Make a PC sense the speed of a moving object


Thread Starter


Can any body tell me how I can make a computer sense the speed of a rotating shaft or a moving object without touching it using sensor and other circuits. Please do help me.

James Ingraham

A quick search on "industrial tachometer" on Yahoo produced a number of possibilities. (My favorite people for data aquisition, National Instruments, doesn't appear to have sell tachometer.) Monarch Instrument at
"": had a very nice selection of handheld non-contact tachs that have communication options like RS-232. I've never dealt with this company, so I can't vouch for them.

-James Ingraham
Sage Automation, Inc.

Israel Cabrera

I can help to meassure the speed of a rotating shaft without touching it but in case of a moving object it's difficult to generalizate because of the differences in matterials so I can't help you in this field.

In case of a moving shaft it will rotate at some
RPM's so the best solution is to get/build a digital tachometer with an infrared LED to
meassure the speed. There are lot's of digital tacho's available on the market, you can try to adapt one to the PC. As digital IFR tacho's display's the speed in a digital way, it will not be difficult to hack one, obtain a digital signal from it, and attach it to the LPT Port (printer port).

The programming is your choice... but I should do it in linux with 'C'.

[email protected]

Melvin Caldwell

I detect the speed of conveyor belts by welding a small metal tab on the inside rim of a pulley. A non-contact proximity detector is then placed near the tab and the pulses are detected as the pulley rotates. Using some math we can calculate the circumference of the pulley and with the pulse
information convert that to either RPM or Feet per minute etc.

You will still need to have some sort of input device and program to get your PC to recognize this information. There are several companies that make I/O cards for PC's

For a quick temporary and cheap idea:

I made a simple input device to do this by using a contact in parallel with the mouse button on a PC. I wrote a small program to detect the mouse
button closures. I used this with my laptop when I was in the field making some adjustments and calculations.

Keep in mind that how well this works will depend on the speed of the pulses, speed of the PC and any other activities your PC is performing.
There is a point where the PC and mechanical contacts may not be able to process high speed information.

If you want more information about the mouse modification and / or the program email me and I send it to you

Melvin L. Caldwell Jr.
[email protected]