OK, then there are a few ways to record the exact angle at the time some event happens. But always some reference signal from a reference point is needed. If this is a flywheel on a machine, or on a dynamometer testing an engine, then an encoder can be used, which makes it very simple. The problem with getting exact position readings on an engine is that the rotation speed varies a bit during the revolution.
If a few revolutions at a fairly constant RPM are available, then one method would use two counters and a time base frequency, and a ratio counter, either in hardware or in software. As the flywheel rotates and the reference point passes, both counters reset, and then when the event happens the one counter is latched, or else the single counter value is latched while the main counter continues until the reference point count is latched. At that point the proportion of the revolution past the reference is equal to the ratio of the two counts.
The accuracy of this method is limited by the stability of the speed and the resolution of the reference point sensor. With a high enough time base frequency the accuracy can be fractions of a degree.
The stability of the reference frequency does not need to be really high, but it does need to have good short term stability so as not to vary during the revolution.

 

Thank you for that, Yes I was assuming that all that stuff was implied. Sorry if I left that part out. I was planning on having something to record the locations like a chip or Arduino like board somewhere in the system, but not on the moving parts.
I was just posting here for some ideas on how to record the locations. Not really concerned w/rotation speed changing w/in the rotation. The sensor will pick up the correct location on the next pass.
Thank you.

 

Is this an engine application or something else? Or is it a non-running engine, driven externally by some other means, that is being checked. Compressors and pumps sometimes use similar checking methods is why I am asking.

 

Its a flywheel on a piece of farm equipment.

Look at this, here is team that was successful at creating something like this with piezo capacitor, but I don't want all the components. Was trying to be as simple as possible. Link

 

Its a flywheel on a piece of farm equipment.

Look at this, here is team that was successful at creating something like this with piezo capacitor, but I don't want all the components. Was trying to be as simple as possible. Link

As expected the piezo capacitor is a energy transducer converting mechanical energy into electrical energy for a usage with a traditional encoder and transmitter circuit. The energy transducer here and just about in any practical circuit doesn't directly transmit RF.

 

The counters concept is quite simple, and it could be as simple as having signal conditioners for the reference and event inputs and a pair of latches off a binary counter. And the stable time base could be one of those 4-pin crystal clock oscillators. The outputs could be as simple as LEDs driven by the latches. High brightness LEDs can easily be read when fed by 12 volt CMOS logic. If less resolution is needed then an auto-mechanic's duty cycle meter could read the reference and event pulses and provide whatever display that unit utilized. I can' get much simpler without suggesting a timing light triggered by the event and illuminating markings on the flywheel. Then whatever event is being watched needs only to generate some kind of trigger, which could be a magnetic pulse or a grounding contact, about as simple as can be.