I implemented an optical RPM sensor. It allows very precise measurements even during acceleration. My CD inertia wheel shipped yesterday. We have our dyno enclosed, so it can explode without risks... I am planning to install multiple reflective tapes per turn to obtain high accuracy and precision on the rotation.

While doing this implementation, I improved the precision of the electrical RPM sensor quite a bit. It was accurate before, but noisy. Now, the sensor is super precise, with pretty much no delay. At 20kRPM, the interrupt triggers every 0.0015 seconds, and the sensor measures the time between interrupts with 0.000004s accuracy. I am using the interrupt with timer 0 on the Atmega 328. The signal is very smooth. The following image is the graph of the two sensors. There is no low pass filters.




Anyhow, I think all of this will be important for dynamic tests. You really need a precise and accurate RPM measurement.

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