Square + triangle = sine (almost)
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From: whit3rd on 7 Mar 2010 19:10 On Mar 6, 8:04 pm, rontan...(a)esterbrook.com (Ron Tanner) wrote: > On Sun, 7 Mar 2010 14:31:48 +1100, "Phil Allison" <phi...(a)tpg.com.au> > wrote: > >> If a squarewave contains all odd harmonics of the fundamental > >> frequency, and a triangle all even, > > > ** Sorry - that is WRONG . > > > A triangle wave contains only odd harmonics too. > OK thanks for the pull-up, but how about using a triangle-square wave > mix, in place of a filter, to simulate a sinewave . To generate a square wave and triangle wave together, just hook a Schmitt trigger to an op amp configured as integrator (resistor from input to (-) node, feedback capacitor from op amp output to (-) node. The output of the op amp then is fed to the Schmitt trigger (a '555 does this without the op amp, but its triangle waves are curvey because of that). The result is a square wave and a triangle wave, both of constant amplitude, which changes frequency with a single variable resistor (the integrator input resistor). SO, now you want to mix a square and triangle? If you generate them by the method above, fundamentals ARE OUT OF PHASE by ninety degrees, and so are all of the harmonics. You get neither cancellation nor reinforcement by any simple summing.
From: JosephKK on 8 Mar 2010 02:11 On Sat, 6 Mar 2010 20:21:10 -0800, D from BC <myrealaddress(a)comic.com> wrote: >In article <4b9324ee.4432562(a)news.tpg.com.au>, rontanner(a)esterbrook.com >says... >> >> On Sun, 7 Mar 2010 14:31:48 +1100, "Phil Allison" <phil_a(a)tpg.com.au> >> wrote: >> >> > >> >"Harold Larsen" >> >> >> >> If a squarewave contains all odd harmonics of the fundamental >> >> frequency, and a triangle all even, >> > >> > >> > ** Sorry - that is WRONG . >> > >> > A triangle wave contains only odd harmonics too. >> > >> >http://en.wikipedia.org/wiki/Triangle_wave >> > >> >A "sawtooth" wave contains all integer harmonics. >> > >> >> OK thanks for the pull-up, but how about using a triangle-square wave >> mix, in place of a filter, to simulate a sinewave . >> >> I have not seen that method applied or described anywhere, but it >> makes a fair approximation, at least to my eye. >> >> Harold Larsen > > >This reminds of the XR2206 chip that makes square, triangle and sine >using analog technology. Sure enough, as does the ICL8038. Part of the question is how it is done.
From: Muzaffer Kal on 8 Mar 2010 03:01 On Sun, 07 Mar 2010 23:11:20 -0800, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Sat, 6 Mar 2010 20:21:10 -0800, D from BC <myrealaddress(a)comic.com> wrote: > >>In article <4b9324ee.4432562(a)news.tpg.com.au>, rontanner(a)esterbrook.com >>says... >>> >>> On Sun, 7 Mar 2010 14:31:48 +1100, "Phil Allison" <phil_a(a)tpg.com.au> >>> wrote: >>> >>> > >>> >"Harold Larsen" >>> >> >>> >> If a squarewave contains all odd harmonics of the fundamental >>> >> frequency, and a triangle all even, >>> > >>> > >>> > ** Sorry - that is WRONG . >>> > >>> > A triangle wave contains only odd harmonics too. >>> > >>> >http://en.wikipedia.org/wiki/Triangle_wave >>> > >>> >A "sawtooth" wave contains all integer harmonics. >>> > >>> >>> OK thanks for the pull-up, but how about using a triangle-square wave >>> mix, in place of a filter, to simulate a sinewave . >>> >>> I have not seen that method applied or described anywhere, but it >>> makes a fair approximation, at least to my eye. >>> >>> Harold Larsen >> >> >>This reminds of the XR2206 chip that makes square, triangle and sine >>using analog technology. > >Sure enough, as does the ICL8038. Part of the question is how it is done. The datasheet at http://www.intersil.com/data/FN/FN2864.pdf has a pretty good schematic and explanation which shows how it's done. -- Muzaffer Kal DSPIA INC. ASIC/FPGA Design Services http://www.dspia.com
From: Tim Williams on 8 Mar 2010 03:44 "whit3rd" <whit3rd(a)gmail.com> wrote in message news:42d6a02a-ea10-492c-b6bc-d7c61d2b9f41(a)y17g2000yqd.googlegroups.com... > The output of the op amp then is fed to the Schmitt trigger (a '555 > does this without the op amp, but its triangle waves are curvey > because of that). You can use diode gates to divert a current source and sink into the cap, driving the gate with the output pin (since pin 7 doesn't source current). Then you also get freely adjustable frequency and duty cycle, like a proper function generator. Add a buffer and you've got a hearty triangle output! Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Frank-Stefan Müller on 8 Mar 2010 04:04
Phil Allison schrieb: > "Ron Tanner" > "Phil Allison" >>> "Harold Larsen" >>>> If a squarewave contains all odd harmonics of the fundamental >>>> frequency, and a triangle all even, >>> >>> ** Sorry - that is WRONG . >>> >>> A triangle wave contains only odd harmonics too. >>> >>> http://en.wikipedia.org/wiki/Triangle_wave >>> >>> A "sawtooth" wave contains all integer harmonics. >>> >> OK thanks for the pull-up, but how about using a triangle-square wave >> mix, in place of a filter, to simulate a sinewave . >> >> I have not seen that method applied or described anywhere, but it >> makes a fair approximation, at least to my eye. >> > > ** Maybe you need better eyes. > > Ever noticed how sine waves are flat topped and pass through zero at a 45 > degree angle ? In Gemany, the angle is 56.789 degrees, because the mains voltage is higher... Frank > > Not much like your hut with pitched roof wave....... > > > > ..... Phil > > > > |