WARNING: The following guide involves serious plumbing and electrical work. The electrical box on most pool involves 240volt ac electricity. This is DANGEROUS and can kill you INSTANTLY. You should not attempt work inside your electrical box unless you absolutely know what you are doing, otherwise consult a licensed electrician. Don't gamble with your life to save a buck.

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Before we begin here, it should be understood that the reader of this guide is expected to be very knowledgeable with linux, electronics, and have a good ability to read guides for how to wire electrical and plumbing. This guide is intended to be more of a guide as to what components will work together, what's a good cheap way to get it done and an introduction to what is possible.

This is an instructional guide on how to replicate my (unbelievably successful) efforts to build an open source open hardware pool control system using cheap used parts from eBay. The total cost of the system is just north of $300 and the functionality is impressive. The reason this all came about is that I have a 25 year old in-ground pool in the home I recently bought. All of the equipment and controls are quite old and they are quite similar to the controls many people have for a pool. They consist of a light switch inside an outdoor electrical box to turn on an underwater light, some circuit breakers and a mechanical rotary timer. The timer has basically an infinite number of positions but in my case the timer came with no triggers! I searched high and low and couldn't find replacement triggers. This meant I would need to change to a new intermatic timer mechanism at a cost of over $60. What's the point of that when I can spend a couple hundred more on something truly cool. Another thing that truly irked me is that at *night* when I wanted the *light* I had to fiddle my way in a 240 volt box to find the light switch possibly frying myself with wet hands. It just didn't seem logical. I wanted the switch to be on a remote control or at very least on the wall in the house. When I go on vacation or am at work I want to be able to check in and KNOW that my equipment is functioning properly.

Phase I Ingredients:
TOOLS! Spade bits for drill, screw drivers, soldering irons, etc. You should be a DIY dork to begin with.

Linksys NSLU2 - Small ARM based Linux computer ($56.98 shipped eBay)
Linksys WUSB54G - USB 802.11g adapter (free, laying around)
Targus 4 port micro USB hub ($20, but free laying around)
Arduino Decimilla ($33.50 adafruit)
Arduino protoshield ($12.50 adafruit)
Kingston 4GB USB Flash Drive (free, laying around but as cheap as $30)
4x8x8 waterproof NEMA 6P Junction Box (8x8x4 version of this)($35.00 Lowes)
Liquidtight conduit kit ($12.95 Lowes)
3 TIP102 Power Transistors (3, $1.86 Mouser)
3 Fujitsu Relays (3, $6.45 Mouser)
3 definite purpose 2 pole 240volt contactors (24vac trigger) I bought something like the linked contactor on ebay for $9 each
1 MCP120-450DI/TO Power supply monitor (1, $0.41 Mouser)
24 volts AC transformer eBay $14.98 shipped
Small things from Lowes: Electrical Outlet kit (to make a new outlet from a cord), black and white lengths of 8 gauge solid core copper wire (though I think now stranded might have been easier to work with), "Bell Wire" - found near doorbells in a nice long prepackaged spool, velcro stickers.

Phase II Ingredients:
Nokia 770 $82.95 shipped, eBay
Required plumbing components to retrofit 3 3/4" tees into your system ($40-$50 for me, could be next to nothing for you)
2 LM34 temperature sensors (2, $7.90 Mouser)
1 length of stainless steel brake line (bring the LM34 to make sure it fits) (Advance Auto, cheap)
2 Freescale MPX5500 pressure sensors (2 for $22.58, Mouser)
CAT5 cable (preferably an outdoor rated cable) which works well for hooking up the sensors (free, laying around)
More liquidtight conduit and fitting (Lowes)

Step 1: Evaluate your desired complexity
This system is fully customizable. You can control as little or as much as you want! You could do something as simple as a 1 contactor control of your pump to run the pump based on the daylight hours or some other control. You could get away with running that with just the arduino and no computer whatsoever! This would be a dirt cheap timer, cheaper than the mechanical replacement timer probably. You can go as complex as a system that can tell the temperature of a solar array and divert flow to it, protect your pump from burnout, allow internet based controls, touch screen turn lights on and off, etc. Keep this in mind. I will describe the system as it applies to my installaton but the sky is really the limit here.

Phase I: Electrical Control
Phase II: Sensors and Data Aquisition
Phase III: Touch screen controls and polish