From: Jesse W. <jda...@ho...> - 2006-07-20 22:41:11
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I second that one (^^)v....Dave always Saves the day. -Jesse W. >From: "A.M. Sabuncu" <ams...@gm...> >Reply-To: "General mailing list for gumstix users." ><gum...@li...> >To: "General mailing list for gumstix users." ><gum...@li...> >Subject: Re: [Gumstix-users] GPIO input >Date: Thu, 20 Jul 2006 13:37:29 -0700 > >Dave, > >Thank you for a very clear explanation. > >There should be a Gumstix MVP program established, and I feel you should >get >to be the first one. > >Todd > >On 7/20/06, Dave Hylands <dhy...@gm...> wrote: >> >>Hi Todd, >> >> > > > That driver responds only to falling edges on the GPIO line, >>right? I'm >> > > > somewhat surprised that it would do this - it would be more >>generally >> > > > useful to respond to a falling or rising edge on the GPIO I would >>have >> > > > thought, but I guess it is just an example. >> > > >> > > Yes. The assumption was that the input is pulled high, and closing >>the >> > > switch connects the input to ground. >> > >> > Could you please elaborate about the part about input being pulled >>high, >>for >> > someone who does not have as much electronics knowledge? Thanks - >> >>So simple switches are normally of the momentary SPST (single pole >>single throw) variety. They're either closed (conducting) or open >>(non-conducting). >> >>If you connect one side of the switch to ground and the other side to >>your GPIO, that gives you a good solid ground connection when the >>switch is pushed. When the switch is not pushed, then the input is >>floating and the input will tend to follow other inputs around it (due >>to an effect called capacative coupling). >> >>So you typically add a resistor, commonly called a pull-up resistor, >>which pulls the input up to whatever the logic high voltage is. The >>resistor is typically 10k ohms or higher. >> >>Now when the switch is open, the resistor will pullup the signal to a >>logic high, rather than leaving it floating. >> >>You can also reverse things, and have the one side of the switch >>connected to the logic high voltage (say 3.3v) and the other side >>connected to the input. Now the resistor would connect between the >>input and ground, and it would be referred to as a pull-down resistor. >> >>In the days of TTL logic, almost all resistors were pullup, since TTL >>could do a really good job of driving a signal to ground and a not so >>goof job of pulling it high. >> >>In todays world, almost everything is CMOS, and CMOS can do just as >>good a job of pulling something high as low, so you can now do things >>more at your convenience, rather than the hardwares convenience. So >>choosing pullup or pulldown is rather arbitrary. >> >>-- >>Dave Hylands >>Vancouver, BC, Canada >>http://www.DaveHylands.com/ >> >>------------------------------------------------------------------------- >>Take Surveys. Earn Cash. Influence the Future of IT >>Join SourceForge.net's Techsay panel and you'll get the chance to share >>your >>opinions on IT & business topics through brief surveys -- and earn cash >>http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV >>_______________________________________________ >>gumstix-users mailing list >>gum...@li... >>https://lists.sourceforge.net/lists/listinfo/gumstix-users >> >------------------------------------------------------------------------- >Take Surveys. Earn Cash. Influence the Future of IT >Join SourceForge.net's Techsay panel and you'll get the chance to share >your >opinions on IT & business topics through brief surveys -- and earn cash >http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV >_______________________________________________ >gumstix-users mailing list >gum...@li... >https://lists.sourceforge.net/lists/listinfo/gumstix-users |