Have you tried a TVS diode across the relay coil? TVS diodes are sometimes effective across VCC to GND in addition to the other if the system is in a high noise environment. ----- Original Message ----- From: "Cedric Chang" To: "Microcontroller discussion list - Public." Sent: Monday, March 24, 2008 11:42 PM Subject: Re: [EE] question on a motor noise problem 2: motor > > >> On Mar 24, 2008, at 5:56 PM, gardenyu wrote: >> >> Thanks a lot for your kind reply. >> >> I would look at D2 tomorrow, if this is really an issue, do you >> have any suggestion on cutting this surge off? RV2 is supposed to >> be a surge protector, maybe it's not strong enough. >> >> It's some new version that I have, for some reason the designer >> didn't like the snubber, >> >> the relay is certainly a problem, I noticed before that when it's >> turned off and not yet turned on, the voltage can rise quite high >> that causes the relay to click back and forth for times. Do you >> have any suggestion on related problem? Thank you so much. >> >> >>> From: cc@nope9.com> Subject: Re: [EE] question on a motor noise >>> problem 2: motor> Date: Mon, 24 Mar 2008 15:49:53 -0600> To: >>> piclist@mit.edu> > I would resume that circuitry not shown ( some >>> form of logic ) gets > a surge of voltage applied to it and that >>> it enters some unexpected > state. My recommendation is to measure >>> the voltage at pin 2 of D2. > If you are getting drive voltage at >>> pin 2 after the "stop" is pushed, > then your logic is getting >>> hammered by a voltage spike.> > Are Q4 and Q? ( the Q below Q4 ) >>> acting as an active motor brake ? > The circuitry shown does not >>> seem to offer any snubbing of the > voltage spike you would get >>> from the motor. The relay is going to > allow the motor to be >>> disconnected for several milliseconds, > certainly long enough to >>> allow voltage spiking to occur. I am > assuming the relay is a >>> "break before make" variety, otherwise I > don't see how the relay >>> contacts would survive.> > This design seems a bit strange to me. >>> I await the commen >> ts of other > PLs. The fact that R25 is missing renders C20 as >> useless.> > cc> -- > http://www.piclist.com PIC/SX FAQ & list >> archive> View/change your membership options at> http:// >> mailman.mit.edu/mailman/listinfo/piclist >> > > Without seeing the rest of your circuit, i cannot suggest a "best > solution". I can suggest that you put a voltage snubber on the DRIVE > + line. The maximum voltage you apply to the DRIVE+ line dictates > the voltage rating of the parts you use for the voltage snubber. Try > first putting an MOV ( metal oxide varistor ) across DRIVE+ to > ground. Multiply the maximum voltage for DRIVE+ by 1.1 and select an > MOV that has that voltage rating. Without knowing how much current > your motor draws and it's inductance, I would say start with an MOV > that absorbs about 5 Joules. I also don't know where you buy parts, > so I cannot suggest a source for the MOV. > > cc > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist