Post by thread:[EE]: Noise problem with schmidt trigger

I have a schmidt trigger connected to my microcontroller counting the number of pulses coming from the schmidt trigger. I notice that whenever any power supply is turned on (DC power supply unit, any step down transformer), the counter value jumps unpredictably. When I remove the input to the schmidt trigger(microcontroller to schmidt trigger wire is still there), everything is fine. I replace the input to the schmidt trigger with just a long wire and the problem appears again. It seems to me that the schmidt trigger has very low threshold value, to the extend that it interprets these noise as a signal. Is there anyway I can solve this problem? I thought of a rather stupid solution as to wrap the input wire to the schmidt wire with aluminium foil. Will it work? Thanks Mark _________________________________________________________________ Add photos to your messages with MSN 8. Get 2 months FREE*. http://join.msn.com/?page=features/featuredemail -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu>

It sounds like you have a fairly high input impedance to your schmitt trigger making it sensitive to electrical noise. If your circuit does not require high input impedance, try lowering it. What is connected to the input of the schmitt trigger? At 12:48 AM 5/12/03 +0000, you wrote: {Quote hidden}>I have a schmidt trigger connected to my microcontroller counting the number >of pulses coming from the schmidt trigger. I notice that whenever any power >supply is turned on (DC power supply unit, any step down transformer), the >counter value jumps unpredictably. When I remove the input to the schmidt >trigger(microcontroller to schmidt trigger wire is still there), everything >is fine. I replace the input to the schmidt trigger with just a long wire >and the problem appears again. > >It seems to me that the schmidt trigger has very low threshold value, to the >extend that it interprets these noise as a signal. Is there anyway I can >solve this problem? I thought of a rather stupid solution as to wrap the >input wire to the schmidt wire with aluminium foil. Will it work? > >Thanks >Mark > -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu>

Thanks for your reply. The input to my schmitt trigger is actually pulses coming from an optical encoder. 2 pulses of different phases are sent to my microcontroller via two schmitt trigger to decode the position of the motor. My microcontroller is configure as an event counter to count these pulses. I tried so many techniques but fail to find a solution to this problem. Whenever any equipment with transformer is switched on nearby, the counter jumps wildly. Being a rather lousy student myself, can you explain how can I lower the high input impedance to my schmitt trigger? The wire carrying the pulses from the optical encoder to the schmitt trigger is about 2meters long. Thanks alot! Mark {Quote hidden}>From: Tom Messenger <kristKILLspamTHEGRID.NET> >Reply-To: pic microcontroller discussion list <.....PICLISTKILLspam.....MITVMA.MIT.EDU> >To: EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU >Subject: Re: [EE]: Noise problem with schmidt trigger >Date: Sun, 11 May 2003 18:00:47 -0700 > >It sounds like you have a fairly high input impedance to your schmitt >trigger making it sensitive to electrical noise. If your circuit does not >require high input impedance, try lowering it. > >What is connected to the input of the schmitt trigger? > > >At 12:48 AM 5/12/03 +0000, you wrote: > >I have a schmidt trigger connected to my microcontroller counting the >number > >of pulses coming from the schmidt trigger. I notice that whenever any >power > >supply is turned on (DC power supply unit, any step down transformer), >the > >counter value jumps unpredictably. When I remove the input to the schmidt > >trigger(microcontroller to schmidt trigger wire is still there), >everything > >is fine. I replace the input to the schmidt trigger with just a long wire > >and the problem appears again. > > > >It seems to me that the schmidt trigger has very low threshold value, to >the > >extend that it interprets these noise as a signal. Is there anyway I can > >solve this problem? I thought of a rather stupid solution as to wrap the > >input wire to the schmidt wire with aluminium foil. Will it work? > > > >Thanks > >Mark > > > >-- >http://www.piclist.com hint: To leave the PICList >piclist-unsubscribe-requestspam_OUTmitvma.mit.edu _________________________________________________________________ Protect your PC - get McAfee.com VirusScan Online http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963 -- http://www.piclist.com hint: To leave the PICList @spam@piclist-unsubscribe-requestKILLspammitvma.mit.edu>

