Nathan Stratton’s Homepage

Tag: Hack

Hello World, the current temp is:

by on May.02, 2010, under Hardware, Software

I have wanted to start playing with micro controllers for a while now, I ended up selecting the Parallax Propeller chip because of its ease of use and I liked it’s COG design with 8 32 big cores working together.

My first test was connecting a 4×20 line LCD and a few DS18S20 1-wire temp sensors to the propeller chip. Everything was very easy to learn the LCD was interfaced with no external components and the 1-wire bus only required a 4.7K pull up resistor.

Propeller PDB with LCD and 1-wire bus

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Central Air Pool Heat-Cool

by on Apr.24, 2010, under Projects

Worked today on my central air pool heat/cool system. The goal for the new system is to be able to operate in normal house cool mode, pool heat mode, and pool cool mode all in one HVAC system. The new system uses a reversing valve to pump down unused portions dramatically cutting down on the amount of refrigerant needed.


Check out the project page for more info:

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APC Matrix 5000 Hack

by on Jul.19, 2009, under Hardware

I use a lot of power in my office, so much that the four 1500 VA UPS units I have only last me a few min. I needed something bigger so I went on eBay and found two APC Matrix 5000 UPS units for $450 each including shipping. There was only one downside, there were no batteries and new batteries would have cost me several thousand dollars.

The solution? I picked up 8 marine batteries at the auto parts store and wired them up (yes with fuses) into two 48 volt strings connected in parallel.


Note: If you try this, you want to use Marine or better yet Deep-Cycle batteries rather then car starting batteries. Car batteries are designed to give very hight bursts of current and should only be discharged to about 5%. The very thin plates would destroyed over a few hundred discharges rather then the thousands you would get from deep cycle.

P.S. Yes, I built a cover for it!

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Converting Citrix .xva to .img

by on Jun.06, 2009, under Software

Xen is one of the coolest virtualization technologies out there. It comes in may flavors, the two largest being the bleeding edge open source project and the commercial (Citrix) version. There are things I love about the commercial version, but they lost me only supporting windows in their XenCenter administration interface.

The file formats of the commercial and open source Xenare totall different. The open source is a standard image file, you can mount it, fdisk it, whatever you would like. The Citrix Xen Virtual Appliance .XVA file is quite different. It is actually a tar file with ova.xml meta data and directories starting with Ref full of 1M files that make up the drive volumes of the virtual image.

To convert .xva to an xen .img file you first untar the image:

tar -xvf {image}.xva

Then grab this handy utility and run it on your untared data, as an example:

python –convert=Ref:3 {image}.img

This will paste all of those files back together, starting at 00000000. Note I have had problems running this script on Centos 5.x.

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Portable 3 Watt 3G Video Phone and HotSpot

by on Jun.02, 2009, under Hardware

I love my BlinkMind Video Phone service, but one problem has been being able to make calls when I am camping. I started by looking for a 3G access point that was already supported by OpenWRT, a Linux distribution for embedded devices. Since I run the Linksys WRT54G at home, the WRT54G3G was a logical choice.

Get Linux Running

Getting Linux Running on the WRT54G3G can be a pain since it’s PCMCI implementation does not work on the 2.6 kernel series. To make matters worse, Sierra Wireless only wrote and supports drivers for the 2.6 kernel. You can grab a copy of OpenWRT White Russian here for the BCM47xx chip set, next grab a hex editor (I used shed on Fedora) and change the 4 bytes to W3GA, once that is done you should be able to fire up the unit and upgrade the firmware with the edited image. If your lazy you can just download this.

Add a LCD

I selected a 4 line X 20 Character LCD display that could be used to show the IP address, upload / download speed, and signal strength. Modern Device made a nice little serial to LCD board that makes it VERY easy to connect a LCD to any service device.


Modern Device LCD117 Board

RT204-1 20x4 LCD

RT204-1 20x4 LCD

Download PDF Instructions

The WRT45G3G does not have an external serial port, but internally it does have pads for a 3.3V serial. If you wanted to drive a computer serial port you would need a level converter such as MAX232. However, the Modern Device board is able to accept 3.3V without a problem. The only catch was finding the right pin. I broke out a logic probe and send some data out the port in pulses to eventually find the pin.

Receive and Transmist pads

Receive and Transmist pads


I wanted the system to be able to run off batter for at least a few hours so I decided to go with two 6V 6.5AH batteries in series rather then a single 12 volt battery. The size allowed them to lay down on the bottom of my case. The LCD runs off 5 Volts, the easiest way to make this work with parts on hand was to use a +5 Volt regulator that fit nicely on one of the 4 mounting screwed for the router. Current draw is low enough that no heat sink is needed. I also added a 12 volt LCD voltage meter to the mix so I could tell when my batteries were running low.

Two 6 Volt 6.5 AH Batteries

Two 6 Volt 6.5 AH Batteries

3G Wireless

3G is via Sierra Wireless 881 PCMCI 3G card with AT&T service. I quickly realized that the default signal strength was not going to cut it and an amplifier would be needed. After some digging I selected Wilson Electronics 801101 3 watt cellular amp with in conjunction with a ARC Wireless Solutions ARC-FR0803R30 antenna. With the antenna I was able to buy a cable to connect to the Sierra card, but it required a 6 foot FME Female – FME Female cable that I replaced with a 1 inch FME Female coupler.

Putting Parts Together


Portable 3 Watt 3G Video Phone and HotSpot

Back of router board

Back of router board

Closeup of status display and voltate meter

Closeup of status display and voltate meter


I wanted the display to show some useful, current script runs at startup and displays IP address, upload and download avg bandwdith in kb/s, and Signal strength in dBm.

Download Script


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Mounting a 2.5″ hard drive in slim floppy bay

by on May.08, 2009, under Hardware

I have been looking for a way to move to removable 2.5″ boot/root disks on our servers. I am using all of the 3.5″ removable trays for storage leaving only a slim floppy bay in the case.

Supermicro 836S2-R800V

Supermicro 836S2-R800V

After much searching I found Thermaltake ST0002Z, a dual 2.5″ hot swap enclosure that mounts in a standard 3.5 inch floppy bay.

Thermaltake ST0002Z

Thermaltake ST0002Z

The two hot swap bays are actually 2 units that are bolted together making it very easy to take this apart and get yourself a nice 2.5 inch SATA bay that will fit in a slim floppy bay.

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