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Roger Harvey05/10/2009 14:14:59
9 forum posts
Hello All,
Back in Issue No.  147, Mike Crossfield wrote an article describing a low cost rev-counter. This used a disk with 60 slots to generate 60 pulses per revolution of the spindle.
Is there an electronic device, or a circuit using such a device, that would amplify/multiply the pulses generated by one similar opto switch once per revolution by 60 times. i.e one pulse per revolution increased to 60.
Regards
Wychwar
 
Les Jones 105/10/2009 18:37:31
2292 forum posts
159 photos
Hi Wychwar,
                        I have put a design for a four digit tachometer that uses one pulse per revolution on the "Yahoo X_Series _Mills forum" in the file section.
It works by measuring the time  of one or more revolutions and calculating the speed from that. At slow very slow speeds it only times one revolution. (So the display is updated at a reasonable rate.) At higher speeds it times a number of revolutions to average out the speed over about a one second period.
I hope this will meet your reqirements.
Les.
David Blunn16/10/2009 10:51:12
21 forum posts
Hi,
you could try a Phased Lock Loop (PLL) circuit. Look up (google) some application notes for CD4046 or HC4046 chips. The idea is that you have the Voltage Controlled Oscillator (VCO) running at 60 times the input rate with a divide by 60 device in the feedback path to the phase comparator. The relatively low speeds may make lock-up times too long (the time time it takes to sort itself out) so some experimentation is required.
Regards, Dave
Peter G. Shaw21/10/2009 16:05:42
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1531 forum posts
44 photos
Hi,
Depending on your requirement, and your speed rating, you could use a cycle computer.
 
I have one bought from Halfords which by careful selection of the wheel diameter (1667 I think) means that the kph reading on the display can be taken as rpm. I did find that there were slight restrictions in that as the speed increased, the display at certain points automatically reduced it's resolution, and that above another speed, it stopped working altogether.
 
Nevertheless, from my point of view it allowed be to roughly calibrate my milling machine.
 
Regards,
 
Peter G. Shaw

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