Tuesday, December 4, 2012

Dual power supplies is the way to go

You may notice in the picture of my setup (in the previous post) that the Raspberry Pi is being powered normally via the USB power connector.  This was done because the Pi was failing to boot when powered through the GPIO port as I had planned.  While I did not do any tests, the obvious cause is a lack of sufficient current to power the Pi.  It really does want to have a solid 700mA of 5 volt juice.  My planned configuration worked fine on the workbench but failed once I mounted it on the wall and connected the alarm sensors.  The sensors require 12V power and I was using the same power supply to drive the sensors and the power adapter for the interface board.  That 12V power supply was only 2A and that was apparently too little for all of this.

I could have gotten a larger 12V power supply, but I already have several of these 2A supplies. Realization finally struck me that using a single power supply would be a mistake.  If any of the sensor lines was compromised, shorting the power to ground, it would cause the Pi to shut down suddenly.  So now I have one supply just for the alarm sensors and another that drives the interface board, and through that, the Pi.

The system is up and has been running for over a week with no major problems.  I spent several hours improving my code for driving the X10 interface to make it as reliable as possible.  It seems to work as well as it ever has when using heyu or ActiveHome to drive it.  X10 is inherently unreliable, but is usually good enough for casual use.  If you have a fairly new house that is wired properly, then it can work fairly well.  My house, unfortunately, is old and poorly wired.  I have made some improvements over the years, but there are still areas of my house that the X10 signals simply will not reach.  I will cover X10 in more detail in an future post.


  1. Dear Ted,

    I hated to go this route to contact you, but I can't find a "contact" link anywhere. (Maybe that's intentional . . . ?)

    I found you in the RasPi boards talking about your security system install. I'm looking for advice / experience with a project that would literally be considered life or death (no hyperbole here!). I wondered if I could pick your brain.

    My email is joekoday@gmail.com. If you could spare a little time?

    Thank you,


  2. Hi Ted,

    I am Kavita.

    We have recently published a new book titled "Raspberry Pi Home Automation with Arduino ( http://www.packtpub.com/raspberry-pi-home-automation-with-arduino/book ) " and are currently looking out for experts who could review this book on their blog/website and Amazon.

    Looking at your expertise in Raspberry Pi, I was wondering in case you'd be interested, please let me know on.

    Kavita Pandey