MAX7219

Python PC Printer Port MAX7219 LED Display Serial ADC Interface

by Lewis Loflin

This program shows how to connect a MAX7219 8-digit LED display to the IBM PC printer port. This program converts an integer to binary coded decimal (BCD) the displays the count on the right four digits of the 8-digit, 7-segment LED display.

Here we read the serial data from a TLC548 analog to digital converter.

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

Here I've used generic MAX7219 modules from Ebay and wire them as shown above.

View DB25 Printer port connector.

TLC548 ADC pinout

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

8-digit MAX7219

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 pportlcdADC.py
# http://www.bristolwatch.com/pport/index.htm
# By Lewis Loflin - lewis@bvu.net
# Must use my version of pyparallel on website for p.data().

# This combines two earlier modules
# pport7219.py and pporttlc548bits.py
# Programs reads value from ADC and 
# displays 8-digit LED display.


import parallel
import time

p = parallel.Parallel()


# init i/o pins
p.setDataStrobe(0) # Pin 1 use as CLK on MAX7219 LOW to HIGH to LOW
p.setAutoFeed(0)   # Pin 14 use as data bit
p.getInError()	   # Pin 15 Input NC
p.setInitOut(1)    # pin 16 NC
p.setSelect(0)     # pin 17 CS connect to 
				   # LD pin on MAX7219 LOW to HIGH to LOW


# clock bit into MAX7219
def pulseCLK():
    p.setDataStrobe(1)
   # time.sleep(.01) 
    p.setDataStrobe(0)
    return

# clock data-location into MAX7219
def pulseCS():
    p.setSelect(1)
   # time.sleep(.01)
    p.setSelect(0)
    return

# shift byte into MAX7219
# MSB out first!
def ssrOut(value):
    for  x in range(0,8):
        temp = value & 0x80
        if temp == 0x80:
           p.setAutoFeed(1) # set data bit HIGH
        else:
            p.setAutoFeed(0)
        pulseCLK()
        value = value << 0x01 # shift left
        time.sleep(.001)
    p.setDataStrobe(0)
    p.setAutoFeed(0)
    return 



# convert an 8-bit number to a binary string
def convBinary(value):
    binaryValue = 'b'
    for  x in range(0,8):
        temp = value & 0x80
        if temp == 0x80:
           binaryValue = binaryValue + '1'
        else:
            binaryValue = binaryValue + '0'
        value = value << 1
    return binaryValue

# initialize MAX7219 8 digits BCD
def initMAX7219():
    
    # set decode mode
    ssrOut(0x09) # address
    #	ssrOut(0x00); // no decode
    ssrOut(0xFF) # 4-bit BCD decode eight digits
    pulseCS();

    # set intensity
    ssrOut(0x0A) # address
    ssrOut(0x0D) # 5/32s
    pulseCS()

    # set scan limit 0-7
    ssrOut(0x0B); # address
    # ssrOut(0x07) # 8 digits
    ssrOut(0x03) # 4 digits
    pulseCS()


    # set for normal operation
    ssrOut(0x0C) # address
    # ssrOut(0x00); // Off
    ssrOut(0x01)  # On
    pulseCS()

    for x in range(0,9):
        ssrOut(x)
        ssrOut(0)
        pulseCS()
    return

def writeMAX7219(data, location):
    ssrOut(location)
    ssrOut(data)
    pulseCS()
    return

'''
; 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
'''


# see pporttlc548bits.py

# Connect to TLC548 CLK pin 7 to DB25 pin 2
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
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

initMAX7219() # setup MAX7419


while 1:
    j = readADC()
    # get 1st digit j
    digit = j % 10
    writeMAX7219(digit, 1)
    j = j / 10
    
    digit = j % 10
    writeMAX7219(digit, 2)
    j = j / 10  

    digit = j % 10
    writeMAX7219(digit, 3)
    j = j / 10

    digit = j % 10
    writeMAX7219(digit, 4)
    j = j / 10

    time.sleep(.2)

exit



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Projects


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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.

 


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