I wonder if a Schottky diode would help? -marc On 5/11/03 9:37 PM, "Lim KK" <KILLspammark_limkkKILLspamHOTMAIL.COM> wrote: {Quote hidden}> Thanks for your reply. > The input to my schmitt trigger is actually pulses coming from an optical > encoder. 2 pulses of different phases are sent to my microcontroller via two > schmitt trigger to decode the position of the motor. My microcontroller is > configure as an event counter to count these pulses. I tried so many > techniques but fail to find a solution to this problem. Whenever any > equipment with transformer is switched on nearby, the counter jumps wildly. > > Being a rather lousy student myself, can you explain how can I lower the > high input impedance to my schmitt trigger? The wire carrying the pulses > from the optical encoder to the schmitt trigger is about 2meters long. > > Thanks alot! > Mark > > >> From: Tom Messenger <RemoveMEkristTakeThisOuTTHEGRID.NET> >> Reply-To: pic microcontroller discussion list <spamBeGonePICLISTspamBeGoneMITVMA.MIT.EDU> >> To: TakeThisOuTPICLISTEraseMEspam_OUTMITVMA.MIT.EDU >> Subject: Re: [EE]: Noise problem with schmidt trigger >> Date: Sun, 11 May 2003 18:00:47 -0700 >> >> It sounds like you have a fairly high input impedance to your schmitt >> trigger making it sensitive to electrical noise. If your circuit does not >> require high input impedance, try lowering it. >> >> What is connected to the input of the schmitt trigger? >> >> >> At 12:48 AM 5/12/03 +0000, you wrote: >>> I have a schmidt trigger connected to my microcontroller counting the >> number >>> of pulses coming from the schmidt trigger. I notice that whenever any >> power >>> supply is turned on (DC power supply unit, any step down transformer), >> the >>> counter value jumps unpredictably. When I remove the input to the schmidt >>> trigger(microcontroller to schmidt trigger wire is still there), >> everything >>> is fine. I replace the input to the schmidt trigger with just a long wire >>> and the problem appears again. >>> >>> It seems to me that the schmidt trigger has very low threshold value, to >> the >>> extend that it interprets these noise as a signal. Is there anyway I can >>> solve this problem? I thought of a rather stupid solution as to wrap the >>> input wire to the schmidt wire with aluminium foil. Will it work? >>> >>> Thanks >>> Mark >>> >> >> -- >> http://www.piclist.com hint: To leave the PICList >> RemoveMEpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu > > _________________________________________________________________ > Protect your PC - get McAfee.com VirusScan Online > http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963 > > -- > http://www.piclist.com hint: To leave the PICList > piclist-unsubscribe-requestEraseME.....mitvma.mit.edu > -------------------------------------------------- Marc Nicholas Geekythings Inc. C/416.543.4896 UNIX, Database, Security and Networking Consulting -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestmitvma.mit.edu>

At 01:37 AM 5/12/03 +0000, you wrote: >Thanks for your reply. >The input to my schmitt trigger is actually pulses coming from an optical >encoder. 2 pulses of different phases are sent to my microcontroller via two >schmitt trigger to decode the position of the motor. My microcontroller is >configure as an event counter to count these pulses. I tried so many >techniques but fail to find a solution to this problem. Whenever any >equipment with transformer is switched on nearby, the counter jumps wildly. > >Being a rather lousy student myself, can you explain how can I lower the >high input impedance to my schmitt trigger? The wire carrying the pulses >from the optical encoder to the schmitt trigger is about 2meters long. > >Thanks alot! >Mark It's difficult to know the best approach without seeing your circuit. Perhaps if you can make a small gif of it, people on the list can suggest better solutions... You also need to verify how the electrical interference enters your circuit. If possible, try running it completely isolated from AC power - use batteries or whatever. See if this works. It may be coming in the opto input to the schmitt trigger or somewhere else. You will have to become adept at guessing where the trouble is and trying to verify your guesses! It is difficult for beginners but after doing so, you will learn a LOT! Good luck! Tom M. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

