From: William H. <wi...@ne...> - 2009-04-04 16:35:41
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Hi Joey, please see my comment below. Rizal Nor wrote: > Hi Dave, > Thank you for the quick reply again. > > On Fri, Apr 3, 2009 at 11:14 PM, Dave Hylands <dhy...@gm... > <mailto:dhy...@gm...>> wrote: > > Hi Joey, > > > I know i need a mosfet circuit to drive the relay. But what I'm > not sure > > whether i need > > a relay in the first place. My device has a maximum load of > 400ma. According > > to tutorial sites you gave me, the ULN2803 can drive up to 500ma. > > Should I still get a relay, or should i just drive it directly > from the > > mosfet? > > It really depends on the type of thing that you're controlling. Is it > inductive? or resistive? > > > I want to control a satellite modem and a DO sensor. > I'm not sure if its inductive or resistive. > > > > What voltage does your load require? Presumably your load needs DC > rather than AC? > > > The DO sensor is using 12 volts. > And the satellite modem at 5 volts. > > As for now, the ULN2803 takes a while to get here. I'm going to use > 2N4401 that > i get from radioshack. It looks like this transistor can handle up to 600mA. > I'm going to go for the relay switch option for now, unless you advise > otherwise. > Do you see any problems for using this transistor? To assure good saturation, you need 40 mA of base current at Ic=400 mA. I doubt the Gumstix GPIO pin can supply this directly, and even if it could, it would not be good for it. I would use a MOSFET instead, but you need to either use a logic-level MOSFET or you can use the 2N4401 as an emitter-follower to provide approx. 12 V at the gate of the MOSFET. > > > > -- > Dave Hylands > Shuswap, BC, Canada > http://www.DaveHylands.com/ > > ------------------------------------------------------------------------------ > _______________________________________________ > gumstix-users mailing list > gum...@li... > <mailto:gum...@li...> > https://lists.sourceforge.net/lists/listinfo/gumstix-users > > > > > -- > Joey aka. Rizal > Home is where people think of you... > > > ------------------------------------------------------------------------ > > ------------------------------------------------------------------------------ > > > ------------------------------------------------------------------------ > > _______________________________________________ > gumstix-users mailing list > gum...@li... > https://lists.sourceforge.net/lists/listinfo/gumstix-users |