set bit 0
    else: # clear bit 0
        p.setData(p.data() & (255 - 1))
    return

writeD0(0) # set TLC548 CLK pin 7 LOW

# Connect to TLC548 CS-NOT pin 5 to Db25 pin 3 D1
def writeD1(bit_val):
    if bit_val == 1:
        p.setData(p.data() | 2) #set bit 1
    else: # clear bit 1
        p.setData(p.data() & (255 - 2))
    return

writeD1(1) # set TLC548 CS-NOT pin 5 HIGH 

# data LSB first
# enable TLC548 CS-NOT LOW
# set CLK HIGH
# read data bit shift left
# set CLK LOW


def readADC():
        temp = 0
        writeD1(0) # enable CS-NOT LOW
        # time.sleep(.01)
        for i in range(0,7): # loop here 7 times
                writeD0(1) # CLK HIGH
                temp = temp + p.getInError() # get bit
                temp = temp << 1 # shift 1 bit left
                writeD0(0) # CLK LOW
        writeD0(1) # CLK HIGH
        temp = temp + p.getInError() # get bit 8 
        writeD0(0) # CLK LOW
        writeD1(1) # CS-NOT HIGH 
        return temp


# convert a 8-bit number (integer) to a binary. 
# Returns string.
# unlike python bin() this doesn't drop leading zeros
def convBinary(value):
    binaryValue = 'b'
    for  x in range(0, 8):
        temp = value & 0x80
        if temp == 0x80:
           binaryValue += '1'
        else:
            binaryValue += '0'
        value = value << 1
    return binaryValue
    

def Sw1():
	return p.getInAcknowledge()  
	# check pin 10 Db25 when pressed returns 0

# Sw1 is connected from ground to Db25 pin 10 and pulled high
# by a 10k resistor.
# When Sw1 pressed program exits.	
while Sw1():
        val = readADC()
        time.sleep(.1)
        print "Reading =", convBinary(val), " ", hex(val)
 
        
p.setData(0) # LEDs off

print
print "Exit now."      
        
exit

Projects

Below are listed a series of projects using pyparallel and electronics. Starting with routines I wrote to aid students I'd advise walking through this in sequence. Have fun and send comments and/or corrections to lewis@bvu.net.

Arduino sketches needed by programs:
pportArduino1.ino read only after reset.
pportArduino2.ino reset once and multiple reads.
pportArduino3.ino reset once read write Arduino infinite times - multiple commands.

Related Raspberry Pi projects:
Connect Serial LCD to Raspberry Pi
Serial Read from Arduino to Raspberry Pi
Arduino Raspberry Pi Interface with LCD Display

Linux Videos

Live Linux Distro for Using Printer Port with Electronics
Using the powerful Rox-Filer system in Linux
Use FEH under Linux for a Wallpaper Setter
How to create Symbolic links in Linux

Printer Port Interfacing Videos:
Connect Electronics to PC printer Port with Python
Setup PC Printer Port with Python-Linux
Use PC Printer Port to Read Analog Voltage

Read-Write Arduino ADC PWN with Printer Port
Printer Port to Serial LCD Display
Connect Arduino to PC Printer Port for advanced control

Reading an Analog Voltage Through the PC Printer Port Part 2

Projects

Linux Videos

Printer Port in C