I snagged the wire on my Cateye Mity 8 computer on the rack the other day and broke it mid wire. I'm going to fix it by splicing them back together. I'm worried about effects of getting the wires crossed. I'm going to take some care not to cross them, but if I do, will it cause problems? What readings should I get from it with a multi-meter?

  • It's worth noting a new one, with zip ties and everything, is around $10: google.com/…. – super Jul 8 '15 at 19:24
  • Yeah, but cutting off a few inches of cable around the break point and splicing the cable together is well under 10 dollars. – Batman Jul 8 '15 at 19:48
  • I would guess that the two wires have different colored insulation. – Carl Jul 8 '15 at 20:35
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    Look very carefully at the wire. It's hardly ever the case that there is not some identifying mark (often a thin rib on the jacket) marking one conductor vs the other. Or one conductor may be silver, the other copper. Or, as Carl suggests, they may have different color inner insulators. – Daniel R Hicks Jul 9 '15 at 0:38
  • I did order a replacement and it was over $15 form Niagara. However I was able to splice the broken one without determining which wire was what. I still count tell the difference. I could have counted strands but there was only five in each side. – BPugh Jul 10 '15 at 3:02

There are a few ways you can do the magnet sensing:

  1. Reed switch (a switch which physically closes with a magnetic field). If you swap the two wires, the sensor will work fine (i.e. it doesn't matter). You can test for this using the continuity tester mode of your multimeter (you'll have continuity if the magnet is near the sensor, and open circuit with the magnet far away).

  2. Hall effect sensor (Generally, there are 3 wires on here: Vdd, ground and the output of the sensor). There are 3!=6 ways you can wire it (so 5 ways to mess it up). Most likely, you won't get a reading from the sensor until you get it right if you don't hook it up correctly. As noted by Chris H, if you have a Hall effect sensor, chances are the wires will be color coded so you'll figure out Vdd and ground, and the remainder is output. Your multimeter won't really help you here.

  3. An inductor (basically, a coil of wire). If you swap the two wires, the sensor would work fine (it'd be equivalent to moving the sensor to the other side of the bike, i.e. it doesn't matter). Your multimeter will show continuity always, but if you have a LCR meter, you can check the inductance. If you measure resistance, you should see a few ohms.

So, basically, if you have 2 wires, chances are you can swap them without worrying and the thing should work. If you have 3, maybe you'll have to disassemble the sensor, figure out which sensor is in there and then look up the pinout (or guess based on color coding of the wires).

There are a few more types of magnetic switches, but they're unlikely to occur in this application.

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    You'd have to be really unlucky to have a hall sensor and no colour coding. Anyway zooming right in to the manual for that model shows what looks like figure-of-8 cable, i.e. probably 2 wires (though it could still be like headphone wire). – Chris H Jul 8 '15 at 15:52
  • It's happened before on other products, esp. now electronics are considered disposable. – Batman Jul 8 '15 at 15:59
  • that's true, but it does make assembly harder so seems to be rare. – Chris H Jul 8 '15 at 16:01
  • @ChrisH It is a 2 wire setup. However, there is no markings on the wire to suggest which goes to which, so I have to stare at the break for a while to figure it out. I can't imagine this being a reed switch though due to the shear number of times it would get activated, but I have noticed a tick when near it. Either way, I have a go at it tonight. – BPugh Jul 8 '15 at 17:42
  • Even a cheap reed switch would work for tens of thousands of miles (esp. in low voltage+current applications like this one) -- you're much more likely to destroy the cable or something else before the switch goes (and it is known Garmin among others use reed switches in some of their models). If you hear a tick near it, it is a reed switch. – Batman Jul 8 '15 at 17:56

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