Raspberry Pi iButton System- Updated

Reading ibuttons using a Raspberry Pi can be a lot easier than you think. We published a post about a Raspberry Pi iButton System a while ago and we were overwhelmed how popular the post was. So we decided to write an updated tutorial on the Raspberry Pi iButton System. This post describes the most basic method of reading an ibutton and the obtained ibutton identification number / Serial number is displayed on an LCD screen. To get started, please refer to our original post.

Data from the DS1990 ibutton is transferred serially through the 1-Wire protocol, which requires only a single data lead and a ground return. The 1-wire interface on a raspberry pi can be access by using the w1-gpio kernel on Linux running on the raspberry pi.

Activate the 1-wire Bus Driver and the GPIO

First of all, install the latest version of Raspbian on an SD card and then power and boot your Pi. In the latest Linux kernel, the 1-wire feature is disabled by default. To enable it, add the following line to /boot/config.txt and reboot the Pi.

dtoverlay=w1-gpio,gpiopin=4

Use the following command to active the 1-wire bus driver and the GPIO:

sudo modprobe w1-gpio
sudo modprobe w1-smem

And set the permissions for the 1-wire bus folder:

sudo chmod a+w /sys/devices/w1_bus_master1/w1_master_slaves
sudo chmod a+w /sys/devices/w1_bus_master1/w1_master_remove
sudo chmod a+w /sys/devices/w1_bus_master1/w1_master_search

RASPBERRY PI IBUTTON connections

For this post, we decided to connect an LCD to display the ID of the ibutton. For detailed connections for the LCD, please visit our previous post.

The center of the ibutton probe is connected to the GPIO-4 of the Pi, with a 1k pull-up resistor between the GPIO-4 and the 3.3V pin and the outer contact is connected to the Pi’s ground.

Python script

The following python script allows the Ibutton to be read and the results is displayed on the LCD for 3 seconds. Most of the code is to drive the LCD and the core ibutton reading code is labelled “# iButton Read”

#!/usr/bin/python
#--------------------------------------
#  Rasbperry Pi ibutton with LCD Test Script
#
# Author : BehindTheSciences
# Date   : 15/02/2017
#
# https://behindthesciences.com
#
#--------------------------------------
import os
import time
import RPi.GPIO as GPIO
# Commands
LCD_CLEARDISPLAY        = 0x01
LCD_ENTRYMODESET        = 0x04
LCD_DISPLAYCONTROL      = 0x08
LCD_FUNCTIONSET         = 0x20
LCD_SETDDRAMADDR        = 0x80
# Entry flags
LCD_ENTRYLEFT           = 0x02
LCD_ENTRYSHIFTDECREMENT = 0x00
# Control flags
LCD_DISPLAYON           = 0x04
LCD_CURSOROFF           = 0x00
LCD_BLINKOFF            = 0x00
# Function set flags
LCD_4BITMODE            = 0x00
LCD_2LINE               = 0x08
LCD_1LINE               = 0x00
LCD_5x8DOTS             = 0x00
# Offset for up to 4 rows.
LCD_ROW_OFFSETS         = (0x00, 0x40, 0x14, 0x54)

# GPIO to LCD mapping
LCD_RS            = 14
LCD_EN            = 18
LCD_D4            = 24
LCD_D5            = 23
LCD_D6            = 8
LCD_D7            = 25
# Define some device constants
LCD_WIDTH = 16    # Maximum characters per line
LCD_CHR = True
LCD_CMD = False
LCD_LINE_1 = LCD_SETDDRAMADDR # LCD RAM address for the 1st line
LCD_LINE_2 = LCD_SETDDRAMADDR | LCD_ROW_OFFSETS[1] # LCD RAM address for the 2nd line
 
# Timing constants
E_PULSE = 0.0005
E_DELAY = 0.0005
print(time.strftime("%c"))
 
os.system('modprobe wire timeout=1 slave_ttl=5')
os.system('modprobe w1-gpio')
os.system('modprobe w1-smem')
os.system('chmod a+w /sys/devices/w1_bus_master1/w1_master_slaves')
os.system('chmod a+w /sys/devices/w1_bus_master1/w1_master_remove')
os.system('chmod a+w /sys/devices/w1_bus_master1/w1_master_search')
base_dir = '/sys/devices/w1_bus_master1/w1_master_slaves'
delete_dir = '/sys/devices/w1_bus_master1/w1_master_remove'
  
def main():
  # Main program block
  GPIO.setwarnings(False)
  GPIO.setmode(GPIO.BCM)       # Use BCM GPIO numbers
  GPIO.setup(LCD_EN, GPIO.OUT)  # EN
  GPIO.setup(LCD_RS, GPIO.OUT) # RS
  GPIO.setup(LCD_D4, GPIO.OUT) # DB4
  GPIO.setup(LCD_D5, GPIO.OUT) # DB5
  GPIO.setup(LCD_D6, GPIO.OUT) # DB6
  GPIO.setup(LCD_D7, GPIO.OUT) # DB7
 
