Meassuring frequency of external signal

[jelinpe7]

Posted on February 14, 2015 at 12:39

Hi, is it possible to meassure frequency of external signal via Input capture, if the external signal is only from 0,5V to 2,5V (not from 0V to Vdd - 3V) and it is sine wave (not square wave)?

Thank you

[raptorhal2]

Posted on February 14, 2015 at 15:22

Check the ''I/O Port Characteristics'' section in the data sheet for your device. For example, the F405 minimum signal voltage is 2 volts.

Sine or square wave shouldn't matter, but the measured frequency for each sample will be more effected by signal noise for the sine wave. Cheers, Hal

[Tesla DeLorean]

Posted on February 14, 2015 at 16:18

There is a schmitt trigger on the input, it should be able to do a reasonable job of thresholding the signal as described.

Depending on the frequency you'd either want to count the number of pulses over a observation interval, or use the input capture to measure the period of a single cycle (or multiple using the input prescaler).