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Re: [Gumstix-users] Learning how to use GPIO
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From: Rizal N. <joe...@gm...> - 2009-04-05 05:04:26
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Thanks William, I think I understand now. I tried wiring up the circuit too, and it works great. On Sat, Apr 4, 2009 at 9:38 PM, William Hue <wi...@ne...>wrote: > Hi Joey, > > Yes. If you use a GPIO to drive the base of a transistor, and the > transistor activates the relay, that would work. You need a base resistor > to limit the current base current, and a reverse-biased diode across the > relay coil to absorb the inductive voltage spike that occurs when the > transistor turns off (or else the transistor will be damaged when you shut > off the relay). Here are some example circuits: > > http://letsmakerobots.com/node/4285 > > The third circuit shown in that webpage actually shows what I meant about > using the 2N4401 to get more voltage for the MOSFET's gate. > > William > > > Rizal Nor wrote: > > Thanks William, > > > > Even half awake you can still give good advise:). > > My circuits knowledge is limited so let me see if I understand you > > correctly. > > As I understand the GPIO can drive a source at 3ma/10ma. This is not > > enough if I would like to have a transistor like 2N4401 reach full > > saturation. Which mean that I won't be able to amplify the current to > > drive something that requires 400mA. Am I correct. However, it should be > > enough for a relay wouldn't it? > > > > So you are recommending that I use a mosfet with a 2N4401in > > common-emitter inverted configuration so that i can achieve higher > > currents...right > > > > On Sat, Apr 4, 2009 at 12:39 PM, William Hue <wi...@ne... > > <mailto:wi...@ne...>> wrote: > > > > Please see clarification below. > > > > William Hue wrote: > > > 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...> > > >> <mailto: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. > > > > Sorry, I am still sleepy this morning. Emitter-follower > > configuration would only provide GPIO voltage minus VBE. To provide > > more voltage at the gate of the MOSFET, the 2N4401 must be in > > common-emitter inverting configuration. Sorry about that. > > > > > > > >> > > >> > > >> > > >> -- > > >> Dave Hylands > > >> Shuswap, BC, Canada > > >> http://www.DaveHylands.com/ > > >> > > >> > > >> > > > ------------------------------------------------------------------------------ > > >> > > >> _______________________________________________ > > >> gumstix-users mailing list > > >> gum...@li... > > <mailto:gum...@li...> > > >> <mailto: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... > > <mailto:gum...@li...> > > >> https://lists.sourceforge.net/lists/listinfo/gumstix-users > > > > > > > > ------------------------------------------------------------------------------ > > _______________________________________________ > > 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 > > > > ------------------------------------------------------------------------------ > _______________________________________________ > gumstix-users mailing list > gum...@li... > https://lists.sourceforge.net/lists/listinfo/gumstix-users > -- Joey aka. Rizal Home is where people think of you... |