Re: Counting Bike Wheel Revs

In article <1je0f19r2vv21hm02pgtghvegmjcuufcr7@xxxxxxx>,
ben_nospam_bradley@xxxxxxxxxxxxxxx says...
> On Tue, 02 Aug 2005 14:11:52 -0000, Grant Edwards <grante@xxxxxxxx>
> wrote:
>
> >On 2005-08-02, Mark Borgerson <mborgerson.at.comcast.net> wrote:
>
> >>> A reed-switch OTOH, is dead simple to interface to. All you
> >>> need is an input port pin (or IRQ pin) and a pullup resistor.
> >>>
> >> True. But does it have the same sensitivity, a built-in schmidt
> >> trigger and other features (about which I know little)?
>
> A reed switch doesn "Schmidtt triggering" naturally, though there
> may be a slight problem with contact bounce, that a Hall effect sensor
> won't have.
>
> >>
> >> Reed switches are about $0.39 qty 1000 in the Jameco catalog,
> >> but you still need to mount it, make sure it is oriented
> >> properly, and protect it from breakage. A 3-Pin SIP Hall
> >> sensor might be worth the extra $0.60.
>
> Don't you also need to mount a Hall effect sensor, make sure it is
> oriented properly, and protect it from breakage? Okay, it's not glass
> like a reed switch, but it still needs to be 'adjusted' in relation to
> the magnet on the wheel, just as does the reed switch.
>
> >I would think that either would work fine.
> >
> >> I've used reed switches, but never on the fork of a bicycle,
> >> where shock and vibration might be an issue. Are those issues
> >> in favor of a Hall sensor?
> >
> >I don't remember bicycle computers ever having any problems
> >with them.
>
> Reed switches also have the advantage of being totally passive and
> not needing power. An integrated-circuit Hall sensor probably takes
> (just a swag, I haven't looked at a data sheet lately) 100 or 1,000
> times as much power as the average electronic bicycle
> speedometer/computer.

The hall-effect sensors need about 5-10mA. Depending on the display,
that may be just about as much as the rest of the computer. A reed
switch with a 10K pullup would certainly be less, though.

Mark Borgerson

.

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