"The importance of a properly grounded system cannot be overemphasized." - from " OIT Ground Wiring and Electrical Noise Reduction" Another not-so-bad resource on grounding "ELECTRICAL GROUNDING ARCHITECTURE FOR UNMANNED SPACECRAFT" (NASA-HDBK-4001) Or "RELIABILITY PRACTICES ELECTRICAL GROUNDING PRACTICES FOR AEROSPACE HARDWARE" Good links: users.pandora.be/educypedia/electronics/generalelectronicsmis.htm (Grounding and shielding techniques) Good Luck. Mike. > >>> I have a schmidt trigger connected to my microcontroller > >>> counting the number of pulses coming from the schmidt > >>> trigger. I notice that whenever any power supply is > >>> turned on (DC power supply unit, any step down > >>> transformer), the counter value jumps unpredictably. > >>> When I remove the input to the Schmidt trigger > >>> (microcontroller to schmidt trigger wire is still there), > >>> everything is fine. I replace the input to the schmidt > >>> trigger with just a long wire and the problem appears again. ... -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

yup, I tried to pull it up, but the problem persist. The output of the encoder is pulses (0V to 5V). I think the encoder circuit producing the pulses are fine. When I replace the input of the schmitt trigger with a long wire(1m), the problem appears. mark {Quote hidden}>From: Jan-erik Svderholm (QAC) ><RemoveMEJan-erik.SoderholmEraseMEEraseMEPAC.ERICSSON.SE> >Reply-To: pic microcontroller discussion list <RemoveMEPICLISTspam_OUTKILLspamMITVMA.MIT.EDU> >To: RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU >Subject: Re: [EE]: Noise problem with schmidt trigger >Date: Mon, 12 May 2003 09:10:35 +0200 > >Pull up or pull down resistors on the input to >the schmitt trigger ? What is the output from the >encoder ? Just a open or closed switch ? > >Jan-Erik. > > >Lim KK wrote: > >The input to my schmitt trigger is actually pulses > >coming from an optical encoder. > >-- >http://www.piclist.com hint: PICList Posts must start with ONE topic: >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads _________________________________________________________________ STOP MORE SPAM with the new MSN 8 and get 2 months FREE* http://join.msn.com/?page=features/junkmail -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

oh, the long wire is connected to nothing. It's around < 1m. No, there's no "not-so-long-wire". I'm trying to find out how long does the wire need to be in order to cause problem. mark {Quote hidden}>From: Jan-erik Svderholm (QAC) ><EraseMEJan-erik.SoderholmspamspamBeGonePAC.ERICSSON.SE> >Reply-To: pic microcontroller discussion list <RemoveMEPICLISTKILLspamMITVMA.MIT.EDU> >To: PICLISTSTOPspamspam_OUTMITVMA.MIT.EDU >Subject: Re: [EE]: Noise problem with schmidt trigger >Date: Tue, 13 May 2003 13:01:40 +0200 > >And the long wire replaces what exactly ? >What's in the other end of the "long wire" ? >How long is the "not-so-long-wire" ? >Jan-Erik. > > >{Original Message removed}

