jim@trsvax.UUCP (01/15/89)
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