More to plumbing fixtures' power needs than just electronics

After reading Specs: Sometimes timing really is everything, which details the importance of nailing down your op amp power requirement specs on the power requirements, an EDN reader asked, "I have often wondered about the technology behind these new automatic plumbing fixtures.  You cover the IR drive current and timing requirements, 4 AA battery power source, but how about the solenoid drive requirements that must be in this system or the IR receiver?" Hmmm. Good question.

So I went back to Tim Regan, ace apps engineering manager at Linear Technology, who worked through the numbers for power consumption and how they can vary based on unspecified part characteristics and thus impact the power consumption for these battery-powered devices.

His reply: "We weren't involved with the solenoid power section so I don't know specifics. The lifetime of the plumbing fixture had to be 15 years or so, including everything. The 4 AA batteries were for the IR section for certain, and could also be for the solenoid power. I know there are some very low current solenoids available but this wasn't part of any discussions I had with the customer. I think the valves could be electrically triggered opened and hydro-mechanically closed to save energy."

It's easy as EEs to see the world through a filter of electronic control circuits, but at some point our designs usually interact with mechanical devices. Next up for this ongoing saga of electronic plumbing fixtures: Ultra-low-power solenoids.