The hall-effect sensors need about 5-10mA. Depending on the display, that may be just about as much as the rest of the computer. A reed switch with a 10K pullup would certainly be less, though.
Mark Borgerson
And don't forget the mechanism to release the brakes on lockup. It consists of a coil generating a few uAmp at several kV, applied to the appropriate brake handle.
--
Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
Available for consulting/temporary embedded and systems.
USE worldnet address!
Yes it does.
According to the reed switch data sheets I've seen they do have hysteresis: the field strength required to close an open switch is higher than the field strength at which a closed switch opens.
True. Though that's easily ignored by a few lines of code (assuming it's being interfaced to a uC).
If the previous guess of several mA for a hall effect sensor is true, that a lot of current. I don't know about other bicycle computers, but a button battery lasts for years in mine (well, I don't ride a lot so that's not much of a datapoint).
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Grant Edwards grante Yow! I KAISER ROLL?! What
at good is a Kaiser Roll
visi.com without a little COLE SLAW
on the SIDE?
Go for magnet + reed switch. I have two 1-button Schwinn cyclometers that cost me US$9.00+ apiece. I use one of them as-is, for its intended purpose; I use the sensor+cable+socket of the other one as the input signal to a bicycle wheel rev. time logger which I built with a PIC and some EEPROMs. Both work very, very well.
By the way, KISS is very good but simple _and_ cheap is even better. (My own opinion; your mileage may vary. Void where prohibited; should not be used by women who are nursing or pregnant or who may become pregnant; common symptoms are usually mild and include vomiting, headache, cough, dizziness, stuffy head ...)
Richard Sloan wrote:
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