hamilton@udel.edu (andrew hamilton) (11/07/90)
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. Thanks in advance, Andrew.
ftpam1@acad3.fai.alaska.edu (MUNTS PHILLIP A) (11/07/90)
In article <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. > >Thanks in advance, > >Andrew. Here is one of my favorites. It should work from less than 1 Hz to several MHz, depending on the chip used and the resistor and capacitor. The order of magnitude of the frequency will be 1/RC. Stability and spectral purity is not very good, but it makes a decent digital system clock. R _____/\/\/\_____ | | | |\ | | | \ | | | \ | | | \ | | | \ | |-----| O---------> Output | | / | | / __|__ | / 74C14, 74HC14, etc. C _____ | / | |/ Not 74C04, 74HC04, etc. __|__ / / / A TTL 7414 can also be used but component values are more critical.
misra@matt.ksu.ksu.edu (11/07/90)
In article <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. > >Thanks in advance, > >Andrew. Are you sure about that? I have seen sch using the 555 and i think if you change the caps you get it going in the MHZ range. ************************************************************************* * * * * - I will put in something * Brijesh Misra * * soon * * ********************************** misra@ksuvm.ksu.edu * * FOR RENT * misra@matt.ksu.ksu.edu * * * * *************************************************************************
mark@mips.COM (Mark G. Johnson) (11/07/90)
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}
henry@zoo.toronto.edu (Henry Spencer) (11/08/90)
In article <1990Nov6.222448.15507@maverick.ksu.ksu.edu> misra@matt.ksu.ksu.edu writes: > Are you sure about that? I have seen sch using the 555 >and i think if you change the caps you get it going in the MHZ range. Bear in mind that 555s from different manufacturers may have somewhat different characteristics. It's entirely possible that *his* won't run at MHz speeds. -- "I don't *want* to be normal!" | Henry Spencer at U of Toronto Zoology "Not to worry." | henry@zoo.toronto.edu utzoo!henry
umapu02@cc.ic.ac.uk (D.A.G. Gillies Supvsr Dr K.J. Bignell) (11/09/90)
In article <1990Nov6.212128.16965@hayes.ims.alaska.edu> ftpam1@acad3.fai.alaska.edu writes: >In article <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. >> >>Thanks in advance, >> >>Andrew. > > Here is one of my favorites. It should work from less than 1 Hz to several >MHz, depending on the chip used and the resistor and capacitor. The order of >magnitude of the frequency will be 1/RC. Stability and spectral purity is not >very good, but it makes a decent digital system clock. > > R > _____/\/\/\_____ > | | > | |\ | > | | \ | > | | \ | > | | \ | > | | \ | > |-----| O---------> Output > | | / > | | / > __|__ | / 74C14, 74HC14, etc. > C _____ | / > | |/ Not 74C04, 74HC04, etc. > __|__ > / / / A TTL 7414 can also be used but > component values are more critical. The problem with this circuit is that it has quite high sideband noise (that said, I use it in almost all low stability applications I need. It is great for multiplexing LED sticks for example).For slightly more dosh, this one works great, and it gives TTL levels up to 25 MHz.It ain't as complex as it looks. ______ +5V | \ / \ 'LS00 / ___ 1/4 'HC04 |_____| \ |\ _________ | | | & |O----> output _______| \ | |<----Co-ax cable |/ |__| | | | O-----------------/\/\/\/\--------| T1 |___/ | | / | |_________| R3 | |\ | |/ | __|__ | | | R1 | ___ ___|___ | |___/\/\/\___| _ / \ __|__ | | 1N914 / \ ___ | \ ----- _ | / R2 | | \ | | __ / __|__ | || X|| | ___ |---|| L||---| _ | || 1|| | | -- | __|__ __|__ __ __ C1 __ __ C2 | | | | __|__ __|__ ___ ___ _ _ R1 = 10M R2 = 100k R3 = 1k R4 = 1k all metal film ( I use 0.6W,1% simply because they are the cheapest I can get) C1 = 20pF C2 = 20pf trimmer (frequency adjust) XL1 = crystal,100kHz to 28MHz (higher frequency may be dodgy) The co-ax cable is simply a way of moving RF around the PCB.It can probably be omitted for certain applications.The frequency variability is not very high (a few ppm) but can be divided with logic to give a very wide range of frequencies.I would recommend the 74LS292 and 74LS294 programmable frequency dividers.The '292 divides the input frequency by 2 to the power n,where n is a number from 2 to 31. Alternatively you could use cascaded 74167 BCD rate multipliers to generate a very accurately settable output in the Hz to MHz range,but here you're talking about frequency generators,and that might be a little complex.It's still a very feasible option though. -- ___________________________________________________________________________ ----Saddam Hussein - nuke him 'till he glows, then shoot him in the dark--- ---(c) The Amazing Underwater Chocolate Christmas Cracker Motto Factory---- ---------------------------------------------------------------------------
richm@amc-gw.amc.com (Rich Moran) (11/09/90)
In article <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. Try a 74S124. It's a dual voltage-controlled oscillator. Typical Fmax is 85MHz, according to the TI data book. Rich -- ============================================= Rich Moran richm@amc.com =============================================
pepke@gw.scri.fsu.edu (Eric Pepke) (11/10/90)
In article <3978@amc-gw.amc.com> richm@amc-gw.amc.com (Rich Moran) writes: > Try a 74S124. It's a dual voltage-controlled oscillator. Typical Fmax is > 85MHz, according to the TI data book. That's pretty good. Does anybody know of a VCO that will go up to 110 MHz? Or alternately, a good source of 110 MHz crystals and an oscillator circuit that will drive them? I just need a tiny deviation from 110 MHz, so a little variable capacitor might be all that is needed. Eric Pepke INTERNET: pepke@gw.scri.fsu.edu Supercomputer Computations Research Institute MFENET: pepke@fsu Florida State University SPAN: scri::pepke Tallahassee, FL 32306-4052 BITNET: pepke@fsu Disclaimer: My employers seldom even LISTEN to my opinions. Meta-disclaimer: Any society that needs disclaimers has too many lawyers.
