From: Dave H. <dhy...@gm...> - 2005-10-13 18:05:43
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I got an email from Liz though the wiki. Unfortunately, I got an error saying ecegal (her wiki id) can't receive messages, and no email was provided. So I'm posting my response to the list in the hopes that she'll see it. Hi Liz, What's the max RPM that you need to measure? I'll guess that the bike tire is about 2 ft in diam, which is a circumference of about 6 ft. Max speed is probably around 30 mph =3D 158,400 ft/hr =3D 2640 ft/min =3D 440 RPM. By putting some conditioning/filtering on the reed switch (to get rid of switch bounce) you should be able to do it by using the interrupt feature of the GPIO lines (having the GPIO lines generate an interrupt whenever a change occurs). I'd HIGHLY recommend using a hall effect sensor rather than a reed switch. The reed switch will have lots of bounce which may make decoding the signal much more difficult. You really need to take your magent/reed switch put it on a bike and put it on an oscilliscope and look at the signal. If it's a nice clean signal, then you'll be fine. If it has lots of spikes, then you won't. So before you even get to hooking it up to anything, you need to be able to generate a nice clean pulse for every revolution of the wheel. Dave Hylands >Hi, > >I wanted to build a tachometer using a gumstix product and bumped into your page that details a robostix tachometer. > >My project entails obtaining revs/min of a rotating bike wheel and will be using a magnetic reed sensor/switch. > >Is it possible to obtain the RPM data using the gumstix 200xm with an additional waysmall RS232 platform? > >Any comments or suggestions will be highly appreciated. > >Thank you for your time, > >Liz -- Dave Hylands Vancouver, BC, Canada http://www.DaveHylands.com/ |
From: Keith O. <kso...@gm...> - 2005-10-13 21:08:15
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It's kind of ironic - two problems in the same day that can be solved with the same technology. (i.e. using a opto-interrupter module (like from a ball mouse)). She could mount a comb-disk on the hub and it would be immune to bounce, though she would want to protect it from getting dirt/mud/etc. in it. Check my previous post for more details. Dave Hylands wrote: >I got an email from Liz though the wiki. Unfortunately, I got an error >saying ecegal (her wiki id) can't receive messages, and no email was >provided. So I'm posting my response to the list in the hopes that >she'll see it. > >Hi Liz, > >What's the max RPM that you need to measure? > >I'll guess that the bike tire is about 2 ft in diam, which is a >circumference of about 6 ft. Max speed is probably around 30 mph = >158,400 ft/hr = 2640 ft/min = 440 RPM. > >By putting some conditioning/filtering on the reed switch (to get rid >of switch bounce) you should be able to do it by using the interrupt >feature of the GPIO lines (having the GPIO lines generate an interrupt >whenever a change occurs). > >I'd HIGHLY recommend using a hall effect sensor rather than a reed >switch. The reed switch will have lots of bounce which may make >decoding the signal much more difficult. > >You really need to take your magent/reed switch put it on a bike and >put it on an oscilliscope and look at the signal. If it's a nice clean >signal, then you'll be fine. If it has lots of spikes, then you won't. >So before you even get to hooking it up to anything, you need to be >able to generate a nice clean pulse for every revolution of the wheel. > >Dave Hylands > > >>Hi, >> >>I wanted to build a tachometer using a gumstix product and bumped >> >into your page that details a robostix tachometer. > >>My project entails obtaining revs/min of a rotating bike wheel and >> >will be using a magnetic reed sensor/switch. > >>Is it possible to obtain the RPM data using the gumstix 200xm with an >> >additional waysmall RS232 platform? > >>Any comments or suggestions will be highly appreciated. >> >>Thank you for your time, >> >>Liz >> >-- >Dave Hylands >Vancouver, BC, Canada >http://www.DaveHylands.com/ > -- Keith Olson K-Soft Consulting oth...@pm... hco...@fm... zou...@hp... rdi...@sb... pen...@ls... ela...@ea... gin...@mw... fcu...@np... fwh...@hs... rra...@ga... |