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RO Water Controller - Overview of Controller Design <<< Previous Next >>>

I did have very basic understanding of electronics from my youth. This aided me in the design of controller, which incidentally is my first electronic project. However much of my time over last few months was spent researching how to put together circuits and functions of components. I am sure someone with more knowledge of electronics will look at my circuits and say that there is an easier way. I used a number of web sites extensively during my research, the main ones being Kelsey Park School and Play-Hookey Website. I found that these gave me enough knowledge to put together the circuits. Both are excellent sites and certainly worth a look for anybody who is interested.

After a number of wrong turns I finally used Eagle Layout Editor by Cadsoft. This is freeware for non-profit use and can be downloaded from All the circuit diagrams and PCB layouts on this website are for use in this editor. The restriction in the freeware version is the size of boards that you can design.

I decided at an early stage that I would put the functions of controller in modules. This enabled me to build a specific area using protyping boards (or breadboards) and test it. Once tested I created the PCB, soldered on the components and used that board replacing the protyping board to connect the other boards or protyping boards of the controller. However I didn't do this with the relay board as I didn't fancy playing with mains electrics. That was the last board I designed and built. I built this without protyping and I was lucky it worked first time.

For those who don't know a protyping board or breadboard is used for testing or trying out ideas. There is no soldering required and you can easily remove and replace components. These come in many sizes and configurations.

BImage of Breadboard

Some of my functional boards do not include all the components of the specific function i.e. what I am calling the 'Drain Timer Board'. This has some of the components such as NE555 timer chip, relevant capacitors etc situated on the 'Main board'. This just how I put the components together on the protyping boards.

Creating small functions also fitted in nicely with the fact that Eagle software had a restriction on board size. The basic functions I split into boards are as follows:-

Power Supply - supplies a 12V clean voltage with the ability draw 1A of current.

Main Board - Uses the float switch signals as inputs and sends signals to the relay board to power relays which drive the solenoid valves. It also receives inputs from the drain timer board, and sends signals to LED Front Panel to power LED to signify various states.

LED Counter Display - LED display to count the number of times the controller has filled up the RO reservoir. There is also a reset switch on the controller to reset this count.

Battery Backup for the LED Counter Display - One of the problems with the LED counter is that it loses the count if there is a power cut. So this board in theory will swap over the power supply to a 9V battery in the event of a power cut. This seemed to work on the bench, but is not working correctly once I have put everything together. Something I need to investigate. During a power cut, the board also sets a power loss LED to signify that the count could be inaccurate.

LED Front Panel Indicators - Simple panel full of LED to signify various states such water level at the top float etc.

Drain Timer - Connected to the rotary switch on the front of the box to set the time to open the drain solenoid.

Relay - This board housed the relays to switch the various 12V solenoid valves and also the 240V relays to the switch the heater and top-up pump,

Image of overhead view of controller




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