I wonder if a Schottky diode would help? -marc On 5/11/03 9:37 PM, "Lim KK" 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 > > >> From: Tom Messenger >> Reply-To: pic microcontroller discussion list >> To: PICLIST@MITVMA.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 >> mailto:piclist-unsubscribe-request@mitvma.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 > mailto:piclist-unsubscribe-request@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 mailto:piclist-unsubscribe-request@mitvma.mit.edu