A smartphone strobe tachometer / timing light.
Suppose you have a rotating or oscillating piece of equipment (eg. a spinning shaft, vibrating rod), and you want to know how fast it is moving, this app can help you. If the strobe light that flashes at the same speed as the vibration or rotation, the item will appear to ‘freeze’ under the strobe light. You know the frequency of the flashing light, so you can tell the frequency of the vibration or the speed of the shaft.
Dim the ambient lights until the strobe is the dominant light source. Shine the light at the item spinning / vibrating and adjust the frequency until the item appears to be still. The frequency of the light is the same as that of the object and you can read off the frequency (HZ) or speed (RPM). Start high and work your way down.
If your light frequency is 1/2 or 1/3 or 1/4 x or any exact proportion of the shaft speed, the shaft will also appear stationary. This is called a harmonic. To ensure you don’t have a harmonic, double the frequency and check again. The highest frequency with effectively 'stops' the motion of the shaft is the true frequency.
Flashing lights occasionally cause epilepsy or other troubles in some people. If you feel unwell using this app then stop. This app is a tool, not a toy, please be careful.
Here is a good video about how to use this tool: http://www.youtube.com/watch?v=MqLwgisyjjw
Ratings and Reviews
Nice Idea, but poor implimentation.
I was trying to measure the speed of my ceiling fan with this strope. Interface is simple, but I think it is a little too simple. Scroll wheel to adjust speed (nice), but strobe does not change until scroll wheel is stopped. The 2x and 1/2x buttons (pro version) changes the speed indicator, but the strope does not change speed making it useless. No option for changing the duty cycle of the strobe. No button options for adjusting the speed either. I suggest waiting util the next version, as this version is in need of some bug fixes and some enhancments.
A known device of max 2500rpm is getting readings of 4000rpm at half speed. While it does make the rotation stop to take a reading it is completely inaccurate giving unusable readings. Likely the software has not been tested against working devices. I certainly wouldn't pay for a pro Version when the free version doesn't work.
Does what it says
The app works great. The flash LED on my iPhone 5S isn't fast enough to effectively operate over about 80hz though. The rise and fall time of the LED is too long, so the strobing becomes too subtle to be effective at higher frequencies. But thats not a flaw of the app or the LED, just a consequence of using the flash for something other than its intended purpose. This app works very well at frequencies that are perceivable to the naked eye.
With Family Sharing set up, up to six family members can use this app.