🚀 go-pugleaf

icarus.eng.ohio-state.edu!borgstrm writes in sci.electronics:
" The valves would be used to control hot and cold water to a
" faucet or shower and thus can't be the solenoid type. I would like an
" inexpensive model that runs off 24 VDC or less and possibly has a built-in
" valve-position encoder.

The variable valves with servo motors (with or without feedback) are going
to be expensive - no other way to buy it. You could build your own, though.
If this is feeding a bath, you could make a PWM controller for a dual
electric valve from a dishwasher or washing machine. Feed the controller
the rate you want, the temp you want, and the temp of the output and let
it pulse the valves. The pulsing effect might be like a shower-massage(tm)
if the pulsing were quick enough. The system is fail-safe in that if the
power or solenoid fails, the water flow stops.

You could also go to a surplus parts house and get some servo motors, gears
potentiometer, and a valve. This is the harder route - you need a lot more
tools and time. It is good practice to use limit microswitches to stop the
motor at the ends of it's range. You could infer the position of the valve
if it is being driven by a uP. Measure the time it takes to close and open
and remember the elapsed time moving back and forth - resetting it when the
limit switch gets tripped. Not very accurate, but it's cheap and in
software - how accurately do you set you bath water anyway.

Even though you are using 24V valves, consider using an inexpensive ground
fault interrupter for the control unit's power feed. This protects the user
from the panel control faults as well as motor faults. Hope this helps!

James T. Wyatt  UUCP:decvax!microsoft!trsvax!rwsys!jim  KA5VJL