  # Initialise display
  lcd_init()
 
  while True:
 
    # iButton Read
	f = open(base_dir, "r")
	ID = f.read()
	f.close()
	if ID != 'not found.\n':
		print(ID)
		lcd_string("iButton ID = ",LCD_LINE_1)
		lcd_string(ID,LCD_LINE_2)
		time.sleep(3)
		d = open(delete_dir, "w")
		d.write(ID)
	else:
		lcd_string("Waiting...",LCD_LINE_1)
		lcd_string(time.strftime("%c"),LCD_LINE_2)
     
def lcd_init():
  # Initialise display
  lcd_byte(0x33,LCD_CMD) # 110011 Initialise
  lcd_byte(0x32,LCD_CMD) # 110010 Initialise
  # 000110 Cursor move direction
  lcd_byte(LCD_ENTRYMODESET | LCD_ENTRYLEFT | LCD_ENTRYSHIFTDECREMENT,LCD_CMD) 
  # Initialize display control, function, and mode registers.
  # 001100 Display On,Cursor Off, Blink Off
  lcd_byte(LCD_DISPLAYCONTROL | LCD_DISPLAYON | LCD_CURSOROFF | LCD_BLINKOFF,LCD_CMD)
  # 101000 Data length, number of lines, font size
  lcd_byte(LCD_FUNCTIONSET | LCD_4BITMODE | LCD_1LINE | LCD_2LINE | LCD_5x8DOTS,LCD_CMD) # 101000 Data length, number of lines, font size
  # 000001 Clear display
  lcd_byte(LCD_CLEARDISPLAY,LCD_CMD) 
  time.sleep(E_DELAY)
 
def lcd_byte(bits, mode):
  # Send byte to data pins
  # bits = data
  # mode = True  for character
  #        False for command
 
  GPIO.output(LCD_RS, mode) # RS
 
  # High bits
  GPIO.output(LCD_D4, False)
  GPIO.output(LCD_D5, False)
  GPIO.output(LCD_D6, False)
  GPIO.output(LCD_D7, False)
  if bits&0x10==0x10:
    GPIO.output(LCD_D4, True)
  if bits&0x20==0x20:
    GPIO.output(LCD_D5, True)
  if bits&0x40==0x40:
    GPIO.output(LCD_D6, True)
  if bits&0x80==0x80:
    GPIO.output(LCD_D7, True)
 
  # Toggle 'Enable' pin
  lcd_toggle_enable()
 
  # Low bits
  GPIO.output(LCD_D4, False)
  GPIO.output(LCD_D5, False)
  GPIO.output(LCD_D6, False)
  GPIO.output(LCD_D7, False)
  if bits&0x01==0x01:
    GPIO.output(LCD_D4, True)
  if bits&0x02==0x02:
    GPIO.output(LCD_D5, True)
  if bits&0x04==0x04:
    GPIO.output(LCD_D6, True)
  if bits&0x08==0x08:
    GPIO.output(LCD_D7, True)
 
  # Toggle 'Enable' pin
  lcd_toggle_enable()
 
def lcd_toggle_enable():
  # Toggle enable
  time.sleep(E_DELAY)
  GPIO.output(LCD_EN, True)
  time.sleep(E_PULSE)
  GPIO.output(LCD_EN, False)
  time.sleep(E_DELAY)
 
def lcd_string(message,line):
  # Send string to display
 
  message = message.ljust(LCD_WIDTH," ")
 
  lcd_byte(line, LCD_CMD)
 
  for i in range(LCD_WIDTH):
    lcd_byte(ord(message[i]),LCD_CHR)
 
if __name__ == '__main__':
 
  try:
    main()
  except KeyboardInterrupt:
    pass
  finally:
    GPIO.cleanup()

The python script can also be downloaded here.
By default, the 1-wire kernel only reads the GPIO-4 every 10 seconds. To speed the reading time;
Edit this file as Sudo

/etc/modprobe.d/w1.conf

Add this text:

options wire timeout=1 slave_ttl=3

Here is a few photos; we did not have a spare ibutton probe for this post, hence used 2 wires to make the contact.