This entry contributes a simple Bash script to query and control a LM75 Digital Temperature Sensor via I2C. The second Bash script is a utility to interact with a real-time clock (RTC). The third entry is a Python script for a mini web server to retrieve the temperature in either Celsius (default) or Fahrenheit. These were a few very fun weekend…

lm75a.sh

#!/bin/bash

readonly lm75=0x48 # Slave address with A0, A1, and A2 set to 0v (ground).

while [ $# -gt 0 ]
do
   if [ "$1" == "-debug" ]
   then
      debug=true
   fi

   if [ "$1" == "-on" ]
   then
      i2cset -y -m 0x01 1 $lm75 0x01 0x00 b
   fi

   if [ "$1" == "-off" ]
   then
      i2cset -y -m 0x01 1 $lm75 0x01 0x01 b
   fi

   if [ "$1" == "-f" ]
   then
      fahrenheit=true
   fi

   if [ "$1" == "-reset" ]
   then
      i2cset -y 1 $lm75 0x01 0x00 b
      i2cset -y 1 $lm75 0x02 0x004B w
      i2cset -y 1 $lm75 0x03 0x0050 w
   fi

   if [ "$1" == "-set" ] # Bash shell does not support floating point types - please avoid floating point input.
   then
      shift

      tos=$1

      shift

      thy=$1

     if [ $tos -gt $thy ]
     then
        tos=$(($tos & 0xffff))
        tos=$(echo "$tos / 0.125" | bc)
        t=$(($tos << 5))
        t=$(($t & 0xffff))
        t=$(($(($t << 8)) | $(($t >> 8))))
        t=$(($t & 0xffff))

        i2cset -y 1 $lm75 0x03 $t w

        thy=$(($thy & 0xffff))
        thy=$(echo "$thy / 0.125" | bc)
        t=$(($thy << 5))
        t=$(($t & 0xffff))
        t=$(($(($t << 8)) | $(($t >> 8))))
        t=$(($t & 0xffff))

        i2cset -y 1 $lm75 0x02 $t w
     else
        echo "Tos register should be greater than Thyst register. Aborted."
        exit
     fi
   fi

   shift
done

tmp_raw=$(i2cget -y 1 $lm75 0x00 w)

if [ "$debug" = true ]
then
   # Setup for debugging - convert into binary.
   D2B=({0..1}{0..1}{0..1}{0..1}{0..1}{0..1}{0..1}{0..1})

   cnf_raw=$(i2cget -y 1 $lm75 0x01 b)
   thy_raw=$(i2cget -y 1 $lm75 0x02 w)
   tos_raw=$(i2cget -y 1 $lm75 0x03 w)

   dbg_tmp_lo_byte=${tmp_raw:2:2}
   dbg_tmp_hi_byte=${tmp_raw:4:2}

   dbg_thy_lo_byte=${thy_raw:2:2}
   dbg_thy_hi_byte=${thy_raw:4:2}

   dbg_cnf_lo_byte=${cnf_raw:2:2}

   dbg_tos_lo_byte=${tos_raw:2:2}
   dbg_tos_hi_byte=${tos_raw:4:2}

   echo "Raw Temp register:  0x$dbg_tmp_hi_byte 0x$dbg_tmp_lo_byte [${D2B[0x$dbg_tmp_hi_byte]} ${D2B[0x$dbg_tmp_lo_byte]}]"
   echo "Raw Conf register:  ---- 0x$dbg_cnf_lo_byte [-------- ${D2B[0x$dbg_cnf_lo_byte]}]"
   echo "Raw Thyst register: 0x$dbg_thy_hi_byte 0x$dbg_thy_lo_byte [${D2B[0x$dbg_thy_hi_byte]} ${D2B[0x$dbg_thy_lo_byte]}]"
   echo "Raw Tos register:   0x$dbg_tos_hi_byte 0x$dbg_tos_lo_byte [${D2B[0x$dbg_tos_hi_byte]} ${D2B[0x$dbg_tos_lo_byte]}]"
fi

adj_neg=0
adj_tmp=$(($(($tmp_raw >> 8)) | $(($tmp_raw << 8))))
adj_tmp=$(($adj_tmp & 0xffff))

# Check if the MSB (of the word) is set to indicate a negitive value
if [[ $(($adj_tmp & 0x8000)) -eq 0x8000 ]]
then
   adj_neg=256
fi

adj_tmp=$(($adj_tmp >> 5))

if [ "$fahrenheit" = true ]
then
   echo "scale=3; (($adj_tmp * 0.125) - $adj_neg) * (9 / 5) + 32" | bc
else
   echo "scale=3; ($adj_tmp * 0.125) - $adj_neg" | bc
fi

pcf2127.sh

#!/bin/bash

readonly rtc=0x51 # Slave address.

