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previous: RobB I donít know what the frequency lim... -- 10/2/2004 11:34 AM view thread

Re: pickup winding

10/2/2004 3:34 PM
Joe Gwinn
Re: pickup winding
Both reed switches and small microswitches are fast enough, but do need to be debounced.  
 
At 720 RPM, which is 12 revolutions per second, each revolution takes 83 milliseconds. Reed switches respond in a few milliseconds, while microswitches take a few tens of milliseconds.  
 
The contacts of mechanical switches physically bounce on closing, and an electronic counter will count each bounce as an event, yielding a "turns count" a factor too large. Mechanical counters are too slow to follow the bounce, and so give the correct answer.  
 
Some electronic counters have built-in debounce circuitry. If not, one must provide it. All that's needed is a schmitt-trigger input CMOS logic IC, a tantalium capacitor, and a resistor or two.  
 
Electronic switches, like optical interrupters, have no bounce, but still can jitter enough to cause false counts, so a debouncer is still useful. Hall-effect magnetic switches usually have the debouncing (hysteresis) built in.