Kathy That what i thought >>>>>1388 - 1389 Tal -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Kathy Quinlan Sent: Wednesday, March 06, 2002 6:47 PM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [EE]: didn't get it ! please help ----- Original Message ----- From: "K|bek Tony" To: Sent: Wednesday, March 06, 2002 11:18 PM Subject: Re: [EE]: didn't get it ! please help > Hi, > Tal wrote: > > >diode drops or 12-1.4 = 10.6. The resistor value will be the > voltage/current > >= 10.6/0.003 = 3533 or about 3.6K. The capacitor value for a 15 second > delay > >will be 15/3R = 1327 uF. We can use a standard 1000 uF capacitor and > >increase the resistor proportionally to get 15 seconds. " > > > > > >how he gets the value "1327 uF"?????? !!!!! > > > hmm...*read* the formula :) It states that the resistor value > is calculated as: voltage/current = 10.6/0.003 = 3533 ohm or approx. > 3.6K, now resistors are normally referred to as 'R' :) in the next statement > you have the conclusion that the capacitor should be calculated as: > Time/3*R so in essence it mean that the capacitor value would be > ( for 15 sec delay ) : 15/3*R = 15/3*3.6K = 15/10.8K = 1327uF presto ! > I am a little rusty as RC time constants were a 1'st year subject, some 11 years ago (gee how time flies) Am I missing something ?? T/(3R) = C T is in seconds R is in ohms C is in farads so : 15/10,800 = 0.001389 (in farads) so it is 1389mF (milli farads) = 1,389,000 uF ?? Regards, Kat. ____________________________________________________________________________ /"\ ASCII Ribbon Campaign | K.A.Q. Electronics \ / - NO HTML/RTF in e-mail | Software and Electronic Engineering X - NO Word docs in e-mail | Perth Western Australia / \ | Ph +61 419 923 731 ____________________________________________________________________________ -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body