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.