Aaron, The solenoid is an inductor, so it takes time for the current to ramp up once the voltage is applied (V=L di/dt, so the slope of the current rise is V/L. Increasing V makes the current ramp up faster while increasing L makes it ramp up more slowly. If there were no resistance in the inductor, the current would ramp up for ever, reaching infinite current in infinite time. The resistance of the inductor limits the current. As we approach the limit, the ramp gets less steep, giving us the familiar exponential curve). With the suggested circuit, the current in the solenoid ramps up when the transistor is on, then ramps down through the diode when the transistor is off. The average current is the same as if you'd applied 1.2V to the solenoid. The frequency of the PWM is normally chosen to be a little above audible (maybe 30 kHz) so the noise doesn't bother you (but may bother dogs). In this case, the lower limit to the frequency (other than it being audible) is probably pretty low since I believe we're dealing with heating effects instead of core saturation. Anyone have any better ideas on choosing the PWM frequency? Harold On Tue, 23 Jul 2002 14:59:16 -0400 "A.J. Tufgar" writes: > Harold, > I'm still confused about one aspect in your solution. Did you > mean that I should keep the same solenoid if I PWM the valve or I > should > get a new one? > > If I do PWM this valve won't I put to much voltage (5V) to the coil, > once the PWM module goes high? I'm afraid I don't understand the > concept of PWM to change the output voltage. Does It somehow lower > the > voltage to 1.2V? > > I do love your solution though thank's alot. > > I'll add this information to the post. My valve works off of 1.2 @ > 100mA. How would I PWM this valve off of a 5V supply? Or how does > this > solution work? > > Thanks all, > Aaron > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com Reach broadcasters, engineers, manufacturers, compliance labs, and attorneys. Advertise at http://www.hallikainen.com/FccRules/ . ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/web/. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.