--_003_201202091909q19J9IEA007208mailhubdmz4mitedu_ Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable PS: please could you take a look at this LTSpice IV circuit in attachment? I think I applied the idea correctly, but it seems that it's not rejecting the noise that I capacitively couple with the signal. :( What I want is to detect when the input signal goes a threshold above zero volts (say 1.3V), and when it goes below (say -1.3V). The circuit seems to work perfectly (gives 2 digital negated outputs), but it doesn't seem to reject common noise at all, that's the problem. As you probably know, I've been struggling with this input circuit (designe= d 5 different ones (single ended, optocoupled, differential, weird and one ev= en more strange) for many months now, without ever being able to select a best performing one. Transistor count has to be as low as possible, this is the main contraints, but also total component count should be low, and the powe= r supply must be +3.3V single supply. With kind regards, Mario >At 10.06 2012.02.09, you wrote: >>> I need to design a device that interfaces to the speed sensor of heavy >>> trucks. These are variable reluctance sensors and will remain connected >>> to the vehicle's ECU, my circuit will piggyback. These are two-wire, >>> differential signals full of common-mode noise and vary in amplitude >>> greatly with frequency and also position as the tailshaft bearing wears >>> in the vehicle. >> >>I had a similar but totally different [tm] application whose solution >>may be your solution. >> >>I had a variable speed alternator (exercise machine load) whose out >>put was a low voltage sinusoid at low speeds but which soon chose to >>flat topped trapezoids clamped to the mean load voltage. As this >>voltage varied depending on speed and net absolute load desired it >>would have been modestly challenging to speed sense from. Now add 10 >>kHz PWM that takes a fixed resistor and PWM's it across the rectified >>alternator output to change the effective resistance seen by the >>alternator. Yee ha. >> >>After trying all sorts of things I was offended by the simplicity of >>what proved to be a superb solution. >>Stops to find a circuit from about 10 years ago ... >>.... Found ... >>Hmmm. May 18th 2006. More recent than I would have thought. >> >>2 x BC337 or whatever >>Differential long tailed pair. >>100k collector resistor per transistor. >>Join emitters with 1k to ground, >>Input drive to each base via a 100k (one per base :-) ). > >Like this, but with the base resistors? > >http://upload.wikimedia.org/wikipedia/commons/1/15/Difference_amplifier.pn= g > > >>Two drive inputs connect across an alternator winding. > >The 2 wires from the sensor go to the bases (through 100k resistors), but >there must be a third leg to ground.. to reference the two signals? > > >>Diagram shows base to ground resistors per transistor but notes