DIY project with the versatile Arduino board

Like Magic

Article from Issue 159/2014
Author(s):

With a few lines of self-written firmware and a simple Perl script, Perlmeister Mike Schilli trains one of his Linux computers with a plugged in Arduino board to switch electrical equipment on and off using a relay. Enchanting.

Every morning at four o'clock, the Ubuntu system in my office switches on an ancient Debian PC with 6TB of disk space to grab a backup of important data via rsync. It uses the popular home networking protocol X10 to switch on the power on the backup PC via the power grid. The backup PC boots automatically, because its Boot After Power Loss BIOS option is set to On. Once the SSH server on the running Debian system responds, the backup starts. After the final act, the PC shuts down, and the controlling Ubuntu box cuts the power.

Because my X10 setup fails for some reason in an estimated 1 out of 100 cases, I have now converted the PC on/off control to an Arduino board (around US$ 20) with an attached Relay Board (US$ 12). The controlling Ubuntu machine uses the USB port to send a command to the microcontroller, which listens on a serial interface.

The microcontroller's firmware switches the signal on an output pin, which I have connected to one of two relays on an extra board [1]. Figure 1 shows the set up with a simple circuit on a breadboard. For test purposes, it even uses light-emitting diodes to indicate whether a specific output pin on the Arduino is on or off.

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