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photo interrupter , lichtsluisje HBM BF30 toerenteller

I got a second hand (but barely used) BF30 clone milling machine.
The rpm meter was not working correctly (not showing high RPM, nonsense numbers)
I investigated and found the photo interrupter on the spindle axle.
It was covered in grease (sticky brown Chinese transport grease).
After taking it apart I noticed all holes were over-sized (and slotted).
Mounting the thing back and getting the perfect alignment would be a gamble (I like more precise work, but it appears all holes in this machine are too large or slotted, every edge is sharp and needs deburring).

I made a little tool to check the workings, it is impossible to adjust once the motor is mounted so it has to be correct before I put the motor back on the machine.

Here is the setup :



The ring has 16 holes, so the rpm is more accurately (or quickly) determined.
How this works : the system counts number of pulses in one second and from that displays the number of rpm ( NL: toerental in omwentelingen per minuut)  (rounds per minute) 60 seconds in 1 minute, so 1 pulse per second would be 60 rpm (if we had only one hole), since we have 16 holes, 16 pulses per second would be 60 rpm)
For some reason rotational frequency is expressed in rounds per minute and not in rounds per second, which be more in line with scientific practice.

The disk is blocking the flow of light (interrupting) and the LED turns off.


I used a very simple test to verify alignment.
Not using any transistor, logic gates or op-amps, just an efficient blue LED and 2 resistors.


Close up of total implementation


Test on the workbench, no problems here.


The fact that the output signal is proportional and not clipped into a logic value actually helps with alignment, the led can glow at half power if some light is received, it is very handy to use this "Analogue" alignment tool.





Just a solution for my little setup, use if you like, if it does not work, sorry about that.

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