that >>they are O/C. > >O/C =3D ? > > >>That's it !!! >>Probably Vcc =3D 5V. (Murphy says the value is on the sheet I didn't >>load BUT probably 5V). > >-V (in the pic I linked above) is ground, or needs negative supply? > >Cheers, >Mario > > >>Alternator is 4 phase custom built. Max output > 200 VAC. >> >>Speed output taken from collector of your choice. >> >>This is "offensive" in that (at least) it does not explicitly deal >>with the 10 kHz PWM or the sometimes very low voltage and max voltages >>of say 300 V peak are applied to transistor bases directly with no >>attempt to limit voltage or current (apart from the obvious ways in >>which the transistors do this. Ibase max=3D 3 mA worst case but usually >>much less than that. >> >>The "magic" lies in the differential pair. >>It performs as a superb comparator. >> >>Noise immunity MAY be aided by the driving of base junctions deeply >>into saturation. Ib > to >> Ic in most cases. >> >>As I recall, along the way I used 3 or 4 pole Bessel low pass filters >>using 1 or 2 emitter followers to provide a low cost filter. This >>was extremely effective at removing PWM but not needed for the long >>tailed pair solution. >> >> >> >> Russell McMahon --_003_201202091909q19J9IEA007208mailhubdmz4mitedu_ Content-Type: text/plain; name="differential.asc" Content-Description: differential.asc Content-Disposition: attachment; filename="differential.asc"; size=3133; creation-date="Thu, 09 Feb 2012 11:15:06 GMT"; modification-date="Thu, 09 Feb 2012 11:15:06 GMT" Content-Transfer-Encoding: base64 VmVyc2lvbiA0DQpTSEVFVCAxIDE2OTYgNzM2DQpXSVJFIC01MjggLTM4NCAtMTUzNiAtMzg0DQpX SVJFIC0zNjggLTM4NCAtNTI4IC0zODQNCldJUkUgMjg4IC0zODQgLTM2OCAtMzg0DQpXSVJFIC01 MjggLTMzNiAtNTI4IC0zODQNCldJUkUgLTM2OCAtMzM2IC0zNjggLTM4NA0KV0lSRSAtMzY4IC0x OTIgLTM2OCAtMjU2DQpXSVJFIDI4OCAtMTkyIC0zNjggLTE5Mg0KV0lSRSAtNTI4IC05NiAtNTI4 IC0yNTYNCldJUkUgMjg4IC05NiAtNTI4IC05Ng0KV0lSRSAtMTI0OCAtODAgLTEzNjAgLTgwDQpX SVJFIC05MjggLTgwIC0xMjQ4IC04MA0KV0lSRSAtODY0IC04MCAtOTI4IC04MA0KV0lSRSAtMTM2 MCAtNjQgLTEzNjAgLTgwDQpXSVJFIC01MjggLTE2IC01MjggLTk2DQpXSVJFIC0zNjggLTE2IC0z NjggLTE5Mg0KV0lSRSAtMTM2MCAzMiAtMTM2MCAxNg0KV0lSRSAtODY0IDMyIC04NjQgLTgwDQpX SVJFIC02NzIgMzIgLTg2NCAzMg0KV0lSRSAtNjQgMzIgLTIyNCAzMg0KV0lSRSAtMTM2MCAxMjgg LTEzNjAgMTEyDQpXSVJFIC01MjggMTkyIC01MjggODANCldJUkUgLTQ0OCAxOTIgLTUyOCAxOTIN CldJUkUgLTM2OCAxOTIgLTM2OCA4MA0KV0lSRSAtMzY4IDE5MiAtNDQ4IDE5Mg0KV0lSRSAtMTM2 MCAyMjQgLTEzNjAgMjA4DQpXSVJFIC0xMzEyIDIyNCAtMTM2MCAyMjQNCldJUkUgLTEwMjQgMjI0 IC0xMzEyIDIyNA0KV0lSRSAtNjQgMjI0IC02NCAzMg0KV0lSRSAtNjQgMjI0IC0xMDI0IDIyNA0K V0lSRSAtMTMxMiAzMDQgLTEzMTIgMjI0DQpXSVJFIC0xMjQ4IDMwNCAtMTI0OCAtODANCldJUkUg LTEwMjQgMzM2IC0xMDI0IDIyNA0KV0lSRSAtOTI4IDMzNiAtOTI4IC04MA0KV0lSRSAtNDQ4IDM1 MiAtNDQ4IDE5Mg0KV0lSRSAtMTMxMiA0MDAgLTEzMTIgMzY4DQpXSVJFIC0xMjgwIDQwMCAtMTMx MiA0MDANCldJUkUgLTEyNDggNDAwIC0xMjQ4IDM2OA0KV0lSRSAtMTI0OCA0MDAgLTEyODAgNDAw DQpXSVJFIC0xNTM2IDQzMiAtMTUzNiAtMzg0DQpXSVJFIC0xMjgwIDQzMiAtMTI4MCA0MDANCldJ UkUgLTE1MzYgNTQ0IC0xNTM2IDUxMg0KV0lSRSAtMTI4MCA1NDQgLTEyODAgNTEyDQpXSVJFIC0x MjgwIDU0NCAtMTUzNiA1NDQNCldJUkUgLTEwMjQgNTQ0IC0xMDI0IDQxNg0KV0lSRSAtMTAyNCA1 NDQgLTEyODAgNTQ0DQpXSVJFIC05MjggNTQ0IC05MjggNDE2DQpXSVJFIC05MjggNTQ0IC0xMDI0 IDU0NA0KV0lSRSAtNDQ4IDU0NCAtNDQ4IDQzMg0KV0lSRSAtNDQ4IDU0NCAtOTI4IDU0NA0KV0lS RSAzMDQgNTQ0IC00NDggNTQ0DQpXSVJFIC00NDggNTc2IC00NDggNTQ0DQpGTEFHIC00NDggNTc2 IDANClNZTUJPTCBucG4gLTMwNCAtMTYgTTANClNZTUFUVFIgSW5zdE5hbWUgUTENClNZTUFUVFIg VmFsdWUgMk4zOTA0DQpTWU1CT0wgdm9sdGFnZSAtMTM2MCAxNiBSMA0KV0lORE9XIDEyMyAwIDAg TGVmdCAyDQpXSU5ET1cgMzkgMCAwIExlZnQgMg0KV0lORE9XIDMgMjQgOTYgSW52aXNpYmxlIDIN ClNZTUFUVFIgVmFsdWUgUFdMKDAgMCAuMDAxIC0yMCAuMDAyIDAgLjAwNyAwIC4wMDggKzIwIC4w MDkgMCkNClNZTUFUVFIgSW5zdE5hbWUgVjENClNZTUJPTCB2b2x0YWdlIC0xNTM2IDQxNiBSMA0K V0lORE9XIDEyMyAwIDAgTGVmdCAyDQpXSU5ET1cgMzkgMjQgMTI0IExlZnQgMg0KU1lNQVRUUiBJ bnN0TmFtZSBWMg0KU1lNQVRUUiBWYWx1ZSAzLjMNClNZTUJPTCByZXMgLTEzNzYgLTgwIFIwDQpT WU1BVFRSIEluc3ROYW1lIFI4DQpTWU1BVFRSIFZhbHVlIDE3MA0KU1lNQk9MIHJlcyAtMzUyIC0y NDAgUjE4MA0KV0lORE9XIDAgMzYgNzYgTGVmdCAyDQpXSU5ET1cgMyAzNiA0MCBMZWZ0IDINClNZ TUFUVFIgSW5zdE5hbWUgUjMNClNZTUFUVFIgVmFsdWUgMTAwaw0KU1lNQk9MIHJlcyAtNTEyIC0y NDAgUjE4MA0KV0lORE9XIDAgMzYgNzYgTGVmdCAyDQpXSU5ET1cgMyAzNiA0MCBMZWZ0IDINClNZ TUFUVFIgSW5zdE5hbWUgUjENClNZTUFUVFIgVmFsdWUgMTAwaw0KU1lNQk9MIHZvbHRhZ2UgLTEy ODAgNDE2IFIwDQpXSU5ET1cgMTIzIDAgMCBMZWZ0IDINCldJTkRPVyAzOSAwIDAgTGVmdCAyDQpX SU5ET1cgMyAyNCA5NiBJbnZpc2libGUgMg0KU1lNQVRUUiBJbnN0TmFtZSBWMw0KU1lNQVRUUiBW YWx1ZSBTSU5FKDEwIDUgNTAwMCkNClNZTUJPTCBjYXAgLTEzMjggMzA0IFIwDQpTWU1BVFRSIElu c3ROYW1lIEMxDQpTWU1BVFRSIFZhbHVlIDEwMHANClNZTUJPTCBjYXAgLTEyNjQgMzA0IFIwDQpT WU1BVFRSIEluc3ROYW1lIEMyDQpTWU1BVFRSIFZhbHVlIDEwMHANClNZTUJPTCBucG4gLTU5MiAt MTYgUjANClNZTUFUVFIgSW5zdE5hbWUgUTINClNZTUFUVFIgVmFsdWUgMk4zOTA0DQpTWU1CT0wg cmVzIC00MzIgNDQ4IFIxODANCldJTkRPVyAwIDM2IDc2IExlZnQgMg0KV0lORE9XIDMgMzYgNDAg TGVmdCAyDQpTWU1BVFRSIEluc3ROYW1lIFI2DQpTWU1BVFRSIFZhbHVlIDFrDQpTWU1CT0wgcmVz IC0xMDQwIDMyMCBSMA0KU1lNQVRUUiBJbnN0TmFtZSBSNA0KU1lNQVRUUiBWYWx1ZSAxMDAwaw0K U1lNQk9MIHJlcyAtOTQ0IDMyMCBSMA0KU1lNQVRUUiBJbnN0TmFtZSBSNQ0KU1lNQVRUUiBWYWx1 ZSAxMDAwaw0KU1lNQk9MIHJlcyAtNTc2IDE2IFI5MA0KV0lORE9XIDAgMCA1NiBWQm90dG9tIDIN CldJTkRPVyAzIDMyIDU2IFZUb3AgMg0KU1lNQVRUUiBJbnN0TmFtZSBSMg0KU1lNQVRUUiBWYWx1 ZSAxMDBrDQpTWU1CT0wgcmVzIC0yMDggMTYgUjkwDQpXSU5ET1cgMCAwIDU2IFZCb3R0b20gMg0K V0lORE9XIDMgMzIgNTYgVlRvcCAyDQpTWU1BVFRSIEluc3ROYW1lIFI3DQpTWU1BVFRSIFZhbHVl IDEwMGsNClNZTUJPTCByZXMgLTEzNzYgMTEyIFIwDQpTWU1BVFRSIEluc3ROYW1lIFI5DQpTWU1B VFRSIFZhbHVlIDE3MA0KVEVYVCAtMzM2IDYwMCBMZWZ0IDIgIS50cmFuIDAgMC4wMTA4IDAgMC4w MDAwMDAxDQpURVhUIC0xNDcyIDcyIExlZnQgMiA7c2lnbmFsDQpURVhUIC0xNjQ4IDQ2NCBMZWZ0 IDIgO3Bvd2VyDQpURVhUIC0xMzg0IDQ3MiBMZWZ0IDIgO25vaXNlDQpURVhUIDE5MiAtMjI0IExl ZnQgMiA7b3V0cHV0IDENClRFWFQgMTkyIC0xMjggTGVmdCAyIDtvdXRwdXQgMg0K --_003_201202091909q19J9IEA007208mailhubdmz4mitedu_ Content-Type: text/plain; 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