Hi everyone!
I need some valued advice please!

I am planning to use an optical switch to measure the speed of a motor which will be turning from speeds of between 20Hz to 100Hz, 1200-6000Rpm.
I am unsure which switch to use, to be honest i'm bamboozled with information,
Am i correct in thinking that the faster the rise and fall time the quicker the measurement?
shall i use the schmitt trigger, totem pole, phototransistor or transistor?
Thanks!

 

At 100Hz, the period is 10ms. Even if it took 1ms for the photo-detector to turn on or turn off, it would be fast enough.
What do you have available locally?

 

thanks Mike!
so are you advising not to worry about the rise and fall?
Also would it be adviseable to use the schmitt trigger version instead of a phototransistor with a pull up resistor?
Cheers!

 

thanks Mike!
so are you advising not to worry about the rise and fall?
Also would it be adviseable to use the schmitt trigger version instead of a phototransistor with a pull up resistor?
Cheers!

Are you talking about a photo-interrupter like this?

 

Yeah, that is a schmitt trigger example am i correct?
the types i have been looking at are Number1 and like this Number 2,
thanks for your advice!!

 

For your non-critical application, either one will work. The schmitt trigger version has a no-bounce output pulse, which might be an advantage if you are using a counter or uprocessor.

 

I will be measuring measuring the vibration of an unbalanced motor using a pc oscilloscope to determine the frequency! I will order the scmitt trigger version and have a play! thanks again for your advice!
Kind regards

 

Are you trying to get a time-varying analog signal, or just a digital pulse every time a slot passes the beam? If you want analog, then get the phototransistor version.

 

thanks, either or should suffice, as long as i can accurately determine the speed of the motor, i might just get one of each and have a look, i have wired a simple IR transmitter and receiver which works but is not that accurate due to it not being shielded from day light i think! hopefully one of these will be able to measure the speed!