Originally Posted by
JBHoren
Cateye bicycle computers all work on the spoke-mounted-magnet passing a fork-mounted sensor. When programming the unit, you can enter two sets of tire circumference, and switch between them. They have wired and wireless models, providing current speed, min/max speed, total distance, and two "trip"-distance odometers. Available at all price points. I own the Cateye "Strada" wireless model, and couldn't be happier (unless I had a spare $55 for the much larger screen of their "Padrone" model).
I bought a CatEye Velo 7, largely based on Amazon's reviews. It doesn't have the option to enter two circumferences, but it's not expensive, and a 2nd head can be used as someone suggested. But it's limited to circumferences between 100cm and 299 cm. I need 76cm, so I'm trying to figure how I can use a 152cm setting, but my brain putzes before solving it.
As my user name suggests, we're a family of dyers. We dye wool yarn. Some of what we sell is put up in 20 yard hanks which will soon be made by wrapping it around a rotating drum whose circumference is 30". A second size partial skein is sold in 100 yard hanks with a circumference of 48". Those are made on a stepped portion of the same drum. The drum is long enough so that I can wind as many as 8 of the smaller ones at a time. The drum will be manually cranked using puleys & a timing belt with a mechanical advantage of 1:4.5, and I'm looking for a device to tell me when I'm done.
Originally Posted by
FBinNY
Unless they changed, sigmasport computers allow you to key in any wheel circumference from 0001mm to 9999mm. So , you could, for example punch in 1000mm, or 1 meter. Then every km would equal 1,000 revolutions, or 0.1km would equal 100revs. I don't know the speed you're considering, but with a round number wheel the speedometer would read in rpms (multiplied)
If you want greater resolution you could enter a wheel of only 100mm, or even 10mm. However you might run into limitations on the speedometer.
Otherwise, (just about) any bicycle computer sensor and magnet could be pulse counter, and you'd need some basic circuitry to read it out.
My bad. I didn't make my requirements very clear. Speed functions aren't really important. I'm looking to measure very short distances. You mention the idea of greater resolution, and I'm wondering if that would help me achieve a meaningful number the display of whatever unit I ultimately decide. I can almost apply what you're saying here, but there's something I'm not getting. My math was never great, and has only gone downhill over the years. How do I go about calculating the figure I need to enter so the display is one that I can interpret at a glance? The metric equivalents (762mm and 1220mm) of the imperial circumference measurements (30" and 48") I'm after is just fine if that's easier.