how to build rpm circuit?

[ecegal]

Hi,<p>am new to this forum and would like to build a circuit that measures rpm while pedalling a stationary bike (UBE). I'd like to store the data to a computer and retreive it for future analysis. <p>Ideas I have so far? Am thinking of sticking reflective tape on the bike shaft, using an optical sensor and circuit to detect and measure rpms.<p>Any suggestions or comments will be greatly appreciated. <p>Thanks

[Newz2000]

Howdy! I recently saw this and thought it would be an excellent tool for a biker:
http://veloace.sourceforge.net/<p>Basically, you buy an old palm pilot on e-bay (like the Palm III - see link below) for $10 - 15. Then, you build the small cable described on the link above. It tracks all kinds of interesting details about your bike ride and shows real time stats on the palm pilot (which is now strapped to your handle bars). It also stores it so that it can be periodically downloaded to your computer in spreadsheet/database format and annalyzed.<p>This project doesn't require much work so may not be too fun, but it does look like it has an interesting and useful interface.<p>[ September 12, 2005: Message edited by: Matt Nuzum ]
Here is the link directly to the ebay search page for some good palm pilots. I had to break it up into several lines. The end result should all be on one line before you use it:
listings.ebay.com/_W0QQsocmdZListingItemList?sofocus=pf
&sbrftog=1&catref=C3&socmd=ListingItemList&from=R2
&satitle=&sacat=38331%26catref%3DC6&a14=1759&a10255=10269
&a12=-%2024&a35=-24&a10244=-24&gcs=7&pfid=7&reqtype=2
&pfmode=1&alist=a14%2Ca10255%2Ca12%2Ca35%2Ca10244
&pf_query=&pf=Show+Items&sargn=-1%26saslc%3D2&sadis=200
&fpos=50313&ftrt=1&ftrv=1&sabdlo%20=&sabdhi=&saprclo=
&saprchi=&fsop=1%26fsoo%3D1&coaction=compare&copagenum=1
&coentrypage=search<p>[ September 12, 2005: Message edited by: Matt Nuzum ]</p>

[Externet]

Hello.
Attaching a magnet or a few to the turning part you want to measure, and a stationary coil swept by it, you generate, then rectify and filter, enough amount of electricity to move a D'Arsonval meter.
Miguel

[philba]

both a magnet/hall-effect device or phototransistor/led would work pretty well. I like the idea from veloace of using the RTS line of a serial port. I'm not sure I like the use of flipflops - I would just use a low pass filter with a cutoff frequency of 2X the max rate (noise rejection) then into a schmitt trigger and then the RTS line of the com port.<p>The veloace software should work with it.<p>If you want more detail, just ask.<p>Phil

[sofaspud]

My Vetta bike computer uses a coil attached to the front fork and a small magnet that clamps onto the front wheel spoke. It's been a reliable system, with just a "set it and forget it" input from me. It needed calibration originally for speedometer/odometer readout but an RPM sensor wouldn't even need that.

[ezpcb]

Hi Philba<p>this filter plan may run in trouble, notice that the speed of the bicycle can be various from 5mph to 30mph, how to determin the cut-off freq of the filter?<p>I think a several hundred pf capacator between the GND and input of schmitt triger will work as the noise canceller. Only the very high freq noises needs to be trimmed.<p>A PIC with software counter is the solution I preferred.
<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by philba:
both a magnet/hall-effect device or phototransistor/led would work pretty well. I like the idea from veloace of using the RTS line of a serial port. I'm not sure I like the use of flipflops - I would just use a low pass filter with a cutoff frequency of 2X the max rate (noise rejection) then into a schmitt trigger and then the RTS line of the com port.<p>The veloace software should work with it.<p>If you want more detail, just ask.<p>Phil<hr></blockquote>

[philba]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by ezpcb.com:
Hi Philba<p>this filter plan may run in trouble, notice that the speed of the bicycle can be various from 5mph to 30mph, how to determin the cut-off freq of the filter?<p>I think a several hundred pf capacator between the GND and input of schmitt triger will work as the noise canceller. Only the very high freq noises needs to be trimmed.<p>A PIC with software counter is the solution I preferred.
<hr></blockquote><p>I'm not sure what you mean by trouble. You are suggesting what amounts to a low pass filter. I'd pick the highest RPS - say 15 for arguments sake. That would be 15 hz. Double that for the 3 db cut off point. so a low pass for 30 would be a 4.7 uF cap and a 1K resistor. Actually, the cut off is 33.9 hz with those (standard) components. All the high frequencies would be filtered and the circuit would not have particularly high impedence. If the max RPS was 75, pick a 1 uF cap. The cut off freq formula is f = 1/(2*pi*R*C) C is in Farads - 1 uF = .000001 F. <p>Interestingly, the velo ace sensor (vaif2) uses D flip flops to do a crude form of debouncing (they seem to use mechanical switches!!) and also noise reduction. Basically, I don't think it works very well for either. A low pass and schmitt trigger, as I suggested, would be much more effective and I'd junk the mechanical switch to get rid of bounce.<p>I personally would use a uC for this but the original poster wanted to get it into a computer and didn't indicate electronics sophistication. Since the RTS thing has software that supposedly works - crafting a sensor to mimic that would serve him best.

[jimandy]

Philba: <blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr> A low pass and schmitt trigger, as I suggested, would be much more effective and I'd junk the mechanical switch to get rid of bounce.<hr></blockquote><p>Ah, the venerable schmitt trigger!. At last I don't feel alone in the world.

[ecegal]

Thank you all for your input. These are some good leads to go on

[Robert Reed]

Jimandy
Your not alone! The 74HC Schmidts are wonderful devices and come thru where nothing else can. I use them all the time. Your recent reply suggesting the use of Schmidts was right on the money.