Video tachometer

When the frame rate of a video matches the speed of a particular part, the effect is the same as using a strobe light. In the video, that part freezes.

Since the frame rate of a video can be adjusted, this effect can be used to determine the rotational speed of a part.

The smartphone must support slow-motion video recording (filming at a high frame rate). This is the case for all smartphones starting with iPhone 5S. The range is as follows:

• 6 - 240 Hz (360 - 14400 RPM), for all phones from iPhone 6 onward
• 6 - 120 Hz (360 - 7200 RPM), for iPhone 5S

To get a clear image, good lighting is important. The clarity of the image is controlled by the exposure of the video (exposure time and light sensitivity (ISO)). If the exposure time is reduced, the image will increase in clarity, but brightness will lower. To increase the brightness, you need to raise the camera's light sensitivity (ISO). You also need to manually adjust the focus of the camera.

The video tachometer measures the rotational speed in exactly the same way a stroboscopic tachometer would.