grayt@spock (Tom Gray) (11/13/90)
In article <1376@sun13.scri.fsu.edu> pepke@gw.scri.fsu.edu (Eric Pepke) writes: > >That's pretty good. Does anybody know of a VCO that will go up to 110 >MHz? Or alternately, a good source of 110 MHz crystals and an oscillator Check out the Motorola ECL catalogs. The ECL VCO's will operate at above 100Mhz and will be very stable and controllable with +5V. To avoid other questions about ECL's. The VCO's will work on +5V without any problems.
henry@zoo.toronto.edu (Henry Spencer) (11/14/90)
In article <3978@amc-gw.amc.com> richm@the-end.amc.com (Rich Moran) writes: >Try a 74S124. It's a dual voltage-controlled oscillator. Typical Fmax is >85MHz, according to the TI data book. NO! NO! NO! The S124 is worthless junk! I speak from experience. If you must use a 7400-series part, look for (I think) 74S624. That's a version that's been fixed to work. I don't swear to the part number, as my references are at home and it's been a while. The part you want for fairly high-frequency VCOs, actually, is the MC4024. Beware, this is not a CMOS part, it is a TTL part with an odd number; the Motorola part number for the CMOS part that others would call "4024" is MC14024. You can often find the MC4024 in the "odds and ends" sections of catalogs. -- "I don't *want* to be normal!" | Henry Spencer at U of Toronto Zoology "Not to worry." | henry@zoo.toronto.edu utzoo!henry
henry@zoo.toronto.edu (Henry Spencer) (11/14/90)
In article <1376@sun13.scri.fsu.edu> pepke@gw.scri.fsu.edu (Eric Pepke) writes: >... Does anybody know of a VCO that will go up to 110 MHz? I had cause to look into this a few years ago; at that time, the answer was "welcome to the warm world of ECL". Such parts do exist, but they are not particularly easy to work with. The MC1658 was, at the time, grand champion of the VCO chips. -- "I don't *want* to be normal!" | Henry Spencer at U of Toronto Zoology "Not to worry." | henry@zoo.toronto.edu utzoo!henry
tell@oscar.cs.unc.edu (Stephen Tell) (11/14/90)
I don't know if its cheap, but the 1989 _Signetics Linear Data Manual Volume 1: Communications_ has a chip called the NE568, called a "150 Mhz Phase locked loop." One component of a PLL is, of course, a VCO. It looks like you should be able to use the VCO alone if want, although the output would probably need some work to get to a logic signal. Anybody know if this chip is any good? While we're talking PLL's, does anyone have any suggestions on chips or other approaches to using a PLL as a frequency synthesizer to generate 50 and 25 Mhz ECL clocks that are in phase with an incomming 25Mhz ECL clock? We'd prefer the clocks to stay pretty close to the rated values even when the input clock goes away, although the system really doesn't have to function that way, so I suppose a VCXO is in order. We need to clock in the incomming data from the interface cable at 25Mhz and run some control logic at 50Mhz. All the incomming signals are differential ECL, but we're planning to convert to TTL right away, with the possible exception of the clock generation/ distribution stuff. Thanks for any suggestions. -------------------------------------------------------------------- Steve Tell e-mail: tell@wsmail.cs.unc.edu usmail: #5L Estes Park apts CS Grad Student, UNC Chapel Hill. 919 968 1792 Carrboro NC 27510