Nathan Stratton’s Homepage

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:

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!

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

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

Power

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

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

Closeup of status display and voltate meter

Software

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

I now can fill my pool without wasting water!

http://www.robotics.net/projects/home-automation/pool-fill

-Nathan