get the RPM of my DIY DYNO into Labview. What i already did and have:
Inductive Sensor with perforatet Disk
Recitified 0 - 15V AC to 1-4V DC with a bridge rectifier
--> Works, measurable with multimeter up to 1500 RPM (Stable voltage which follows the RPM)
Problem:
I only get a really noisy signal when i read the analog value (It works fine when i put a 1.5 Volt battery on --> constant value) but the RPM signal is so noisy and goes up to 5 Volt (My multimeter says only 3 Volts -.-???).
i testet a program with "analog read" and "continues sample".. (picture)
When i rectify a voltage of 15 V ac from a transformer the measurement is no problem with arduino/labview (picture)...
What i thought about:
As an Example 600 RPM
My perforatet Disk has 29 teth.. so 600 RPM = 10 1/s --> 10*29 teth = 290 signals per second --> Can i measure this with such a precission?
Do you have some solution or input? i don't really know what to do....
If you use a bridge rectifier on an AC signal, you need to be aware that the apparent frequency of the pulses in the signal appears to double, as the negative peaks get "flipped over" to become additional positive peaks. If that doesn't make sense, the diagram with any elementary explanation of what a bridge rectifier does, should make it clearer.
If you are getting 290 pulses per second, and you want to sample them often enough to detect the shape and timing of the pulses, then you probably need something close to 2000 samples per second. This is possible, but getting close to the limit of what the arduino will do, if it is doing anything else.
If I was doing this, I would use a comparator circuit, choose some reference voltage say 2.5 V, and generate a pulse each time the signal goes above 2.5V, and trigger an interrupt on the arduino with that. You still might have a problem with noise causing some extra transitions. But if you are only expecting a pulse after 3 to 4 milliseconds, you can ignore extraneous pulses which occur very soon after the previous one.
