Water Filter Controller

The old adage “measure twice, cut once” has a realitve in the field of electronics engineering; “measure twice, design once” … ok, well maybe that’s a bit corny but anyway.

Turns out the controller I designed for my water filter is pretty much useles. My filter’s pump is not the 12vdc that I imagined it to be, instead, it is 24vac. So the two smt mosfets which I soldered to my pcb with generous amounts of solder, are not capable of switching AC. Worse, I had planned to power the controller itself off the psu for the pump, so the 7805 vreg I’m using will not appericate AC on its input terminals either.

I plan to salvage this situation however… using relays, either mechanical or electronic, as well as a separate power supply. So, I will use a ~12 volt unregulated supply to power a pair of mechanical relays, one for the pump, one for the valve, which in turn will be switched by the mosfets. Or, I can desolder / destroy / jumper over the mosfets, and run a +5v control signal to my outputs, for control of a solid state relay.

I need to price out the cost of mechanical vs solid state …. probably solid state will win, I think I can build a triac based ssr for under $2.

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