Tachometer Idea

Look at the name plate for rpm?

Blade says maximum speed 6000 RPM. Also, 6000 RPM for edge shaping blade attachments.

Dust oil and mosquito's .. Any not hermetic covered optoelectronic will fail sooner or later.

This is speed measurement only and not for speed regulation. Adjustable pulley on motor allows change of blade RPM's.

Better ask god how much RPMs you have.

I found a hall effect sensor and a magnet on a bike. the magnet goes on one side of the steel disc, hall sensor on the other. holes in the disc allow the hall sensor to detect the magnet. this makes it a hermetically sealed system suitable for dusty and wet conditions. downside is you need holes in the disc and a frequency divider. might work if you line it up with the saw teeth though, then divide by the number of teeth

another way would be to use an IR transmitter and receiver in one package. point it at a reflective surface (eg. a steel saw) and it sees the beam. point it at a black surface and it can't see the beam. put a black dot on the sawblade and point the thing at it and count that

@faceblast some saw blades already have holes about 1.5 to 3 inches away from the center so @Imccoig could use those, and if he wants the rpm at the teeth all he needs to do is a few more calculations and it would work.

You could try a proximity sensor lined up near the teeth, which would put out a pulse per tooth and the pulses could be fed into a counter circuit with an ADC and 7 segment LED display.

Thanks for all the great ideas!

Handheld Photo Laser Tachometer Tester at $ 12.99 USD looks like it could do the job. High intensity class II laser measures from 2.5 - 99,999 RPM. Very easy to use by applying a reflective mark (included in package) on target object, then aim at the mark by Laser beam.

At this relatively low velocity of around 100 counts per sec. (No need to measure the teeth velocity....just multiply by the constant), I would think that any of these methods would work. If you were dealing with extremely high velocities then a laser with a diffraction grating might be a better idea (I used that method to measure the groove width on a CD and to measure the speed of light). The difficulty for me would be getting an accurate/precise readout on a rigged up calculator .....it would need to respond faster than the E.C. displays....Perhaps one of the guys here can put forth a handy circuit to measure fast rpm which can be displayed on a readout with a reasonably low error margin.

See also variable reluctance magnetic pickup half way down this pdf data sheet for the above frequency/velocity type of measurements. https://www.google.co.uk/url?sa=t&source=web&rct=j&url=http://www.ti.com/cn/lit/gpn/lm2917-n&ved=0ahUKEwien-r10J_LAhVJnRoKHcLLA-EQFggbMAA&usg=AFQjCNFeyiumLQrGhpt-XWsf2NtYsmxC1g

@2ctiby, quite a versatile component. Blade speed would be 2000 to 6000 rpm range. Above component doubles output so that would be 12000 rpm square wave to measure. Reluctance wheel at 6000 rpm would have to be devised also. Thanks for sharing component information!

I'm just wondering if we are missing something simpler here. A car engine with throttle is not all that different than 6000 rpm. I used to hold an oscilloscope near to mine many years ago and it would pick up the electical impulses. I could nicely see the plugs firing and tell if one was not working. I could also view the capacitor discharging just like here on EC. and it was a great way to discover if the capacitor or points were malfunctioning. Using the oscilloscope that way made it easy to calculate the rpm .....never had a tachometer on the dashboard. I then went on to detect the electicity with a tiny simple FM transmitter and so pick up the signal back in doors instead of carrying the big heafty valve oscilloscope to the vehicle. The next step was when I wrote a program in BASIC and used it on the sinclair spectrum....That pinpointed the peak pixel of the oscilloscope waves along with the distance between each. A printout was then presented of the points dwell angle, rpm, and an indication of any mis-firing etc......good old days...hope I haven't bored you. A little FM transmitter and an oscilloscope and you might be in biz ??

I tried air tube close to blade teeth with headphone mike inside tube to AR Oscilloscope app on phone. Waves did not look consistent enough for accurate reading. It seems something simple should work. I thought about compressed air through hole in saw blade for pulsing sound but saw generates other noise. My brother thought he might have some tool to measure rpm. I am waiting also to hear from him.

Tried any lasers?