But when connected to my pulse encoder using a 5m wire + tying the input of the schmitt trigger to a +5V via a resistor, the problem persist. The wire itself is already shielded with the exception of the exposed end (approx 3cm). I'm suprise that such a small transformer can cause these problems. {Quote hidden}>From: Jan-erik Svderholm (QAC) ><spamBeGoneJan-erik.SoderholmSTOPspamEraseMEPAC.ERICSSON.SE> >Reply-To: pic microcontroller discussion list <KILLspamPICLISTspamBeGoneMITVMA.MIT.EDU> >To: EraseMEPICLISTEraseMEMITVMA.MIT.EDU >Subject: Re: [EE]: Noise problem with schmidt trigger >Date: Tue, 13 May 2003 14:12:39 +0200 > >Well, out in the woods, you could probably have a >fairly long wire, in a noisy workshop a much >shorter wire. Of course a long un-terminated >wire will cause this kind of problems. You >have just connected an antenna to your input... > >Jan-Erik. > >Lim KK wrote: > >oh, the long wire is connected to nothing. It's around < 1m. No, there's >no > >"not-so-long-wire". I'm trying to find out how long does the wire need to >be > >in order to cause problem. > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics _________________________________________________________________ STOP MORE SPAM with the new MSN 8 and get 2 months FREE* http://join.msn.com/?page=features/junkmail -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Thanks, I tried that, but everything happen so fast, my uni antique o-scope cannot capture anything. I simulate the noise by flicking the switch of a AC-DC power supply. But I'm sure something came out of the schmitt trigger cos the micrcontroller counter changes. {Quote hidden}>From: Jan-erik Svderholm (QAC) ><@spam@Jan-erik.Soderholm@spam@spam_OUTPAC.ERICSSON.SE> >Reply-To: pic microcontroller discussion list <spamBeGonePICLISTKILLspamMITVMA.MIT.EDU> >To: .....PICLISTspam_OUTMITVMA.MIT.EDU >Subject: Re: [EE]: Noise problem with schmidt trigger >Date: Tue, 13 May 2003 14:25:44 +0200 > >I'd check the signal quality with a o-scope... >Jan-Erik. > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics _________________________________________________________________ The new MSN 8: smart spam protection and 2 months FREE* http://join.msn.com/?page=features/junkmail -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

How exactly do you have the wire shielded? Is it coax, or twisted pair, or shielded untwisted, or what? You may be able to fix it simply by using a twisted pair wire. I had a project go south when I ran 8-strand untwisted cable, but replacing it with CAT-5 ethernet cable fixed it right up. Without the CAT-5, I was getting peak noise of two volts on the end of the wire, and that was with it running through a grounded metal conduit! Mike H. {Quote hidden}>From: Lim KK <TakeThisOuTmark_limkk.....TakeThisOuTHOTMAIL.COM> >Reply-To: pic microcontroller discussion list <TakeThisOuTPICLISTKILLspamspamMITVMA.MIT.EDU> >To: .....PICLISTRemoveMEMITVMA.MIT.EDU >Subject: Re: [EE]: Noise problem with schmidt trigger >Date: Tue, 13 May 2003 12:34:43 +0000 > >Thanks, I tried that, but everything happen so fast, my uni antique o-scope >cannot capture anything. I simulate the noise by flicking the switch of a >AC-DC power supply. But I'm sure something came out of the schmitt trigger >cos the micrcontroller counter changes. > > >>From: Jan-erik Svderholm (QAC) >><RemoveMEJan-erik.SoderholmspamBeGonePAC.ERICSSON.SE> >>Reply-To: pic microcontroller discussion list <spamBeGonePICLIST@spam@spam_OUTMITVMA.MIT.EDU> >>To: TakeThisOuTPICLISTspamMITVMA.MIT.EDU >>Subject: Re: [EE]: Noise problem with schmidt trigger >>Date: Tue, 13 May 2003 14:25:44 +0200 >> >>I'd check the signal quality with a o-scope... >>Jan-Erik. >> >>-- >>http://www.piclist.com hint: The list server can filter out subtopics >>(like ads or off topics) for you. See http://www.piclist.com/#topics > >_________________________________________________________________ >The new MSN 8: smart spam protection and 2 months FREE* >http://join.msn.com/?page=features/junkmail > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics _________________________________________________________________ The new MSN 8: advanced junk mail protection and 2 months FREE* http://join.msn.com/?page=features/junkmail -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics