Wake-on-lan remote interface

This software provides a way to wake (via wake-on-lan) machines on a remote network.

After making my home PC accessible externally via Dynamic DNS, I needed a way to remotely power it on and off, since leaving it on 24/7 would run up a large energy bill.  I took one of my (many) Raspberry Pi computers and set up a script to log the MAC addresses of all machines detected on the network, along with corresponding IP addresses and hostnames.  This script runs periodically as a cron job, providing a list of machines by name or last known IP, and their associated MAC addresses.

A web interface allows any PC from this database to be chosen, and for a wake-on-lan magic packet to be dispatched to it.  Provided the PC is connected to the network via an ethernet cable and wake-on-lan is enabled on the associated adapter, the end result is that the chosen PC will turn on in response to me clicking a button in my web browser from 40 miles away.

The PC must be wired into the network in order to receive wake-on-lan packets, but there can be wireless links between the router/switch that the PC is wired to and the Raspberry Pi.  Wake-on-LAN magic packets are sent as UDP broadcasts in my script, although they could be in any type of container that will get routed to the target PC’s ethernet port.

Download: Remote Wake-on-LAN, MAC database scripts and web interface
Latest version (github): battlesnake/macs

Dynamic DNS server

This software provides a cheap dynamic DNS solution for anyone with a Linux VPS (or a friend who is willing to share one).

I occasionally want to access my home PC while I’m away from home, but my ISP doesn’t offer static IP addressing.  Thanks to a resurgence in the popularity of virtualisation, servers are extremely cheap to rent nowadays (as little as £3/month).  In addition to the server hosting this website (and others), I run a DNS nameserver (using PowerDNS) on one of my other virtual servers.  With this simple BASH script and a web interface, my server gained dynamic DNS capabilities and allows me to access my home PC despite the varying IP address.

The packaged script and web interface run on the nameserver, and a separate script is run on the target machine (in my case, the home PC), which curl’s the web interface periodically to update the necessary A-record.  It is important for the A-record to have a small TTL value (e.g. 60 seconds), in order to allow updates to propagate through DNS caches at a reasonable speed.  Look at the code for the PHP web interface to understand the syntax for the CURL request.

Rather than leave the home PC on 24/7 and waste electricity, I also created a remote interface to dispatch wake-on-lan packets.

Download: Dynamic DNS scripts
Latest version (github): battlesnake/ddns

Dielectric: Electrical and acoustic spectroscopy via a PC sound card

This program generates a chirp signal, sweeping over a given frequency range, and drives a given audio output with the signal, while simultaneously analysing the signal coming from an audio input.  This allows electrical spectroscopy and acoustic spectroscopy from ~10Hz-100 kHz to be performed with a £40 sound card.  Note that AC97-channels (such as on-board sound) have lowpass filters built in, restricting the upper limit to around 25 kHz.  Tested with a Creative Audigy 2 ZS, using kX v5.1 drivers.

Download here.

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