NT coughed up some electrons that declared:


Just had a call back from the designer (who I guess is also the owner).
Very interesting... They use a custom design latching solenoid valve,
driveable by pulse in the range of 6-24v. And he seems happy to sell the
valves on their own.

So I'd need a little interface timer that can apply the pulses based on a
general demand input (sounds like either a job for a 555 or an AVR/PIC
depending on your bent).

just wondering why a 555. All ac solenoids will run off dc, at IIRC
about half or 2/3 the voltage.


NT

Because it's a pulse driven latching jobbie.

The bloke said any attempt to continuously feed it will burn the coil out.

OK, 555 may be overkill, could probably do it by dumping a charged capacitor
into it using transistors to pump the charge through it.

I think this may be how the company use it - he mentioned using a 6.8mF
capacitor.

Anyway, with these valves, you bang a charge pulse through them one way to
turn on and the same charge through the opposite way to turn off. Do
nothing and they maintain their current state.

Me - it'd probably use a little 14 pin AVR microcontroller and as few
transistors as possible. They're like a quid, I'm setup to program them, I
can add a few failsafes (like if "call for water" is held high,
periodically send a refresher pulse to the valve every 10 minutes, just in
case it got stuck the first time (don't know if that ever happens), make
the valve "network" addressable too - RS485 being an easy choice) and any
other random funky stuff - probably all for a fiver, a bit of veroboard and
a little box all running off the 12V SELV supply that I need for other
things anyway.

Probably take a day or two to bang up a prototype that works.
And energy efficient to boot.

The only thing lacking is positive feedback that the valve is open or
closed,which is something you can of course have with a motorised zone
valve (mains operated at more cost too).
Cheers

Tim