# PC-based audio tachometer!



## junebug1701

I was wondering if such a thing existed, so after some Googling, I found that it does. A clever programmer has designed a program called Audio Tach that uses a cheap microphone and your computer's sound card to display the RPM's of just about any type of motor that makes a repetitive sound. Although designed for R/C helicopters, it seems like it would work fine for small gas engines. And best of all it's free! If you have a laptop, you can load up this small program and take it to the shop to "listen" for the speed of the engine while tuning or setting the governor. Some laptops already have a built-in mic, but my Toshiba doesn't so I'm using a cheap Labtec stick microphone. The programmer has set it up to listen to the sound of the copter blades, so it has options for 2 blades, 3 blades and so forth. I think that with a 4-stroke engine the 2 blade option should work. On a 2-stroke you would need to multiply the reading by 2. I'm going to try playing with this thing for the next couple of days and see how it works. Here's a screen shot of the program:










Read about the program here:

http://helifreak.com/showthread.php?t=151698

And download it here:

Original version: Audio Tach

Second version (goes up to 30,000 RPM):Audio Tach 30000


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## junebug1701

I played with this today for a little while and it seems to work OK. Took my laptop out to the shop and fired up the old Whipper Clipper and it seems to run at about 3750 RPM. If I move the throttle so that it's partially choked the speed goes up to a little over 4000. This is with no load. Background noise can be a problem--it was picking up the sound of the A/C window unit until the edger motor drowned it out. Tried it out back with an old Yard-Man mower with a Briggs Quantum and it was surging a bit so it was hard for the program to lock on. After it smoothed out it showed about 3200 RPM, so I need to adjust that one. I'll try a different microphone next time and see how it compares.


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