readonly alm_flg=0x10

while [ $# -gt 0 ]
do
   if [ "$1" == "-debug" ]
   then
      debug=true
   fi

   if [ "$1" == "-unload" ]
   then
      modprobe -r rtc_pcf2127 # Must have admin access.
   fi

   if [ "$1" == "-load" ]
   then
      modprobe rtc_pcf2127 # Must have admin access.
   fi

   if [ "$1" == "-12" ] # Set 12 hour clock.
   then
      i2cset -y -m 0x04 1 $rtc 0x00 0x04 b
   fi

   if [ "$1" == "-24" ] # Set 24 hour clock.
   then
      i2cset -y -m 0x04 1 $rtc 0x00 0x00 b
   fi

   if [ "$1" == "-clear" ] # Clear the alarm flag.
   then
      i2cset -y -m 0x10 1 $rtc 0x01 0x00 b
   fi

   if [ "$1" == "-reset" ] # Disable and zero the alarm.
   then
      i2cset -y -m 0xFF 1 $rtc 0x0A 0x80 b
      i2cset -y -m 0xFF 1 $rtc 0x0B 0x80 b
      i2cset -y -m 0xFF 1 $rtc 0x0C 0x80 b
      i2cset -y -m 0xFF 1 $rtc 0x0D 0x80 b
      i2cset -y -m 0xFF 1 $rtc 0x0E 0x80 b
   fi

   if [ "$1" == "-set" ] # Set the alarm - hours, minutes, and seconds.
   then
      shift

      hrs=$1

      shift

      min=$1

      shift

      sec=$1

      i2cset -y -m 0xFF 1 $rtc 0x0A 0x$sec b
      i2cset -y -m 0xFF 1 $rtc 0x0B 0x$min b
      i2cset -y -m 0xFF 1 $rtc 0x0C 0x$hrs b
   fi

   shift
done

rtc1_raw=$(i2cget -y 1 $rtc 0x01 b)

if [ "$debug" = true ]
then
   # Setup for debugging - convert into binary.
   D2B=({0..1}{0..1}{0..1}{0..1}{0..1}{0..1}{0..1}{0..1})

   rtc0_raw=$(i2cget -y 1 $rtc 0x00 b)
 # rtc1_raw=$(i2cget -y 1 $rtc 0x01 b)
   rtc2_raw=$(i2cget -y 1 $rtc 0x02 b)

   alm_sec_raw=$(i2cget -y 1 $rtc 0x0A b)
   alm_min_raw=$(i2cget -y 1 $rtc 0x0B b)
   alm_hrs_raw=$(i2cget -y 1 $rtc 0x0C b)
   alm_day_raw=$(i2cget -y 1 $rtc 0x0D b)
   alm_wkd_raw=$(i2cget -y 1 $rtc 0x0E b)

   echo "RTC control 1 register: $rtc0_raw [${D2B[$rtc0_raw]}]"
   echo "RTC control 2 register: $rtc1_raw [${D2B[$rtc1_raw]}]"
   echo "RTC control 3 register: $rtc2_raw [${D2B[$rtc2_raw]}]"

   echo "ALM seconds register:   $alm_sec_raw [${D2B[$alm_sec_raw]}]"
   echo "ALM minutes register:   $alm_min_raw [${D2B[$alm_min_raw]}]"
   echo "ALM hours register:     $alm_hrs_raw [${D2B[$alm_hrs_raw]}]"
   echo "ALM days register:      $alm_day_raw [${D2B[$alm_day_raw]}]"
   echo "ALM week day register:  $alm_wkd_raw [${D2B[$alm_wkd_raw]}]"
fi

sec_raw=$(i2cget -y 1 $rtc 0x03 b)
min_raw=$(i2cget -y 1 $rtc 0x04 b)
hrs_raw=$(i2cget -y 1 $rtc 0x05 b)
day_raw=$(i2cget -y 1 $rtc 0x06 b)
mth_raw=$(i2cget -y 1 $rtc 0x08 b)
yar_raw=$(i2cget -y 1 $rtc 0x09 b)

sec1_raw=$((${sec_raw:2:1} & 0x7))
sec2_raw=${sec_raw:3:1}

echo "Date (UTC): 20${yar_raw:2:2}-${mth_raw:2:2}-${day_raw:2:2} ${hrs_raw:2:2}:${min_raw:2:2}:${sec1_raw}${sec2_raw}H"

if [[ $(($rtc1_raw & $alm_flg)) -eq $alm_flg ]]
then
   echo "Alarm"
fi

web.py

#!/usr/bin/env python

import socket
import os

host = ""
port = 8080
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock.bind((host, port))
sock.listen(1)

while True:
    try:
        csock, caddr = sock.accept()
        print "Connection from: " + `caddr`
        request = csock.recv(1024) # Get the request, 1kB max.
        request = request.splitlines()[0]
        print request
        if request.startswith("GET"):
            if request.find("style=f") == -1:
                if request.find("debug=true") == -1:
                    p = os.popen("./lm75a.sh")
                else:
                    p = os.popen("./lm75a.sh -debug")
            else:
                p = os.popen("./lm75a.sh -f")
            t = p.read()
            csock.sendall("HTTP/1.1 200 OK" + "\r\n" + "Content-Type: text/plain" + "\r\n" + "Cache-Control: no-cache, no-store, must-revalidate"  + "\r\n" +  "Expires$
        else:
            csock.sendall("HTTP/1.1 404 Not Found\r\nContent-Length: 0\r\n\r\n")
        csock.close()
    except:
        pass