Arduino Raspberry Pi Interface with LCD Display

by Lewis Loflin

For an explanation on the operation of the LCD part of this page see Connect a Serial LCD Display to Raspberry Pi

For an explanation of how to read 16-bit code from Arduino without the use of I2C see Serial Read from Arduino to Raspberry Pi

The Arduino sketch is arduino_ds18b20X2.ino.

This program is a combination of the above two programs. Arduino operates any number of sensors while Raspberry Pi reads the integer results, does any conversions, and displays the result on a serial LCD display.

The program will reset Arduino and the sensor routines/calls are in the Arduino setup section. The return value is stored in a variable and read back by Raspberry Pi.

Arduino is programmed to operate as a 16-bit TLC548 ADC.

#!/usr/bin/env python
# File rpi_arduino_lcd.py
# use with sketch arduino_ds18b20X2.ino

# http://www.bristolwatch.com/pport/index.htm
# By Lewis Loflin - lewis@bvu.net

# access to GPIO must be through root
import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False) # disable warnings

CS = 18
CLK =23
dataBit = 24
Reset = 25

GPIO.setup(CS, GPIO.OUT) # CS to Arduino DP5
GPIO.setup(CLK, GPIO.OUT) # CLK to Arduino DP6
GPIO.setup(dataBit, GPIO.IN) # dataBit to Arduino DP4
GPIO.setup(Reset, GPIO.OUT) # Reset to Arduino Reset

# Setup IO
GPIO.output(CS, 0)
GPIO.output(CLK, 0)
GPIO.output(Reset, 0)

Line1 = 0x80  # location LCD row 0 col 0 or line 1
Line2 = 0xC0  # location LCD row 1 col 0 or line 2

# Bit_out  Pin 1-2 SN74164 yellow wire
lcdBit = 15 # P3
# CLK  Pin 9 SN74164 - clock bit - LOW to HIGH to LOW orange wire
lcdClk = 23 # SCK
# RS Pin 4 LCD  - LOW command; HIGH ASCII white wire
RS = 16 # P4
# E Pin 6 LCD - clock data into LCD - HIGH to LOW to HIGH brown wire
E = 22 # P6

GPIO.setup(lcdBit, GPIO.OUT) 
GPIO.setup(lcdClk, GPIO.OUT) 
GPIO.setup(RS, GPIO.OUT) 
GPIO.setup(E, GPIO.OUT)

# Setup IO
GPIO.output(lcdBit, 0)
GPIO.output(lcdClk, 0)
GPIO.output(RS, 0)
GPIO.output(E, 1)

def pulseCLK():
    GPIO.output(lcdClk, 1)
   # time.sleep(.01) 
    GPIO.output(lcdClk, 0)
    return

def pulseE():
    GPIO.output(E, 0)
   # time.sleep(.01)
    GPIO.output(E, 1)
    return

# MSB out first!
def ssrWrite(value):
    for  x in range(0,8):
        temp = value & 0x80
        if temp == 0x80:
           GPIO.output(lcdBit, 1) # data bit HIGH
        else:
           GPIO.output(lcdBit, 0) # data bit LOW
        pulseCLK()
        value = value << 0x01 # shift left
        time.sleep(.001)
    GPIO.output(lcdClk, 0)
    GPIO.output(lcdBit, 0)
    return 

def initLCD():
    GPIO.output(RS, 0) # RS LOW
    ssrWrite(0x38) # setup for 2 lines
    pulseE()
    ssrWrite(0x0F) # blinking cursor
    pulseE()
    clearLCD()
    Home()
    return 

def clearLCD():
    GPIO.output(RS, 0) # RS LOW
    ssrWrite(0x01) # clear
    pulseE()
    return
    
def Home():
    GPIO.output(RS, 0) # RS LOW
    ssrWrite(0x02) # home
    pulseE()
    return 

def gotoLocation(val):
    GPIO.output(RS, 0) # RS LOW
    if val < 0x80:
        val = 0x80
    ssrWrite(val)
    pulseE()
    return

def writeString(myString):
    i = len(myString)
    GPIO.output(RS, 1) # RS - HIGH is ASCII
    for  x in range(0,i):
       y = ord(myString[x])
       ssrWrite(y)
       pulseE()
    GPIO.output(RS, 0) # RS LOW
    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

def degC(val):
	return val * 0.0625

def degF(val):
	return (val * 0.0625) * 9 / 5 + 32
	
# Reset Arduino to perform whatever reading

def resetArduino():
    GPIO.output(Reset, 1)
    time.sleep(.001)
    GPIO.output(Reset, 0)
    time.sleep(3)

def readArduino():
        temp = 0
        GPIO.output(CS, 1)
        # time.sleep(.002)
        for i in range(0,15): # loop here 15 times
                GPIO.output(CLK, 1)
                time.sleep(.001)
                temp = temp + GPIO.input(dataBit)
                GPIO.output(CLK, 0)
                temp = temp << 1 # shift 1 bit left
        GPIO.output(CLK, 1)
        time.sleep(.001)
        temp = temp + GPIO.input(dataBit) #  get bit 16
        GPIO.output(CLK, 0)
        GPIO.output(CS, 0)
        # clk one more time
        GPIO.output(CLK, 1)
        # time.sleep(.002)
        GPIO.output(CLK, 0)
        return temp

initLCD()

resetArduino()

gotoLocation(Line1)
writeString("Reading T:")

TReading = readArduino()
TempC = degC(TReading)
TempF = degF(TReading)


print TempC
print TempF

gotoLocation(Line1)
writeString("TC = ")

gotoLocation(Line1 + 5)
writeString(str(TempC))

gotoLocation(Line2)
writeString("TF = ")  

gotoLocation(Line2 + 5)
writeString(str(TempF))

GPIO.cleanup()

exit