Tag: Headless Pi

A little while ago someone showed me how their Raspberry Pi emailed them the DHCP assigned IP address, which is really useful for when running headless in a environment where you have no control over DHCP.  Now there are some alternatives, including running a Apple Zeroconf specification (like Bonjour), by installing “avahi-daemon”, but you need support on your client machine, which  needs a agent installing or other apple software (on Windows).

The main problem I had with the email method, is that unless you can find a open email relay (not a good idea), you need to include your email password (I’m sure with a little more time I find away of securing this, or using some kind of token).  So this set me thinking of what other presentation methods I could use to extract the IP address on boot.  Here are some of my ideas (If you search the web you’ll probably find these are not original) :

• Take control of the Power LED and flash it according to the IP address.
• Post the IP address to a website
• Plug in a Serial cable into the pi to get a console and just read the IP
• Connect a Display of some kind
• Read the IP address out of the audio jack

If you search the web you should find the info on controlling the Power LED, which I did consider this a good approach, but I finally settled on using the Audio out via some headphones.

Here is how I did it:-

1. Create a python script that reads the IP address:-
   • I made sure the audio player “aplay” is installed and working (Make sure the audio is set to come out the audio jack!)
   • Then I recorded a wav file for each number 0 – 9 and the decimal, ie 0.wav, 1.wav .. point.wav (had a little fun getting my Windows machine to record the right format; to to write raw wav)
   • Then  I wrote the following python to get and read the IP address (note I read the address used by the Ethernet port, as wireless would need you to connect to a access point first, but will work once the wireless config is established use ‘wlan0’ instead)

     import socket
     import fcntl
     import struct
     import os
     Import time
     
     def get_ip_address(ifname):
         s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
         return socket.inet_ntoa(fcntl.ioctl(
             s.fileno(),
             0x8915,  # SIOCGIFADDR
             struct.pack('256s', ifname[:15])
         )[20:24])
     
     #print get_ip_address('eth0')
     myip = get_ip_address('eth0')
     
     #myip = '10.10.100.32' # test
     
     
     for i in myip:
             time.sleep(1)
             if i == '1':
                     os.system('aplay /home/pi/readmyip/1.wav')
             elif i == '2':
                     os.system('aplay /home/pi/readmyip/2.wav')
             elif i == '3':
                     os.system('aplay /home/pi/readmyip/3.wav')
             elif i == '4':
                     os.system('aplay /home/pi/readmyip/4.wav')
             elif i == '5':
                     os.system('aplay /home/pi/readmyip/5.wav')
             elif i == '6':
                     os.system('aplay /home/pi/readmyip/6.wav')
             elif i == '7':
                     os.system('aplay /home/pi/readmyip/7.wav')
             elif i == '8':
                     os.system('aplay /home/pi/readmyip/8.wav')
             elif i == '9':
                     os.system('aplay /home/pi/readmyip/9.wav')
             elif i == '0':
                     os.system('aplay /home/pi/readmyip/0.wav')
             elif i == '.':
                     os.system('aplay /home/pi/readmyip/point.w$

2.  Call the Script at boot
   • Add the following to  “/etc/rc.local” file that which calls the  python script on boot.

     sudo python /<Python Script location>/<Python Script Name>.py

3.  Connect your headphones and restart your Pi.

You can refine this a little, especially if the Pi doesn’t get a IP address.