Path: utzoo!attcan!uunet!ginosko!aplcen!uakari.primate.wisc.edu!uwm.edu!csd4.csd.uwm.edu!duc From: duc@csd4.csd.uwm.edu (D. Tran) Newsgroups: sci.electronics Subject: 555 IC Timer help needed Message-ID: <169@uwm.edu> Date: 23 Sep 89 06:02:07 GMT Sender: news@uwm.edu Reply-To: duc@csd4.csd.uwm.edu (Duc Minh Tran) Organization: University of Wisconsin-Milwaukee Lines: 48 Greetings, I have a simple question that I'm sure someone can answer. I'm building a simple circuit that contains a 555 IC timer chip. Vcc |__________ | | / __|__ R = resistor (R1) __|_____|__ C = capacitor \____| 4 8 | | |7 | (Output) __ __ / | 3|---------> __| |__| |__ (R2) | (555) | \____| TIMER | | + |2 | | |__| | | |6 1 5|---> ??? -+- |_____+_____| (C1) __|__ -+- --- __|__ GND --- GND Where Vcc = 5 volts Pin 1 = ground Pin 5 = control voltage Current = 125 mA 2 = trigger 6 = threshold 3 = output 7 = discharge 4 = reset 8 = + Vcc 1) How do I find the values for R1, R2, and C1? Is there a formula [ie. C1 (R1 + R2)...] 2) Can I replace R2 with a potentiometer so I can variate the output timing (ie. speed it up or slow it down). 3) What does pin #5 get hooked up to? BTW, I'm trying to hack together a rapid fire device for my joystick with my little knowlege of this type of circuit. I figured I can replace R2 with a pot. to be able to acomplish the rapid fire action. I would apprciate anybody with knowlege of this kind of stuff can help me out. I'm stumped right here...please email so we don't offend anyone. Thankyou. PS, sorry if this is not the appropriate newsgroup to post in.