Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!rochester!ken From: ken@cs.rochester.edu (Ken Yap) Newsgroups: sci.electronics Subject: Re: 555 IC Timer help needed Message-ID: <1989Sep26.024016.19124@cs.rochester.edu> Date: 26 Sep 89 02:40:16 GMT References: <169@uwm.edu> <568@limbic.UUCP> Reply-To: ken@cs.rochester.edu Organization: U of Rochester, CS Dept, Rochester, NY 14627, (716) 275-1448 Lines: 28 |> Vcc |> |__________ |> | | |> / __|__ |> R = resistor (R1) __|_____|__ |> C = capacitor \____| 4 8 | |> | |7 | (Output) __ __ |> / | 3|---------> __| |__| |__ |> (R2) | (555) | |> \____| TIMER | |> | + |2 | |> | |__| | |> | |6 1 5|---> ??? |> -+- |_____+_____| |> (C1) __|__ |> -+- --- |> __|__ GND |> --- |> GND | |Also note that, although I don't see it in this data sheet, that in all |other places I've read it is unwise to make R1 any smaller than 1K ohm. I |may be wrong about this, but I thought I read it somewhere. It's probably |a good rule of thumb. There a simple reason for this: pin 7 leads to an internal transistor that turns on to discharge C1 via R2. If you make R1 too small you will send too much current through this transistor and fry it.