Hey all.

I've been toying with some ideas for my AWC, and thought it'd be easier to first incorporate them into a workable ATO. This is a standard relay based ATO, with provision for redundant floatswitches - nothing exotic. I've seen some great DIY jobs of this type, but thought it would also be of value to the community to put together a low-cost and easy-to-use PCB and 'kit' for people to use. I've also added the first feature - the design includes a simple onboard AC adapter - all you have to provide is normal house power.

The 'kit' is basically a digikey parts list for completing the board. It does not include the external floatswitches, pump, or housing, as those are something that are more specific to your setup. I may search out a good general-purpose housing and scale the PCB to fit in a later revision.

On to the good stuff:



You'll need one of each of the following:
PCB
Transformer
Rectifier
Capacitor
Relay
Diode
Terminal Strip

Total cost - $19.67


If you've got an idea for improvement, I'm all ears - let me know what you want in an ATO. Housing? External Connectors? Debounce? Timer? High-level alarm?

I've made some upgrades to the design. It now includes overcurrent protection, a voltage regulator, as well as a simple RC timer. This adds an additional layer of redundancy. The relay will shut off after an adjustable time delay, or if the backup floatswitch is lifted. It also removes the absolute requirement to have a backup floatswitch, should you so desire - simply short the backup floatswitch terminals with a jumper. I would not personally run it this way, but this may be of benefit in very small tanks where a second float will not fit.

On to the good stuff:

Here's the printed circuit board itself. Don't worry about understanding it if you don't want to; all you need to do is solder the components to the board.



You'll need the following:

PCB - $17.46
Rectifier - $0.51
3300uF Capacitor - $0.82
Transformer - $3.15
Relay - $2.58
Diode - $0.27
Fuse Holder X2 - $0.61 ea
1A Fuse - $0.32
1M Potentiometer - $0.83
0.1uF Capacitor - $0.18
10uF Capacitor - $0.16
Terminal Strip - $1.26
MOSFET - $0.68
12V Regulator - $0.54
100mA Fuse - $1.34
10k Resistor - $0.15

Total Cost - $31.32. The truly frugal could cut the cost in half by duplicating the circuit on a perforated board, if they felt up to the task.

For the floatswitches, you may use whatever you like, so long as it is "normally closed". This means that when the water level drops, the switch turns "on". I personally use the FLT015 from Chicago sensor - this is the floatswitch from the now defunct www.floatswitches.net, which used to be the goto place for DIY ATO's. It was sad to see them go, but at least the switches are still available to us. The cost on the switches is $7.00 each. For the price, I'd pick up an extra to keep on hand in case you have a failure.


For my fellow Canadians - you will need to use a different relay, as the relay above is not in stock on digikey.ca

Canadian Relay - $2.39.

You'll also find that the prices on all of the other components are slightly higher, though that's not a surprise, is it?

Digikey has some weird script for determining which site to show you - the links to the parts are the same, but you must first go to www.digikey.ca and leave the tab open before clicking the links.

I have also put together a barebones kit. This is a lower cost ATO that does not include the features of the V1.3. It requires an external 12V power supply, and does not include the RC timer. It does, however, still have a connection for a backup floatswitch.




Parts List:

PCB - $10
Relay - $2.58
Diode - $0.27
Fuse Holder - $0.61
1A Fuse - $0.32
Terminal Strip - $1.26

Total Cost - $15.04

You could also save the ten bucks on the PCB and duplicate this on a perforated board with minimal effort.

As with the V1.3, any normally closed (on when down) floatswitch can be used. I personally use and recommend the Chicago Sensor FLT015 - $7.00.



For my fellow Canadians - you will need to use a different relay, as the relay above is not in stock on digikey.ca

Canadian Relay - $2.39.

You'll also find that the prices on all of the other components are slightly higher, though that's not a surprise, is it?

Digikey has some weird script for determining which site to show you - the links to the parts are the same, but you must first go to www.digikey.ca and leave the tab open before clicking the links.

Great DIY here!

I can't believe I'm the first comment... Hopefully this isn't like a no comment thread or something...

Once I finish my tank I'll be setting up an ATO. I'm not sure exactly how I'll do it, but I will be making a simple 10g reservoir underneath my tank and I will probably use an aqualifter or a small powerhead. I would want 2 float switches in my sump (an extra switch slightly above in-case the first switch fails). I'm thinking it would also be a good idea to have a switch in the reservoir to keep my pump from running dry. Would the v1.3 accomodate this?

Also, how would you set the time delay?

No updates to this in some time so I hope I get a reply.

Did you build all three of these and test them or is this a "in theory" they shod work?