Robert Bullock wrote: > -----Original Message----- > From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of > Mark Rages > Sent: Sunday, August 16, 2009 12:09 PM > To: Microcontroller discussion list - Public. > Subject: Re: [PIC] Bicycle Speedometer Project > > On Sun, Aug 16, 2009 at 9:44 AM, Robert Bullock wrote: > >> I would not rule out the use of a Hall Effect sensor quite so quickly. >> > > >> ... >> > > >> Researching more, I see that Infineon has one that looks perfect for your >> application. >> It is very low power, (typically 4 uA averaged supply current ) and is >> designed for >> Battery operation from 2.4 to 5.5 volts. >> >> Infineon TLE4913 >> >> Digikey TLE4913INCT-ND $0.92 qty 1 >> >> > > As I mentioned in my message, "low-power" sensors are actually duty > cycled. This one is on for 50 us, then off for 200 ms. It is not > suitable for measuring the period of a bicycle wheel: the spoke magnet > could easily pass by in the 200 ms that the sensor is off. Even if > you find one with a fast enough sampling frequency, it will still > quantize the period to that frequency. So short-term speed resolution > will suck compared to a reed switch. These hall sensors are made to > notice your cell phone or laptop being open, not to actually measure a > period. > > The humble reed switch is best for this application. I'm not sure why > everyone is looking for something else. > > Regards, > Mark > markrages@gmail > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist