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I measured the frequency of motors with an accelerometer (ADXL335), but the frequency from my measurement is a lot different from the frequency specified in the product page.

I tested with two motors.

1) http://www.adafruit.com/product/1201 I got 220-250 Hz with 5V, but the product page shows that the frequency should be around 180Hz

2) https://catalog.precisionmicrodrives.com/order-parts/product/303-100-3mm-vibration-motor-8mm-type I got 170~180Hz with 3.6V, but the datasheet shows that it should be around 280Hz.

The vibration frequency in the datasheet has tolerance, and the frequency may vary with different mounted materials. I thought that my measurement is showing different frequencies because my measurement setup (mounted material, variation in the motor) would be different from what manufacturers used.

Therefore, I want to make sure that my measurement is correct by generating the exact frequency and measuring it again with the accelerometer.

Can you suggest any way to generate exact frequency? The frequency should not be higher than around 1 kHz because the accelerometer has limited sampling rate.

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You could use a speaker and a sound card. Should be very accurate.

You should be able to find an old copy of CoolEdit and generate a minute or two long pure sine .wav file if you don't have any sound editing software already.

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  • \$\begingroup\$ Thank you for comment! Can I make 100~200Hz vibration with a speaker? Can I use a piezo buzzer? (adafruit.com/products/160) \$\endgroup\$ – user2270860 Aug 29 '15 at 19:11
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    \$\begingroup\$ Speaker (computer speaker) would be better at 100-200Hz. Piezo at kHz. \$\endgroup\$ – Spehro Pefhany Aug 29 '15 at 19:15
  • \$\begingroup\$ Can I measure the frequency of speaker sound with accelerometer? I want to make an exact frequency to confirm that my measurement setup is correct. \$\endgroup\$ – user2270860 Aug 30 '15 at 16:03
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EDIT - My apologies - my previous answer was completely wrong, and I can only plead brain fart.

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  • \$\begingroup\$ 16000 rpm is 266 Hz. What did you see? The frequency red line in the graph, isn't it? \$\endgroup\$ – user2270860 Aug 29 '15 at 20:00

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