Conference noted::bicycle

1203.0. "Avocet mod 30 Cyclocomputer tech note" by GUESS::YERAZUNIS (Artificial Intelligence, Advanced Systems and Tools Group) Tue Jun 13 1989 12:28

    I captured the following Tech Note from Avocet from the Usenet:
    	-Bill
     ------------------------------
       
    
Path: shlump.dec.com!decwrl!hplabs!hp-ses!hpcuhb!hpcllla!hpclisp!chip
From: [email protected] (Chip Chapin)
Newsgroups: rec.bicycles
Subject: Avocet Tech Note (cyclometers)
Message-ID: <[email protected]>
Date: 1 Jun 89 16:32:28 GMT
Organization: Hewlett-Packard Calif. Language Lab
Lines: 91
 
A friend who deals a lot with the folks at Avocet, and who occasionally
hears from the notes world, sent me this official (I think) bit of news
from Avocet regarding their cyclometers, in hopes of displacing some
speculations with facts.
 
DISCLAIMER: I am not associated with Avocet in any way, and am simply
posting this for the benefit of the net.
 
Chip Chapin -- HP Computer Language Lab, Cupertino CA
-------------------------------------------------------------
 
 
NEWSNOTE from AVOCET
 
Copies of recent rec.bicycle postings forwarded to Avocet
suggest that a technical newsnote might be useful.  Bicycle
computers or cyclometers, as the Avocet units are called, have
numerous design considerations that must be addressed.
Mechanically there is size, mounting simplicity, functional
shape and controls, visibility, durability, water resistance,
and a lot of other fine points.  Electrically there are
primarily two concerns, other than an appropriate function
program, and these are: accurate pickup, and power consumption.
 
In the program department Avocet differs from the others in
that it displays only speed, distance and time.  It uses a
custom CMOS chip that relies entirely on counters and does no
arithmetic.  This approach was chosen because it was believed
that these were the essential functions and that the most
reliable unit could be made using such a device.
 
 
 1.  The AVOCET cyclometer, unlike others, uses an inductive
     pickup that generates an alternating current signal.  An
     elastomeric magnet ring with 20 magnetic poles (ten north
     and ten south) is attached to the hub.  The poles can be
     detected by moving a piece of iron around on the face of
     the magnet.  A pickup-to-magnet spacing of 1 to 2 mm can
     detect speeds as low as 2 mph.
 
 2.  Speedometers that do not use a continuous magnetic ring,
     (all others) use a reed switch as a detector.  Because a
     reed switch does not generate any power, a sense current
     furnished by the battery is needed.  If the wheel stops
     when the magnet is opposite the reed switch, the sense
     current can drain the battery.  Reed switch cyclometers
     with a single magnet must average over four seconds in
     order to achieve 2 mph smoothly and consistently.  One
     wheel revolution per two seconds equals about 2.5 mph.
 
 3.  Reed switches have two parallel pin like iron rods that
     are closely spaced and have contacts at their free ends.
     In the presence of a magnetic field these reeds attract
     each other and close the contacts.  These contacts wear
     with repeated closure and can become unreliable.  More
     important is that reed switches can make contact from
     mechanical shock and are generally not used in vibrating
     applications such as on a bicycle.  For example, one false
     count in a revolution can double your speed.
 
 4.  The AVOCET circuit does not use an arithmetic unit so it
     does not average nor does it perform any conversions.
     With every flux reversal (20 per revolution) the
     calibration number is added to a register.  At the end of
     a clocking cycle the sum of these counts is displayed as
     speed and the cumulative count as distance.  The accuracy
     is derived from the resolution of the calibration number.
 
 5.  Erratic readings on Avocet cyclometers may arise from
     intermittent pickup contact.  Information can only be lost
     and speed or distance cannot exceed the actual traveled.
     Not obvious to the user, the wires to the pickup are
     plugged into the coil at the fork end.  Although they may
     look like permanent connections these contacts must be
     fully engaged and secured by using a cable tie directly
     above the pickup to secure the cable to the fork as shown
     in the instructions.  Otherwise a wheel change or off road
     riding through weeds can loosen these wires.
 
 6.  The Avocet cyclometer 30 has three primary and three
     background functions.  Speed, trip distance and elapsed
     time are the primary functions while maximum speed, total
     distance and time of day reside in the background.  Each
     function except total distance can be re-set individually.
     The cyclometer 30 is interchangeable with the 20 and uses
     the same battery.  The elimination of screws in the housing
     has made the Cyclometer 30 waterproof.  New colors are: lime
     green, day-glo pink and celest.
        
Avocet hopes this will clarify a number of points that have
come up in recent postings.
    

    Heres my assessment of the Avocet Mod 30 compared to a Cateye Solar
    
    	The mounting is easier and performs better, i.e., the little mod 30 ring
    magnet mearly clips to the wheel unlike the cateye screw it onto the spokes
    and adjust it unit.
    
    	The tie down for the sending unit on the mod 30 is also superior as
    is the nice neat little size (and color)
    
    	Where the mod 30 really blows though is in the timing.  Unlike the
    cateye the mod 30's stop watch only records minutes and seconds. 
    Besides TT riders, who can use this feature???  The clock is neat so
    if you remember what time you started you can calc your own E.T., but
    the cateye lets you stop and start the timer to account for such 
    things as brakes if your just trying to record time actually on the
    bike.
    
    	The other feature that I miss most is Average Speed for the ride.
    If you use the start/stop button on the cateye mentioned above you
    can get a fairly good reading of how hard your ride was in terms
    of average speed achieved. (I know you can calc this with the mod 30
    but I'm talking about ease of use.)
    
    	Overall I really like the Mod 30 but will only put one on my
    short ride bikes.  It's not what I'd call a *touring* cyclometer.
    
    							Jerry
    BTW - Another thing I like about the mod 30 is that it appears
    to be made in the USofA.

    I rarely have much trouble mentally keeping track of how many
    hours I've been on the bike.
    
    In fact, my butt keeps track of it for me.  The diameter of the
    rash (in cm) divided by 1.78 is the time in-saddle.  :-)
    
    	-Bill (with a blue model 30, and a recurrent prescription for
    		Lotrimin ointment  :-(  )

    I have not used the model 30; model 20's at $25 on disposal sale
    sufficed.  But the timer function (if that is what .0 refers to)
    on the 20 shifts from minutes:seconds to hour:minutes when you pass
    one hour.  It's pretty obvious when it happens.  Have you used
    it on your bicycle for more than an hour?

    re. -1
    
    	That was my complaint.  On rides lasting three to four hours
    or more, you tend to loose tract of the exact time that you
    started and the model 30 just rolls over after 60 minutes and
    starts counting minutes again.  If they had it right on the
    model 20 they sure blew it when they went to the model 30 :-(
    
    						Jerry