Path: utzoo!utgpu!watserv1!watmath!att!att!pacbell.com!mips!hal!mark
From: mark@mips.COM (Mark G. Johnson)
Newsgroups: sci.electronics
Subject: Re: cheap hi-speed oscillator
Message-ID: <42869@mips.mips.COM>
Date: 7 Nov 90 03:06:07 GMT
References: <35596@nigel.ee.udel.edu>
Sender: news@mips.COM
Reply-To: mark@mips.COM (Mark G. Johnson)
Organization: MIPS Computer Systems, Inc.
Lines: 31

In <35596@nigel.ee.udel.edu> hamilton@udel.edu (andrew hamilton) writes:
   >
   >Anyone know how to make a cheap variable frequency oscillator that will
   >oscillate in the MHz range.  555's don't seem to be able to do more than
   >about 500KHz.
   >

For $0.35 Digi-Key will sell you a 74HC14.  How about hooking it up as
an ultra cheapo RC relaxation oscillator:

     +------------------------------------------------+
     |                                                |
     |     50K potentiometer                 +        |   +
     |                                       | \      |   | \
     +-----/\/\/\/\/\---+---------+----------|  >0----+---|  >0---- OUTPUT
                A       |         |          | /          | /
                |       |         |          +            +
                +-------+       -----
                                -----
                                  |   68pF
                                  |   capacitor
                                 GND

This ckt will top out around 12 MHz  (for faster still, reduce the cap
value and be more careful with layout).  Beware, the 74HC family works
from 2 to 6 volt supplies; unlike the old RCA family, these fellers
poop out and die at VCC=6.5V.
-- 
 -- Mark Johnson	
 	MIPS Computer Systems, 930 E. Arques M/S 2-02, Sunnyvale, CA 94086
	(408) 524-8308    mark@mips.com  {or ...!decwrl!mips!mark}