Post by thread:[PIC] Is there a need for HALL debouncing

> Hi there, > > Is there a need for a piece of debouncing check on slow moving HALL > sensors > connected to a MCU? > > Harry I don't think so, but the input should be a Schmitt input to reject electrical noise. The output of the Hall effect sensor will directly follow the magnetic field and not suffer from bounce like mechanical contacts. Harold -- FCC Rules Updated Daily at http://www.hallikainen.com - Advertising opportunities available!

Course not, its a solid state switch, nothing bouncing like a mechanical contact. On the other hand, you might consider multiple polls to ensure the sensor is active and your not just reading noise on the line (depending on how you have it designed). --- On Thu, 8/14/08, Harry H. Arends <spam_OUTh.arendsTakeThisOuThome.nl> wrote: {Quote hidden}> From: Harry H. Arends <.....h.arendsKILLspam@spam@home.nl> > Subject: [PIC] Is there a need for HALL debouncing > To: "'Microcontroller discussion list - Public.'" <piclistKILLspammit.edu> > Date: Thursday, August 14, 2008, 5:46 AM > Hi there, > > Is there a need for a piece of debouncing check on slow > moving HALL sensors > connected to a MCU? > > Harry > --

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Harry H. Arends wrote: > Hi there, > > Is there a need for a piece of debouncing check on slow moving HALL sensors > connected to a MCU? > > Harry Depends how slow--if the output swings _really_ slow you might have some problems if the device is rotated through the Earth's field or a piece of machinery is moved past it. It would be best to put it through a Schmitt trigger to be safe. - -- Brendan Gillatt | GPG Key: 0xBF6A0D94 brendan {a} brendangillatt (dot) co (dot) uk http://www.brendangillatt.co.uk -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (MingW32) iD8DBQFIpDA7uv4tpb9qDZQRAiG4AKCa9U3lDmLWF8uKD0/Iz4+84NCaZACgqhNV yuxS83QaeiCfYh5hlfKUowM= =t866 -----END PGP SIGNATURE-----

Quoting "Harry H. Arends" <.....h.arendsKILLspam.....home.nl>: > Hi there, > > Is there a need for a piece of debouncing check on slow moving HALL sensors > connected to a MCU? > > Harry Probably not. Read the data sheet. If there is built-in hysteresis, then no (unless you want to reject noise glitches, which is not really debouncing). For example, the Panasonic DN6849 has minimum 7 (typical 10) mT of hysteresis. If there is no built-in hysteresis then mechanical vibration or perhaps power supply noise could cause a sort of 'chattering'. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" EraseMEs...spam_OUTTakeThisOuTinterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com

Harry H. Arends wrote: > Is there a need for a piece of debouncing check on slow moving HALL > sensors connected to a MCU? Any signal can have noise. It would be a good idea to use hysteresis at least a bit greater than the noise. ******************************************************************** Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products (978) 742-9014. Gold level PIC consultants since 2000.

> Harry H. Arends wrote: >> Is there a need for a piece of debouncing check on slow >> moving HALL >> sensors connected to a MCU? Olin escrit > Any signal can have noise. It would be a good idea to use > hysteresis at > least a bit greater than the noise. What he says. While in many cases the hysteresis which is often included in Hall sensors will be enough, the result will vary with application. Depending on how the magnetic field variation is produced you may get "noise" or may not. If you are monitoring a rotating shaft (or similar object) then inertia/momentum/natural cussedness will mean that you probably only see 'vibration' bucking the trend and most Hall sensors will probably work OK. If you are monitoring something like a door / safety interlock etc then you may be more at risk. But even with a rotating shaft "vibration" may be due to eg bearings beginning to fail or an out of balance load, so what works this week as an RPM monitor may work next month as a bearing failure or out of balance load detector. Also, as Olin suggests, noise may be injected electrically in some manner - circuit impedance, inductive pickup and signal strength (and more) will help affect how great the resultant noise is. "Relay turning off / inductive kick" transients, which love to ride in on all sorts of other signals may find a magnetically coupled path for this one. Looking at the signal on a scope and comparing the observed variations with the sensor's hysteresis spec (or measured hysteresis characteristic in the absence of a spec) will give you a rough feel for what is or isn't required. Failure in service in equipment 4000 km away will give you a finer feel :-). Russell